9'<GσI┐M│Q╚TmW√_æf kΣm«s∞v┘Ç▄ê╢îÅ0ôÿc₧éí2Ñ »┼╡ à╝y┴ m╞ ,═╕╫ DΓ mµ ┘Θδδ ²φ┤≥YDivisions of the Brain
The surface of the cerebral hemispheres is folded into deep fissures (sulci) and bumps (gyri) which triple the total surface area. The most prominent sulci are used to divide each cerebral hemisphere into four main lobes. For example, the central sulci separate the frontal lobes from the parietal lobes. In the 3-D model above, the frontal lobes are shown in light blue, the parietal lobes in pink, the temporal lobes in dark blue, and the occipital lobes in green. These lobes have the same names as the skull bones that overlie them. Besides the all important cerebral hemispheres, the other large structures of the brain visible in the 3-D model above are the cerebellum, shown in yellow, and the brainstem, which is shown in orange. The brain stem is the most primitive part of the brain. It is responsible for sustaining the basic functions of life such as breathing and blood pressure regulation. The brainstem directs these functions without any conscious intervention.
The last structure visible in the 3-D model above is the pituitary. It is seen as a small reddish ball protruding from the bottom of the frontal lobes. The pituitary is the master gland in the body. It has significant influence over many of the body's processes. The pituitary controls these functions by releasing hormones. Hormones are chemicals that are released into the blood and carried to distant parts of the body where they exert their effects. Two of the many pituitary hormones are thyroid stimulating hormone (TSH), which controls the thyroid gland, and growth hormone (GH), which stimulates cell division and growth.
YDivisions of the Brain
The surface of the cerebral hemispheres is folded into deep fissures (sulci) and bumps (gyri) which triple the total surface area. The most prominent sulci are used to divide each cerebral hemisphere into four main lobes. For example, the central sulci separate the frontal lobes from the parietal lobes. In the 3-D model above, the frontal lobes are shown in light blue, the parietal lobes in pink, the temporal lobes in dark blue, and the occipital lobes in green. These lobes have the same names as the skull bones that overlie them. Besides the all important cerebral hemispheres, the other large structures of the brain visible in the 3-D model above are the cerebellum, shown in yellow, and the brainstem, which is shown in orange. The brain stem is the most primitive part of the brain. It is responsible for sustaining the basic functions of life such as breathing and blood pressure regulation. The brainstem directs these functions without any conscious intervention.
The last structure visible in the 3-D model above is the pituitary. It is seen as a small reddish ball protruding from the bottom of the frontal lobes. The pituitary is the master gland in the body. It has significant influence over many of the body's processes. The pituitary controls these functions by releasing hormones. Hormones are chemicals that are released into the blood and carried to distant parts of the body where they exert their effects. Two of the many pituitary hormones are thyroid stimulating hormone (TSH), which controls the thyroid gland, and growth hormone (GH), which stimulates cell division and growth.
&The Ear
The ear is the organ of hearing and balance. The ear is commonly divided into the outer ear, the middle ear, and the inner ear. The largest part of the outer ear is the pinna which is designed to channel sound waves into the ear canal. At the end of the ear canal is the eardrum (tympanic membrane). The eardrum is part of the middle ear, along with three tiny bones (ossicles) that form a chain. These bones are the malleus (hammer), incus (anvil), and stapes (stirrup). The airspace within the middle air is blocked from the outside by the eardrum, but it does connect to the throat via the eustachian tube. The inner ear consists of the cochlea, the semicircular canals, and the eighth cranial nerve. The base of the stapes fills the oval window which serves as the entrance to the inner ear.
&The Ear
The ear is the organ of hearing and balance. The ear is commonly divided into the outer ear, the middle ear, and the inner ear. The largest part of the outer ear is the pinna which is designed to channel sound waves into the ear canal. At the end of the ear canal is the eardrum (tympanic membrane). The eardrum is part of the middle ear, along with three tiny bones (ossicles) that form a chain. These bones are the malleus (hammer), incus (anvil), and stapes (stirrup). The airspace within the middle air is blocked from the outside by the eardrum, but it does connect to the throat via the eustachian tube. The inner ear consists of the cochlea, the semicircular canals, and the eighth cranial nerve. The base of the stapes fills the oval window which serves as the entrance to the inner ear.
tThe Eye
The eye is a complex organ that provides the sense of sight. The eyeball has a tough outer coat called the "sclera" which forms the white part of the eye. The circular, most forward part of the eye is called the "cornea." The cornea is transparent. Behind the cornea is a fluid filled space called the aqueous humor (watery fluid). Moving further back, there is the colored part of the eye called the iris with a black hole in its center called the pupil. The iris changes the size of the pupil in response to changes in brightness. Directly behind the iris is the lens. The lens changes shape to help focus the light rays entering the eye, but surprisingly, most of the focussing of light rays is done by the cornea. The main body of the eye, behind the lens, is filled with a clear gel called the vitreous humor. At the very back of the eye is the retina. The light rays fall on the retina which converts those light rays into signals that are processed by the brain, allowing us to see. The eyeball itself is moved by six delicate muscles called the ocular muscles. Four of these muscles are shown in the 3-D model above.
tThe Eye
The eye is a complex organ that provides the sense of sight. The eyeball has a tough outer coat called the "sclera" which forms the white part of the eye. The circular, most forward part of the eye is called the "cornea." The cornea is transparent. Behind the cornea is a fluid filled space called the aqueous humor (watery fluid). Moving further back, there is the colored part of the eye called the iris with a black hole in its center called the pupil. The iris changes the size of the pupil in response to changes in brightness. Directly behind the iris is the lens. The lens changes shape to help focus the light rays entering the eye, but surprisingly, most of the focussing of light rays is done by the cornea. The main body of the eye, behind the lens, is filled with a clear gel called the vitreous humor. At the very back of the eye is the retina. The light rays fall on the retina which converts those light rays into signals that are processed by the brain, allowing us to see. The eyeball itself is moved by six delicate muscles called the ocular muscles. Four of these muscles are shown in the 3-D model above.
ÄThe Gallbladder
The gallbladder is a small sac which sits just beneath the liver. Its only role is to concentrate bile and then release it when food is passing through the small intestine. Bile is a sticky, green fluid produced by the liver. Bile serves both as a fluid which helps the body to absorb fats, and as a way to eliminate toxins. All the liver cells make bile at a constant rate. The bile is released into a network of bile ducts that all come together to form the common hepatic duct. The gallbladder is connected to the common hepatic duct by the cystic duct. Most of the time, bile flows up the cystic duct and into the gallbladder for storage. When food passes from the stomach into the duodenum, however, a hormone (cholecystokinin) is released which signals the gallbladder to contract. The bile is squeezed back up through the cystic duct, and down the common bile duct into the small intestine.
CThe Digital Hand
The hand is the most versatile part of the skeleton. It enables people to grasp and manipulate objects. The hand is comprised of the wrist (carpals), palm (metacarpals), and fingers (phalanges). There are three main nerves which travel to the hand; the median nerve, the ulnar nerve, and the radial nerve. Each of these three nerves connects with a specific part of the hand to permit movement and sensation. Intricate hand movements are achieved by using the small muscles that are contained entirely within the hand (the intrinsic muscles), and the much larger forearm muscles. The forearm muscles are connected to the bones of the hand by long tendons. Tendons and ligaments are often confused with one another. A tendon is the fibrous attachment of a muscle to a bone. A ligament is a fibrous attachment between bones.
CThe Digital Hand
The hand is the most versatile part of the skeleton. It enables people to grasp and manipulate objects. The hand is comprised of the wrist (carpals), palm (metacarpals), and fingers (phalanges). There are three main nerves which travel to the hand: the median nerve, the ulnar nerve, and the radial nerve. Each of these three nerves connects with a specific part of the hand to permit movement and sensation. Intricate hand movements are achieved by using the small muscles that are contained entirely within the hand (the intrinsic muscles), and the much larger forearm muscles. The forearm muscles are connected to the bones of the hand by long tendons. Tendons and ligaments are often confused with one another. A tendon is the fibrous attachment of a muscle to a bone. A ligament is a fibrous attachment between bones.
;
The Heart
The heart is a powerful pump that beats continuously during life to circulate the blood throughout the body. The heart has four separate chambers. There are two atria to receive the blood returning to the heart, and two ventricles to pump the blood back out. Each of these four chambers has a one-way valve to ensure that blood flow is always in the forward direction. The heart is actually better described as two pumps that act in series. With each beat, the right ventricle pumps deoxygenated blood to the lungs, and the left ventricle pumps oxygenated blood to the body. The two sides of the heart are not identical, however. The left ventricle is much thicker and stronger than the right ventricle. Why is this so? It is easy to see that the right and left sides of the heart must always pump the same volume of blood. If they didn't, serious bottlenecks would develop in the circulation. However, the resistance to blood flow is much greater in the body than it is in the lungs. The left ventricle thus has to work harder and contract more forcefully to keep up with the right ventricle. This explains why the left ventricle has much thicker muscular walls than the right ventricle.
Let us follow the course of a single red blood cell in more detail as it moves through the heart. At the outset of the journey, the blood cell returns from the body via the vena cava and enters the right atrium. The right atrium contracts and pumps the blood cell across the tricuspid valve and into the right ventricle. Soon after that, the right ventricle contracts and pumps the blood cell across the pulmonic valve and into the pulmonary artery. The blood cell can then go either right or left to enter one of the lungs. While in the lungs, the blood cell unloads carbon dioxide and picks up oxygen. Next the blood cell returns to the left atrium via one of the pulmonary veins. The blood cell then crosses the mitral valve to enter the left ventricle. At this point, the left ventricle contracts forcefully to send the blood cell across the aortic valve and out into the body. After unloading its oxygen somewhere in the body, the blood cell enters a vein and returns via the vena cava to the right atrium where it can begin the cycle once again. On average, this whole journey takes about two minutes.
Red blood cells only last about 4 months before they wear out, but the heart never rests. During an average lifetime, the heart beats approximately 2.5 billion times. The heart is a very well designed pump indeed. It is more reliable and energy efficient than any pump ever created by man.
;
The Heart
The heart is a powerful pump that beats continuously during life to circulate the blood throughout the body. The heart has four separate chambers. There are two atria to receive the blood returning to the heart, and two ventricles to pump the blood back out. Each of these four chambers has a one-way valve to ensure that blood flow is always in the forward direction. The heart is actually better described as two pumps that act in series. With each beat, the right ventricle pumps deoxygenated blood to the lungs, and the left ventricle pumps oxygenated blood to the body. The two sides of the heart are not identical, however. The left ventricle is much thicker and stronger than the right ventricle. Why is this so? It is easy to see that the right and left sides of the heart must always pump the same volume of blood. If they didn't, serious bottlenecks would develop in the circulation. However, the resistance to blood flow is much greater in the body than it is in the lungs. The left ventricle thus has to work harder and contract more forcefully to keep up with the right ventricle. This explains why the left ventricle has much thicker muscular walls than the right ventricle.
Let us follow the course of a single red blood cell in more detail as it moves through the heart. At the outset of the journey, the blood cell returns from the body via the vena cava and enters the right atrium. The right atrium contracts and pumps the blood cell across the tricuspid valve and into the right ventricle. Soon after that, the right ventricle contracts and pumps the blood cell across the pulmonic valve and into the pulmonary artery. The blood cell can then go either right or left to enter one of the lungs. While in the lungs, the blood cell unloads carbon dioxide and picks up oxygen. Next the blood cell returns to the left atrium via one of the pulmonary veins. The blood cell then crosses the mitral valve to enter the left ventricle. At this point, the left ventricle contracts forcefully to send the blood cell across the aortic valve and out into the body. After unloading its oxygen somewhere in the body, the blood cell enters a vein and returns via the vena cava to the right atrium where it can begin the cycle once again. On average, this whole journey takes about two minutes.
Red blood cells only last about 4 months before they wear out, but the heart never rests. During an average lifetime, the heart beats approximately 2.5 billion times. The heart is a very well designed pump indeed. It is more reliable and energy efficient than any pump ever created by man.
│Index
Welcome to the Body Adventure index. Just click on a letter to access a subject of interest. It is also possible to go directly to a subject by typing the word at any time.
The Intestine
The intestine is the major part of the digestive system, extending from the duodenum to the anus. It is generally divided into the small intestine and the large intestine. The primary function of the small intestine is to complete the digestion of food and then absorb the useful nutrients into the blood. The small intestine consists of three major sections called the "duodenum," the "jejunum," and the "ileum." At the end of the ileum, unabsorbed material containing a large volume of water is passed on to the large intestine. The function of the large intestine is to resorb all the excess water from the undigested food. This process forms feces which are then eliminated. The appendix is a tiny, finger-like process extending from the bottom of the cecum, on the right side of the large intestine. The appendix has no known function. Occasionally, the appendix becomes infected, a condition called appendicitis. Appendicitis is generally treated by simply removing the appendix. This is the most common abdominal operation.
The Intestine
The intestine is the major part of the digestive system, extending from the duodenum to the anus. It is generally divided into the small intestine and the large intestine. The primary function of the small intestine is to complete the digestion of food and then absorb the useful nutrients into the blood. The small intestine consists of three major sections called the "duodenum," the "jejunum," and the "ileum." At the end of the ileum, unabsorbed material containing a large volume of water is passed on to the large intestine. The function of the large intestine is to resorb all the excess water from the undigested food. This process forms feces which are then eliminated. The appendix is a tiny, finger-like process extending from the bottom of the cecum, on the right side of the large intestine. The appendix has no known function. Occasionally, the appendix becomes infected, a condition called appendicitis. Appendicitis is generally treated by simply removing the appendix. This is the most common abdominal operation.
⌠The Kidneys
There are two kidneys, each about six inches in length. The main functions of the kidneys are to regulate the amount of water and salt within the body, to maintain the proper acid-base balance in the body, and to eliminate waste products from the blood. The kidneys are also responsible for making a few key hormones. One of these hormones (erythropoietin) is responsible for stimulating production of red blood cells, while another (renin) plays an important role in regulating blood pressure.
-The Foot and Ankle
The ankle is a hinge joint connecting the bones of the lower leg (tibia and fibula) and the uppermost bone of the foot (talus). The ankle is held together by several strong ligaments which provide stability and prevent excessive movement. The ankle only allows simple upward and downward motions of the foot. Other foot movements require motion of the joints within the foot itself. Because the ankle is subject to great stress, sprains of the ankle ligaments are very common. Each foot has 26 separate bones. The two largest foot bones are the calcaneus (heel bone), and the talus. Long tendons attach many of the bones of the foot to strong muscles located in the lower leg.
There are a number of disorders that are frequently seen in the foot. These include corns, bunions, and gout. Corns are small areas of thickened skin usually caused by tight fitting shoes. A bunion is a firm, fluid filled lesion that forms over the base of the big toe. Like corns, bunions are usually the result of wearing tight, pointed shoes. Bunions sometimes require surgical removal, and reconstruction of the great toe to prevent them from recurring. Gout is a form of arthritis that commonly affects the joint of the great toe. Gout results from the formation of uric acid crystals within a joint. These crystals cause significant inflammation and pain in the affected joint. A person suffering from an attack of gout in the great toe is generally unable to even stand on the foot. Unlike corns and bunions which are more common in women, gout is 10 times more common in men.
-The Foot and Ankle
The ankle is a hinge joint connecting the bones of the lower leg (tibia and fibula) and the uppermost bone of the foot (talus). The ankle is held together by several strong ligaments which provide stability and prevent excessive movement. The ankle only allows simple upward and downward motions of the foot. Other foot movements require motion of the joints within the foot itself. Because the ankle is subject to great stress, sprains of the ankle ligaments are very common. Each foot has 26 separate bones. The two largest foot bones are the calcaneus (heel bone), and the talus. Long tendons attach many of the bones of the foot to strong muscles located in the lower leg.
There are a number of disorders that are frequently seen in the foot. These include corns, bunions, and gout. Corns are small areas of thickened skin usually caused by tight fitting shoes. A bunion is a firm, fluid filled lesion that forms over the base of the big toe. Like corns, bunions are usually the result of wearing tight, pointed shoes. Bunions sometimes require surgical removal, and reconstruction of the great toe to prevent them from recurring. Gout is a form of arthritis that commonly affects the joint of the great toe. Gout results from the formation of uric acid crystals within a joint. These crystals cause significant inflammation and pain in the affected joint. A person suffering from an attack of gout in the great toe is generally unable to even stand on the foot. Unlike corns and bunions which are more common in women, gout is 10 times more common in men.
Y The Larynx
The larynx is the organ commonly referred to as the voice box. The 3-D model above shows two of the major components of the larynx: the cricoid cartilage and the arytenoid cartilages. Each of the two vocal cords is tightly stretched between one of the arytenoid cartilages and the cricoid cartilage. Together, the vocal cords form a V structure which vibrates when air is passed over it. Speech is accomplished by moving the vocal cords while they vibrate in order to modulate the sounds that are made. The other major function of the larynx is to prevent choking. Whenever, a person eats or drinks, a structure called the epiglottis covers over the entrance to the larynx to prevent swallowed food from entering the lungs.
Another important structure in the neck is the thyroid gland which lies just in front of the larynx. The thyroid gland uses iodine to make thyroid hormone. This hormone is released into the bloodstream where it plays a very important role in regulating overall body metabolism. People with underactive thyroid glands feel quite tired and sluggish. In contrast, people with overactive thyroid glands experience rapid heart rate, sweating, anxiety, weight loss, and heat intolerance. The most common cause for an overactive thyroid gland is Grave's disease. Graves's disease is an example of an autoimmune disease in which inappropriate antibodies are made which bind to the thyroid gland and stimulate it to produce too much thyroid hormone. This problem is usually treated by administering radioactive iodine which kills off the excess thyroid activity when it is taken up by the thyroid. Studies have shown that this treatment is not only effective, but entirely safe, with no increased incidence of cancer. Another cause of excess thyroid activity is Plumber's disease, a disease in which one, or a few specific thyroid nodules overproduce thyroid hormone. This can also be treated with radioactive iodine, but it is usually more effective to remove the overfunctioning nodules surgically.
When doing thyroid surgery, it is very important not to damage the four tiny parathyroid glands which lie above and below the thyroid on both sides. These glands play a major role in the regulation of body calcium. This an important job because nerve and muscle cells only function correctly when the blood calcium level lies within a very narrow range.
Y The Larynx
The larynx is the organ commonly referred to as the voice box. The 3-D model above shows two of the major components of the larynx: the cricoid cartilage and the arytenoid cartilages. Each of the two vocal cords is tightly stretched between one of the arytenoid cartilages and the cricoid cartilage. Together, the vocal cords form a V structure which vibrates when air is passed over it. Speech is accomplished by moving the vocal cords while they vibrate in order to modulate the sounds that are made. The other major function of the larynx is to prevent choking. Whenever, a person eats or drinks, a structure called the epiglottis covers over the entrance to the larynx to prevent swallowed food from entering the lungs.
Another important structure in the neck is the thyroid gland which lies just in front of the larynx. The thyroid gland uses iodine to make thyroid hormone. This hormone is released into the bloodstream where it plays a very important role in regulating overall body metabolism. People with underactive thyroid glands feel quite tired and sluggish. In contrast, people with overactive thyroid glands experience rapid heart rate, sweating, anxiety, weight loss, and heat intolerance. The most common cause for an overactive thyroid gland is Grave's disease. Graves's disease is an example of an autoimmune disease in which inappropriate antibodies are made which bind to the thyroid gland and stimulate it to produce too much thyroid hormone. This problem is usually treated by administering radioactive iodine which kills off the excess thyroid activity when it is taken up by the thyroid. Studies have shown that this treatment is not only effective, but entirely safe, with no increased incidence of cancer. Another cause of excess thyroid activity is Plumber's disease, a disease in which one, or a few specific thyroid nodules overproduce thyroid hormone. This can also be treated with radioactive iodine, but it is usually more effective to remove the overfunctioning nodules surgically.
When doing thyroid surgery, it is very important not to damage the four tiny parathyroid glands which lie above and below the thyroid on both sides. These glands play a major role in the regulation of body calcium. This an important job because nerve and muscle cells only function correctly when the blood calcium level lies within a very narrow range.
BThe Elbow
The elbow is the hinge joint which connects the lower end of the humerus with the upper ends of the radius and ulna. The elbow permits the arm to be bent by the powerful biceps muscle and then straightened by the triceps muscle. The biceps and triceps thus form a pair of muscles which have opposite actions. It is a general rule that the muscles of the body are organized into pairs or groups which have opposite actions.
The elbow also allows the forearm to be rotated without moving the upper arm. This is very important for some actions such as turning a door knob. This rotation motion is called either supination or pronation. Supination is the action of turning the palm face up when the arm is held straight out, away from the body. Pronation is the action of turning the palm face down when the arm is held straight out. Following the general rule, these important movements are accomplished by a pair of muscles with opposite actions. The words supination and pronation are related to the words supine, which means to lie face up, and prone, which mean to lie down face down.
Repetitive motions can strain the tendons of the elbow and cause pain. Tennis elbow and golfers' elbow are common conditions resulting from overuse and strain of the elbow tendons. Most everyone has felt the pins and needles sensation caused by hitting the tip of their elbow. This is often referred to as hitting the "funny bone." The temporary pain is caused by impingement of the ulnar nerve which travels through a narrow groove, close to the surface of the skin, as it passes over the elbow.
BThe Elbow
The elbow is the hinge joint which connects the lower end of the humerus with the upper ends of the radius and ulna. The elbow permits the arm to be bent by the powerful biceps muscle and then straightened by the triceps muscle. The biceps and triceps thus form a pair of muscles which have opposite actions. It is a general rule that the muscles of the body are organized into pairs or groups which have opposite actions.
The elbow also allows the forearm to be rotated without moving the upper arm. This is very important for some actions such as turning a door knob. This rotation motion is called either supination or pronation. Supination is the action of turning the palm face up when the arm is held straight out, away from the body. Pronation is the action of turning the palm face down when the arm is held straight out. Following the general rule, these important movements are accomplished by a pair of muscles with opposite actions. The words supination and pronation are related to the words supine, which means to lie face up, and prone, which mean to lie down face down.
Repetitive motions can strain the tendons of the elbow and cause pain. Tennis elbow and golfers' elbow are common conditions resulting from overuse and strain of the elbow tendons. Most everyone has felt the pins and needles sensation caused by hitting the tip of their elbow. This is often referred to as hitting the "funny bone." The temporary pain is caused by impingement of the ulnar nerve which travels through a narrow groove, close to the surface of the skin, as it passes over the elbow.
╟The Liver
The liver is the largest and one of the most vital organs. It consists of two main lobes, the right and the left, and a smaller third lobe called the "caudate." The liver is one of two organs, along with the lungs, to receive a dual blood supply. It receives most of its blood (85%) via the portal vein which drains nearly all the blood from the intestine. This ensures that all the absorbed food goes directly to the liver where it can be packaged and stored for use when needed. The liver receives the other 15% of its blood from the hepatic arteries. This second blood supply is also important because the arterial blood is well oxygenated, unlike the venous blood arriving through the portal vein.
┤The Leg
The knee is the hinge joint that connects the main bones of the leg (the femur and the tibia). The kneecap (patella) lies over the front of the joint. There are strong ligaments on both sides of the joint, called the medial and lateral collateral ligaments. There are also two ligaments within the joint, called the anterior and posterior cruciate ligaments. All four of these ligaments serve to connect the bones of the knee, and to provide additional stability. Like other moveable joints, the bony ends of the femur and tibia are separated by protective cartilage which serves as a cushion between the bones. There are two of these cartilage cushions in the knee. They are called the medial and lateral menisci.
The powerful quadriceps muscles are responsible for straightening (extending) the leg at the knee joint. These muscles are in the front of the thigh. The kneecap is actually a large bone within the quadriceps tendon. The quadriceps tendon is thus commonly referred to as the patellar tendon. The hamstrings are the muscles which bend (flex) the knee at the knee joint. These muscles are located in the back of the thigh.
There are a number of common knee injuries. Severe twisting of the knee will frequently sprain one of the knee ligaments. The difference between a sprain and a strain is often confused. A sprain occurs when a ligament (fibrous connection between bones) is damaged. A strain occurs when a muscle or tendon is damaged. Running can sometimes injure the knee by straining the patellar tendon. The cartilage cushions (menisci) within the knee are also frequently damaged by severe twisting. A torn meniscus is very painful, and usually requires surgical repair.
ΣThe Shoulder
The shoulder is a ball and socket joint which connects the arm with the body. Three bones come together to form the shoulder joint. These bones are the humerus (arm), the clavicle (collar bone), and the scapula (shoulder blade). The deltoid muscle sits on top of the upper arm and shoulder. This powerful muscle works to lift the arm away from the body. There is a fluid filled cavity under the deltoid muscle which serves to reduce friction between the muscle and the underlying joint. Occasionally, this cavity becomes inflamed and painful because of excessive motion. This condition is called bursitis. Bursitis can also occur at a number of other joints including the elbow and knee.
The tendons of four muscles merge together around the shoulder joint to form a reinforcing structure called the rotator cuff. The rotator cuff can be damaged by excessive stress. This is why rotator cuff injuries are common among professional athletes, especially baseball pitchers and football quarterbacks. Another common problem is dislocation of the shoulder. In this case, the top of arm (humeral head) comes out of its normal socket (glenoid cavity). Some people have relatively lax shoulder muscles, and are prone to shoulder dislocations.
ΣThe Shoulder
The shoulder is a ball and socket joint which connects the arm with the body. Three bones come together to form the shoulder joint. These bones are the humerus (arm), the clavicle (collar bone), and the scapula (shoulder blade). The deltoid muscle sits on top of the upper arm and shoulder. This powerful muscle works to lift the arm away from the body. There is a fluid filled cavity under the deltoid muscle which serves to reduce friction between the muscle and the underlying joint. Occasionally, this cavity becomes inflamed and painful because of excessive motion. This condition is called bursitis. Bursitis can also occur at a number of other joints including the elbow and knee.
The tendons of four muscles merge together around the shoulder joint to form a reinforcing structure called the rotator cuff. The rotator cuff can be damaged by excessive stress. This is why rotator cuff injuries are common among professional athletes, especially baseball pitchers and football quarterbacks. Another common problem is dislocation of the shoulder. In this case, the top of arm (humeral head) comes out of its normal socket (glenoid cavity). Some people have relatively lax shoulder muscles, and are prone to shoulder dislocations.
nThe Spine
The spine is comprised of 26 vertebral bones. From the top to the bottom, there are 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, the sacrum, and the coccyx. The sacrum is comprised of 5 fused bones, while the coccyx is formed from 4 fused bones. The lumbar section of the spine is shown in the 3-D model above. Each vertebral bone connects to the vertebrae above and below it by two facet joints. There are also fibrous disks that separate the bones of the cervical, thoracic, and lumbar sections of the spine. Interestingly, these tough intervertebral disks have a jellylike core. The facet joints give the spine its flexibility, while the disks cushion the vertebral bones during activities like running or jumping. The transverse and posterior spinous processes are the primary attachment points for the numerous muscles which hold up the spine.
nThe Spine
The spine is comprised of 26 vertebral bones. From the top to the bottom, there are 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, the sacrum, and the coccyx. The sacrum is comprised of 5 fused bones, while the coccyx is formed from 4 fused bones. The lumbar section of the spine is shown in the 3-D model above. Each vertebral bone connects to the vertebrae above and below it by two facet joints. There are also fibrous disks that separate the bones of the cervical, thoracic, and lumbar sections of the spine. Interestingly, these tough intervertebral disks have a jellylike core. The facet joints give the spine its flexibility, while the disks cushion the vertebral bones during activities like running or jumping. The transverse and posterior spinous processes are the primary attachment points for the numerous muscles which hold up the spine.
w
The Lungs
The lungs are a vital organ which enables the body to obtain oxygen from the air we breathe, and to eliminate carbon dioxide. Breathing is accomplished with the chest wall muscles, and the diaphragm muscle, which separates the chest cavity from the abdomen. When the chest cavity expands, the lungs expand with it, drawing air down into the lungs. When the chest cavity relaxes, the lungs shrink, and waste carbon dioxide is expelled. The lungs are not directly attached to the chest wall. Instead they are encased in a double layer membrane called the pleura. One of the pleural layers is firmly attached to the lungs with the other one firmly attached to the chest wall. There is always a small amount of fluid between the two pleural layers which allows them to freely slide over each other.
The lungs are divided into distinct lobes which are supplied by their own airways (bronchi) and their own arteries. On the right side, there are three main lobes called the upper, middle, and lower lobes. On the left, there are only two lobes called the upper and lower lobes. This anatomy is illustrated in the 3-D model above. The fissures that separate the upper and lower lobes on both sides are called the major fissures. The right lung also has a minor fissure that separates the upper and middle lobes. Notice how the minor fissure is nearly horizontal, but the major fissures run at a steep angle. When a doctor listens to the breathing sounds on your back, he or she is listening to the lower lobes, even when the stethoscope is placed high up by the shoulder blades.
One of the disorders sometimes seen in the emergency room is a collapsed lung. Surprisingly, the natural tendency of the lungs is to collapse into a small ball near the center of the chest. They are held in their normal expanded state only by the attraction between the two layers of the pleura. If you have ever tried to separate two sheets of wet glass, then you know how this works. Occasionally, air gets between the two pleural layers, causing them to separate, and the lung collapses. This is called a pneumothorax, meaning air in the thorax (chest cavity). The air can either come from the outside because of a penetrating wound, or from the inside because a part of the lung developed a hole in it. Another problem that is sometimes seen is excess water between the two pleural layers. This is called a pleural effusion, a condition commonly referred to as water on the lung. There are many causes for a pleural effusion, some benign and some quite bad. A pleural effusion is typically treated by sticking a needle or a tube into the chest and draining out the fluid.
w
The Lungs
The lungs are a vital organ which enables the body to obtain oxygen from the air we breathe, and to eliminate carbon dioxide. Breathing is accomplished with the chest wall muscles, and the diaphragm muscle, which separates the chest cavity from the abdomen. When the chest cavity expands, the lungs expand with it, drawing air down into the lungs. When the chest cavity relaxes, the lungs shrink, and waste carbon dioxide is expelled. The lungs are not directly attached to the chest wall. Instead they are encased in a double layer membrane called the pleura. One of the pleural layers is firmly attached to the lungs with the other one firmly attached to the chest wall. There is always a small amount of fluid between the two pleural layers which allows them to freely slide over each other.
The lungs are divided into distinct lobes which are supplied by their own airways (bronchi) and their own arteries. On the right side, there are three main lobes called the upper, middle, and lower lobes. On the left, there are only two lobes called the upper and lower lobes. This anatomy is illustrated in the 3-D model above. The fissures that separate the upper and lower lobes on both sides are called the major fissures. The right lung also has a minor fissure that separates the upper and middle lobes. Notice how the minor fissure is nearly horizontal, but the major fissures run at a steep angle. When a doctor listens to the breathing sounds on your back, he or she is listening to the lower lobes, even when the stethoscope is placed high up by the shoulder blades.
One of the disorders sometimes seen in the emergency room is a collapsed lung. Surprisingly, the natural tendency of the lungs is to collapse into a small ball near the center of the chest. They are held in their normal expanded state only by the attraction between the two layers of the pleura. If you have ever tried to separate two sheets of wet glass, then you know how this works. Occasionally, air gets between the two pleural layers, causing them to separate, and the lung collapses. This is called a pneumothorax, meaning air in the thorax (chest cavity). The air can either come from the outside because of a penetrating wound, or from the inside because a part of the lung developed a hole in it. Another problem that is sometimes seen is excess water between the two pleural layers. This is called a pleural effusion, a condition commonly referred to as water on the lung. There are many causes for a pleural effusion, some benign and some quite bad. A pleural effusion is typically treated by sticking a needle or a tube into the chest and draining out the fluid.
?The Pancreas
The pancreas is an organ with two separate functions. First, the pancreas plays an important role in the digestion of food. The pancreas does this job by making digestive enzymes that are released into the pancreatic duct and then into the small intestine. The pancreatic duct usually joins the common bile duct just before it enters the duodenum at the Ampulla of Vater. The second function of the pancreas is to make hormones that are released into the blood. The hormones released, insulin and glucagon, both play key roles in the regulation of blood sugar levels.
┌The Pelvis
The pelvis serves to support the upper body, and to protect the lower abdominal and pelvic organs. It consists of the two large hipbones and the sacrum. The sacrum is the triangular bone that also forms the lower part of the spinal column. The hipbones are firmly joined to the sacrum in the back and joined to each other in the front. This structure creates a very strong and rigid ring of bone. Each hipbone is composed of three fused bones: the ilium, the ischium, and the pubis. The ilium is a large flat bone similar to the plates of the skull. The ischium is a round, curved bone which supports the weight of the body when sitting. The pubis is a smaller bone similar to the ischium. All three bones (ilium, ischium, and pubis) come together to form the hip socket (acetabulum). The pubic rami come together to join at the pubic symphysis. Symphysis is a word which simply means a joining of two structures. It can also have the more specific meaning of two bones that are joined by a fibrous joint.
There are several notable differences between the male and female pelvis. In men, the pelvis is narrower and heavier; it is built to support a greater body weight. In women, the pelvis is broad and has a larger opening, built to allow childbirth. The pubic symphysis is also less rigid in women, allowing it to stretch and widen during childbirth. When examining the skeletons of human ancestors, anthropologists often use the pelvis to distinguish males and females.
┌The Pelvis
The pelvis serves to support the upper body, and to protect the lower abdominal and pelvic organs. It consists of the two large hipbones and the sacrum. The sacrum is the triangular bone that also forms the lower part of the spinal column. The hipbones are firmly joined to the sacrum in the back and joined to each other in the front. This structure creates a very strong and rigid ring of bone. Each hipbone is composed of three fused bones: the ilium, the ischium, and the pubis. The ilium is a large flat bone similar to the plates of the skull. The ischium is a round, curved bone which supports the weight of the body when sitting. The pubis is a smaller bone similar to the ischium. All three bones (ilium, ischium, and pubis) come together to form the hip socket (acetabulum). The pubic rami come together to join at the pubic symphysis. Symphysis is a word which simply means a joining of two structures. It can also have the more specific meaning of two bones that are joined by a fibrous joint.
There are several notable differences between the male and female pelvis. In men, the pelvis is narrower and heavier; it is built to support a greater body weight. In women, the pelvis is broad and has a larger opening, built to allow childbirth. The pubic symphysis is also less rigid in women, allowing it to stretch and widen during childbirth. When examining the skeletons of human ancestors, anthropologists often use the pelvis to distinguish males and females.
eThe Foot and Ankle
The ankle is a hinge joint connecting the bones of the lower leg (tibia and fibula) and the uppermost bone of the foot (talus). The ankle is held together by several strong ligaments which provide stability and prevent excessive movement. The ankle only allows simple upward and downward motions of the foot. Other foot movements require motion of the joints within the foot itself. Because the ankle is subject to great stress, sprains of the ankle ligaments are very common. Each foot has 26 separate bones. The two largest foot bones are the calcaneus (heel bone), and the talus. Long tendons attach many of the bones of the foot to strong muscles located in the lower leg. These tendons can be seen in the 3-D model shown above.
There are a number of disorders that are frequently seen in the foot. These include corns, bunions, and gout. Corns are small areas of thickened skin usually caused by tight fitting shoes. A bunion is a firm, fluid filled lesion that forms over the base of the big toe. Like corns, bunions are usually the result of wearing tight, pointed shoes. Bunions sometimes require surgical removal and reconstruction of the great toe to prevent them from recurring. Gout is a form of arthritis that commonly affects the joint of the great toe. Gout results from the formation of uric acid crystals within a joint. These crystals cause significant inflammation and pain in the affected joint. A person suffering from an attack of gout in the great toe is generally unable to even stand on the foot. Unlike corns and bunions which are more common in women, gout is 10 times more common in men.
eThe Foot and Ankle
The ankle is a hinge joint connecting the bones of the lower leg (tibia and fibula) and the uppermost bone of the foot (talus). The ankle is held together by several strong ligaments which provide stability and prevent excessive movement. The ankle only allows simple upward and downward motions of the foot. Other foot movements require motion of the joints within the foot itself. Because the ankle is subject to great stress, sprains of the ankle ligaments are very common. Each foot has 26 separate bones. The two largest foot bones are the calcaneus (heel bone), and the talus. Long tendons attach many of the bones of the foot to strong muscles located in the lower leg. These tendons can be seen in the 3-D model shown above.
There are a number of disorders that are frequently seen in the foot. These include corns, bunions, and gout. Corns are small areas of thickened skin usually caused by tight fitting shoes. A bunion is a firm, fluid filled lesion that forms over the base of the big toe. Like corns, bunions are usually the result of wearing tight, pointed shoes. Bunions sometimes require surgical removal and reconstruction of the great toe to prevent them from recurring. Gout is a form of arthritis that commonly affects the joint of the great toe. Gout results from the formation of uric acid crystals within a joint. These crystals cause significant inflammation and pain in the affected joint. A person suffering from an attack of gout in the great toe is generally unable to even stand on the foot. Unlike corns and bunions which are more common in women, gout is 10 times more common in men.
BThe Arm
The elbow is the hinge joint which connects the lower end of the humerus with the upper ends of the radius and ulna. The elbow permits the arm to be bent by the powerful biceps muscle and then straightened by the triceps muscle. The biceps and triceps thus form a pair of muscles which have opposite actions. It is a general rule that the muscles of the body are organized into pairs or groups which have opposite actions.
The elbow also allows the forearm to be rotated without moving the upper arm. This is very important for some actions such as turning a door knob. This rotation motion is called either supination or pronation. Supination is the action of turning the palm face up when the arm is held straight out, away from the body. Pronation is the action of turning the palm face down when the arm is held straight out. Following the general rule, these important movements are accomplished by a pair of muscles with opposite actions. The words supination and pronation are related to the words supine, which means to lie face up, and prone, which mean to lie down face down.
Repetitive motions can strain the tendons of the elbow and cause pain. Tennis elbow and golfers' elbow are common conditions resulting from overuse and strain of the elbow tendons. Most everyone has felt the pins and needles sensation caused by hitting the tip of their elbow. This is often referred to as hitting the "funny bone." The temporary pain is caused by impingement of the ulnar nerve which travels through a narrow groove, close to the surface of the skin, as it passes over the elbow.
BThe Arm
The elbow is the hinge joint which connects the lower end of the humerus with the upper ends of the radius and ulna. The elbow permits the arm to be bent by the powerful biceps muscle and then straightened by the triceps muscle. The biceps and triceps thus form a pair of muscles which have opposite actions. It is a general rule that the muscles of the body are organized into pairs or groups which have opposite actions.
The elbow also allows the forearm to be rotated without moving the upper arm. This is very important for some actions such as turning a door knob. This rotation motion is called either supination or pronation. Supination is the action of turning the palm face up when the arm is held straight out, away from the body. Pronation is the action of turning the palm face down when the arm is held straight out. Following the general rule, these important movements are accomplished by a pair of muscles with opposite actions. The words supination and pronation are related to the words supine, which means to lie face up, and prone, which mean to lie down face down.
Repetitive motions can strain the tendons of the elbow and cause pain. Tennis elbow and golfers' elbow are common conditions resulting from overuse and strain of the elbow tendons. Most everyone has felt the pins and needles sensation caused by hitting the tip of their elbow. This is often referred to as hitting the "funny bone." The temporary pain is caused by impingement of the ulnar nerve which travels through a narrow groove, close to the surface of the skin, as it passes over the elbow.
âAlveoli
The alveoli are the tiny air sacs in the lungs where red blood cells pick up oxygen, and release the waste product carbon dioxide. The photograph above shows several alveoli. Note the thin alveolar walls. The red blood cells are contained within tiny pulmonary capillaries that course through the alveolar walls. The red blood cells tend to flow in single file lines through the pulmonary capillaries. Because of the thin walls, the red blood cells come into very close contact with the air. Both of these things promote efficient transfer of oxygen and carbon dioxide between the red blood cells and the air within the alveoli.
Under normal circumstances, the alveoli form an enormous surface area for gas exchange to take place within the lungs. However, there are many diseases which disrupt this process. Heart failure is one which causes some of the alveoli to fill up with water, preventing air from getting near the red blood cells. Pneumonia causes a similar problem by filling up some of the alveoli with pus. Over time, cigarette smoking can also seriously damage the alveoli, leading to a disease called emphysema. In this case, it is the alveolar walls which are injured. Eventually, large segments of alveoli disappear entirely, leaving behind air pockets called bullae. No gas exchange occurs in these large air pockets in the lungs, and patients can become quite short of breath.
Alzheimer's Disease
Alzheimer's disease is a progressive brain disorder in which brain cells degenerate and the brain substance shrinks. The picture above shows the appearance of a brain from an Alzheimer's patient. Note how the folds are much more open than in a normal brain. The progressive nature of the disease causes patients to become increasingly forgetful and disoriented as time goes by. It is by far the largest cause of dementia in elderly people, but its cause remains unknown. There is no treatment for Alzheimer's disease beyond caring and appropriate support for those suffering from the disease. It is important to look for other causes in patients suffering from dementia, however, since approximately 10% of elderly people will prove to have some other treatable cause for their symptoms.
^Amniocentesis
Amniocentesis is a diagnostic procedure in which a small volume of fluid is withdrawn from the amniotic sac. The amniotic sac is the membrane within the uterus that surrounds the fetus. This procedure is done quite carefully while watching the tip of the needle with ultrasound. The amniotic fluid contains fetal cells which can be grown and then analyzed. In particular, doctors and patients are interested in analyzing the chromosomes (DNA) of the developing fetus. Amniocentesis can only be performed between the 16th and 18th weeks in pregnancy. Also, the chromosome test takes about 2 to 4 weeks so its results may not be available until the 20th week. This is well into the second trimester. There is a slight increased risk of miscarriage (0.5%) as a complication of amniocentesis. It is generally only recommended for women over 35, who are all at a somewhat higher risk for having a child with Down's syndrome, or women who are at risk for having a genetically abnormal baby for some other reason. Another technique similar to amniocentesis is called chorionic villous sampling (CVS). This test involves using a needle to obtain actual cells from the chorion which surrounds the fetus, rather than just amniotic fluid. CVS can be performed much earlier in pregnancy, at about 12 weeks, but it has a higher risk (about 1-2%) of inducing a miscarriage.
Angina
When atherosclerosis affects the coronary arteries, it is called "coronary artery disease" (CAD). Patients with CAD experience chest pain when the blood supply to the heart is inadequate to meet the demand for oxygen. This pain is called "angina." CAD is a very common ailment with characteristic symptoms. Angina typically occurs after a predictable amount of exercise (e.g., walking up a flight of stairs), and is relieved by rest. Medication is available that relieves the pain by briefly dilating the coronary arteries, but this has no effect on the underlying disease. Patients with angina are at high risk for having a heart attack if their coronary artery disease is not treated.
The incidence of atherosclerosis is very strongly correlated with a number of risk factors. Three of the major risk factors are a diet high in fat and cholesterol, cigarette smoking, and inactivity. Fortunately, the progression of atherosclerosis can be significantly slowed, and sometimes even reversed, by modification of these lifestyle choices.
)Antibodies
This picture shows several Y-shaped antibody molecules within a blood vessel. Antibodies are made by the immune system to react with specific foreign invaders. Bacteria, viruses, and other microorganisms are all common pathogens that will usually elicit an antibody response. Once made, antibodies stay in the circulation for many years -- in some cases, even a whole lifetime. If an individual is re-exposed to a pathogen for which they have previously made antibodies, they will be able to eliminate the pathogen before it causes any problems.
╡Sports Injuries
There is a wide range of injuries that may result from athletic activity. Fractures, ligament sprains, muscle strains, and cartilage tears are just some of the injuries commonly encountered in the emergency room. The ankle is the joint most frequently sprained. This typically occurs when the ankle "turns over" and the ligaments are severely stretched. An x-ray is usually taken to exclude the possibility of a fracture. An ankle sprain causes significant pain and swelling. Treatment consists of ice-packs to reduce swelling during the first 24 hours, analgesics to relieve pain, and rest while the joint heals itself. Strain of the Achilles tendon, located at the back of the ankle, is another injury sometimes encountered.
Knee injuries are also commonly encountered in the emergency room. Football and skiing are two sports which place particularly great stress on the knees. Twisting motions can lead to serious ligament sprains, and/or tearing of the cartilage cushions (menisci) in the knee. Magnetic resonance imaging (MRI) and arthroscopic surgery have revolutionized the treatment of these injuries. With MRI it is often possible to determine the exact nature of the joint injury from the images alone. The orthopedic surgeon may then be able to repair the knee using arthroscopic surgery without ever having to open up the joint. The picture above shows a surgeon performing arthroscopic surgery. This technique involves placing an endoscope (a small, flexible, lighted viewing tube) into the joint through a small incision. Other tools such as tiny scissors or scalpels are also placed into the joint through small incisions. The surgeon then performs the operation with these tiny tools while watching what he or she is doing on a television screen. Like the knee, shoulder injuries are also frequently treated with arthroscopic surgery.
Muscle strains are another common injury that may result from vigorous athletic activity. Running, golfing, and tennis are all examples of activities that will sometimes cause strain of muscles or their tendons. Like ligament sprains, muscle strains are treated with ice packs to reduce swelling, analgesics to relieve pain, and rest to promote healing.
░Asthma
Asthma is a common illness, affecting about 1 in 20 people in the United States. There are two main types of asthma: extrinsic asthma, in which an allergen or some other external stimulus is responsible for attacks, and intrinsic asthma, in which there is no apparent cause for attacks. With either type, the main problem is inflammation and narrowing of the bronchioles. The inflammation leads to increased sputum production in the bronchioles which further narrows the airways. During an asthma attack, patients experience wheezing and extreme shortness of breath. Bronchodilators are the mainstay of therapy, once an attack has started. These medicines cause the narrowed airways to open up and allow more air in and out. The photograph above shows a patient using an inhaler containing a bronchodilator. Anti-inflammatory medicines are also an important part of therapy. These medicines are used to try to prevent asthma attacks.
SOn the Tip of a Pin
Bacteria are remarkably small. The photograph above demonstrates their size relative to the tip of a pin. The immune system is usually adequate to allow recovery from exposure to bacterial illness. The advent of antibiotics, however, has revolutionized the treatment of serious bacterial illness that has not been controlled by the immune system. These medications work either by killing bacteria directly, or else by stopping their growth in order that the immune system can more effectively eliminate them. Unfortunately, bacteria frequently develop resistance to the antibiotics which once killed them. In effect, a war has begun between the scientists that keep developing new antibiotics and the bacteria which seem to develop resistance to those antibiotics at an ever increasing rate. The most simple explanation for emerging resistance is selection pressure. If only one in a large number of bacteria is resistant to a drug, then all the other organisms will be killed, and the resistant cell will multiply to replace the dead bacteria. This process occurs because bacterial reproduction is so rapid, occurring about once every 20 minutes. After 6 hours, a single bacterium can regenerate a population of a million. This is a strong argument against the indiscriminate use of antibiotics which only leads to more and more resistant strains.
!Bacteria
Bacteria are a very large group of single-cell microorganisms. Bacteria were first discovered with the advent of the microscope in the 17th century. However, it was not until Louis Pasteur studied them in the mid-19th century that it became clear that bacteria were responsible for many human diseases. The picture above shows a single bacterium of the salmonella type. This bacteria often causes fever and diarrhea in humans. Note that it has a thick capsule, and flagella (hair-like structures) that it uses to move around. There are many ways to classify bacteria. One method is based on shape, of which there are three main classes. Cocci are spherical, bacilli are rod-shaped, and spirilla are spiral-shaped. Bacteria are also classified as being either gram positive or gram negative, based on whether they take up the gram stain that is commonly used to make them easier to see under the microscope. A third method of classification is whether they can live in the presence of oxygen (aerobic) or require the absence of oxygen (anaerobic).
MBall and Cage Valve
The second most common major heart operation in the western world is valve replacement. Any one of the four heart valves may become either so tight, or so leaky that it needs to be replaced in order to restore normal heart function. As a rule, valve replacement surgery has a very high success rate. Long term complications from rheumatic fever are still the most frequent cause of severe valve malfunction.
Many different types of artificial heart valves have been devised over the years. The picture above shows a mechanical ball and cage valve which has been widely used. Another popular mechanical valve uses either one or two tilting disks. It is also common to use tissue valves taken from pigs (porcine valves). Least commonly, valves can be taken from human organ donors. Mechanical valves last longer than porcine or human tissue valves, making them more suitable for younger patients. On the other hand, mechanical valves damage red blood cells more than tissue valves do, and they tend to cause the formation of blood clots. Because of this, all people with mechanical valves need to take anticoagulant medication (blood thinners) to prevent blood clots from forming. The choice of what type of artificial valve to use is thus a difficult question that must be decided for each individual requiring a valve replacement operation.
FBlood Cells
There are three main types of cells within the blood. These are shown in the picture above. From left to right, the picture shows a platelet, a white blood cell, and a red blood cell. The sizes are not to scale. A white blood cell is actually much larger than a red blood cell, and a platelet is much smaller than a red blood cell. Red blood cells are the most numerous by far, making up about 40% of the total blood volume. White blood cells and platelets are much less numerous, together making up only about 5% of the blood by volume. The remaining half of the blood is composed of a fluid called plasma.
Plasma is a sticky fluid that is 95% water. The other 5% is composed of the many substances that are dissolved within the plasma. These include nutrients, proteins, waste products, and hormones. Nutrients are the substances needed by the body's tissues to sustain their normal function. The principal nutrients are sugars, fats, amino acids, vitamins and minerals. All of these are dissolved within the plasma, and then delivered to each cell within the body. The primary proteins in the plasma serve either as part of the clotting mechanism, as part of the immune system, or as transporters for nutrients. The main waste product in the plasma is urea. It is a by-product of metabolism that is transported to the kidneys where it is eliminated. Hormones are chemicals that are used to regulate many of the body's functions. They are produced by the body's endocrine glands, and then released into the blood so that they may travel to their target organs elsewhere in the body.
ùBlood Bank
One of the great breakthroughs in the history of medicine was Karl Landsteiner's discovery of blood groups in 1901. Prior to this discovery, blood transfusions were hazardous at best, and oftentimes lethal. Landsteiner discovered two basic markers (antigens) that are often present on the surface of red blood cells. He named these two antigens A, and B. All people are either type A, type B, type AB, or type O; depending on whether they have one, both, or neither of these markers on their red cells. Landsteiner also discovered that plasma usually contains antibodies that can react with the A and B antigens on the red blood cells. Before giving a blood transfusion, it is necessary to determine that the recipient's plasma does not have any antibodies that will react with the donor's red blood cells.
These days, blood transfusions are very safe, and transfusion reactions are virtually unheard of. The more significant risk today is the transmission of a disease such as hepatitis or AIDS through a blood transfusion. This risk is very small, however, since all donor blood is carefully screened to make sure it is free from these infectious viruses. Nonetheless, it has become a common practice to donate one's own blood in advance of a scheduled operation, so that the chance of contracting an illness is reduced to zero. It is important to remember that blood can only be obtained from human donors. Donating blood is a very helpful thing that people can do for their fellow men and women. Also, it is good to bear in mind that it is impossible to contract any illness by donating blood. The picture above shows several units of blood packaged for transfusion.
≤The Human Brain
The largest and most developed part of the human brain is the cerebrum. The two massive cerebral hemispheres account for more than 70% of the weight of the entire brain. The photograph of a human brain shown above is dominated by the cerebrum, with its many deep folds. Also seen in the photograph are the cerebellum, located at the back of the brain, and the brainstem. The brain and the spinal cord together form the central nervous system (CNS). The CNS is the control center for the body. It gathers information about the environment and the body from the peripheral nervous system and then initiates appropriate actions.
The brain and spinal cord are surrounded by three membranes (meninges). The two outermost membranes (the dura and the arachnoid) are separated from the inner membrane (the pia) by a space filled with fluid. This fluid is called cerebrospinal fluid (CSF). The brain makes about 500 milliliters (1 pint) of CSF each day. The CSF bathes the brain and acts as a cushion for the brain during movement of the head. Lumbar puncture is a safe and common test done to examine the CSF. This test is done by placing a needle into the spinal canal, low in the back, below the end of the spinal cord. CSF can then be withdrawn from the spinal canal. CSF is normally a clear fluid, but it may become cloudy when there is an infection of the meninges.
Emerging from the brainstem are 12 pairs of cranial nerves. The cranial nerves are responsible for all of the functions of the head. These include such things as smell (cranial nerve 1), vision (cranial nerve 2), eye movements (cranial nerves 3, 4, & 6), facial sensation (cranial nerve 5), facial expressions (cranial nerve 7) hearing and balance (cranial nerve 8), taste (cranial nerve 9), and tongue movements (cranial nerve 12). Cranial nerves 10 and 11 are atypical. The 10th cranial nerve leaves the head and travels downward to all the major organs of the body where it influences their activity. Because of its wandering course, it is called the vagus nerve. The 11th cranial nerve also leaves the head, but it only travels as far as the neck where it helps direct neck movements. The skull has many little holes in its base which allow all the cranial nerves to travel to their destinations.
ëBrain Regions
Most brain functions have been found to be controlled by very specific regions of the brain. Voluntary movements are controlled by a part of the frontal lobes (the pre-central gyrus). Sensation is processed by an adjacent part of the brain in the parietal lobes (the post-central gyrus). Interestingly, the nerve pathways for both movement and sensation cross the midline. This causes the right side of the brain to control the left side of the body, and the left side of the brain to control the right side of the body. Most people have a dominant left brain, and are thus right handed. The right and left sides of the brain communicate across a large fiber tract called the corpus callosum. In a few rare cases, the corpus callosum has been cut surgically to control the spread of seizures from one side of the brain to the other. This can result in very unusual symptoms. An example is being unable to name an object held in the left hand because the signals can't cross back over to the left brain where the speech center is.
Speech is an important function controlled by two main regions of the brain, Broca's area and Wernicke's area. Broca's area is in the frontal lobe and is responsible for generating meaningful speech. People who sustain damage in Broca's area are often unable to say anything that makes sense, even though they are able to understand other people. Wernicke's area is necessary for speech recognition. Damage to Wernicke's area results in an inability to comprehend spoken language, a very disabling condition to be sure. Interestingly, the two speech centers are confined to only one side of the brain, typically the dominant left side. This is different then most brain functions which are handled by the analogous brain regions on both sides. Another important function of the brain is vision, which surprisingly, is processed at the very back of the brain in the occipital lobes.
(Newly Born
Breast-feeding is the natural method of feeding infants. It was, of course, perfected long before people ever came up with the idea of baby formula. Today, most doctors agree that breast milk provides the newborn infant with the ideal balance of nutrients. It also provides the baby with antibodies from the mother which help to prevent infections until the baby's immune system becomes stronger after a few months. There can be problems with breast-feeding including sore or cracked nipples, but these problems can usually be resolved without stopping breast-feeding. However, there are a number of legitimate reasons to choose bottle-feeding rather than breast-feeding. The choice not to breast-feed is one that a woman should make after consultation with someone knowledgeable about the subject.
≥Breech Babies
By the eighth month of pregnancy, most babies have assumed a head-down position. If the baby is not head down, then it is said to be in a "breech" position. It is sometimes possible to move a baby into the head-down position by pushing from the outside. If this is not successful, then the baby will often remain in the breech position throughout the remainder of the pregnancy and delivery. Breech deliveries are more difficult for both the baby and the mother because the baby's body does not mold a path through the pelvis as well as the head normally does. Some doctors will try to deliver a breech baby vaginally, while others prefer to perform a caesarean section for breech babies because it poses less risk to the mother and to the baby.
gThe Breast
The primary function of the female breast is to produce nourishing milk for a newly born baby. The female breast is well suited for this job. It consists of 15 to 20 lobes of milk secreting glands that are embedded in fatty tissue. The milk glands all empty into a network of ducts that exit the breast at the nipple. The production of milk is called "lactation." Lactation is maintained after delivery by the hormone prolactin, which is secreted by the pituitary gland. The breast contains no muscles. Instead, it is held up by fine ligaments that connect to the skin in front and the chest wall behind.
<Brain MRI
The images produced by modern magnetic resonance imaging (MRI) scanners are exquisite in their appearance. The picture above shows an image of the brain as seen with MRI. It reveals the underlying anatomy in detail previously only seen by pathologists working with anatomic specimens. The availability of this technology has significantly affected the practice of medicine. Many diseases are now readily diagnosed on the basis of MRI exams alone. On the other hand, their is still no substitute for sensible clinical judgement and a friendly, caring bedside manner.
₧Broken Bones
Fractures of the arm or leg are relatively common. An x-ray is usually taken when a fracture is suspected. X-rays were first discovered in 1896 by Wilhelm Conrad Roentgen. Each of the body's tissues absorbs x-rays in a predictable way. The bones are dense and absorb x-rays much better than the soft tissues, which are mostly made of water. An x-ray of the arm or leg is performed by placing the extremity between a piece of film and a tube which makes the x-rays. The x-ray tube is then turned on for a brief moment to expose the film. The bones absorb most of the x-rays, and thus appear white on the film. In contrast, most of the x-rays penetrate through the soft tissues to expose the underlying film and turn it dark grey. A radiologist then examines the film to determine if there is a fracture of one of the bones. A fracture is seen as a break in the normally smooth contour of one or more of the bones.
ªThe Small Airways
The small airways consist of the bronchioles and the alveoli. Structurally, the bronchioles are different from the larger bronchi because they lack cartilage within their walls. The terminal bronchioles are the smallest airways within the lungs. At their end, they branch into many small, grape-like sacs called "alveoli." The illustration above shows three clusters of alveoli branching from a terminal bronchiole.
±Coronary Bypass Grafting
The most common major heart operation in the Western world is coronary artery bypass grafting (CABG). Approximately 500,000 CABG operations are currently performed in the U.S. each year. This operation is recommended for treatment of severe coronary artery disease that is unsuitable for treatment with coronary angioplasty. The operation involves taking a blood vessel from the leg (saphenous vein), and using it to make new coronary vessels that bypass the narrowed segments of the patient's diseased coronary arteries. It is also typical to redirect one of the arteries from the chest wall so that it will supply the heart muscle instead. The illustration above shows a heart after several new coronary bypass grafts have been sewn in place.
)Atherosclerosis
Atherosclerosis is a disease which results in narrowed arteries and decreased blood flow. The arteries become narrowed because of a build-up of plaques within their inner walls. The picture above shows a yellow plaque within the inner layer of an artery. Plaques consist of a mixture of substances including cholesterol, fat, fibrous tissue, clumps of platelets, and sometimes calcium.
Atherosclerosis begins early in life, but generally causes no symptoms until middle or old age. This is because it takes many years for plaques to develop, and because normal arteries are much larger than they need to be. Only after an artery becomes very narrowed will blood flow be diminished enough to cause symptoms. When atherosclerosis affects the arteries supplying blood to the heart, patients experience intermittent pain called "angina." Likewise, when the arteries supplying blood to the legs are affected, patients experience intermittent leg pain called "claudication." Both angina and claudication are brought on by activity and are relieved with rest.
Cardiac Muscle
Cardiac muscle is found only in the heart. Cardiac muscle has the unique property of rhythmically contracting on its own without requiring any direct instructions from the brain. The brain, acting through the autonomic nervous system, serves only to influence the rate at which the heart contracts. Interestingly, heart transplants work only because the heart is able to contract without direct instructions from the brain. After a heart transplant, there is no connection between the brain of the recipient and his or her new heart.
aThe Large Airways
The large airways include the trachea (windpipe) and the bronchi. The first branching point in the respiratory tree is called the carina. The trachea divides at the carina to form the right and left mainstem bronchi which each enter one of the lungs. The photograph above shows the carina. The mainstem bronchi then divide to form the lobar bronchi. There are three lobar bronchi on the right side (upper, middle, and lower) and two on the left (upper and lower). The lobar bronchi go on to divide again and again into even smaller bronchi.
The photograph above was taken with an instrument called a bronchoscope. Like the endoscopes used to study the digestive system, the bronchoscope has a light and a camera lens at its end. It is different, however, since it is straight and rigid rather than flexible. The bronchoscope is most frequently used to look at the inside of the airways in order to help make a diagnosis. Surgical tools can also be manipulated through the bronchoscope, enabling direct treatment of some medical problems. Another common use of the bronchoscope is to pull out foreign bodies which have been accidently breathed in. Of interest, most foreign bodies wind up in the right lung because the right mainstem bronchus takes a relatively straight path down from the trachea, while the left mainstem bronchus branches at a sharper angle.
The Carpal Tunnel
The median nerve and the flexor tendons for the phalanges all travel through a narrow space in the wrist called the "carpal tunnel." The roof of the carpal tunnel is formed by a ligament called the "flexor retinaculum" which connects the carpal bones at the front of the wrist. Carpal tunnel syndrome occurs when repetitive hand and wrist motions cause swelling of the flexor tendons and squeezing of the median nerve. This impingement of the median nerve is the primary cause of the pain associated with carpal tunnel syndrome. Surgical treatment involves cutting the ligament which forms the roof of the carpal tunnel. This makes extra space and frees up the median nerve. Carpal tunnel syndrome can also be treated with braces which prevent excessive wrist motion.
ÉStudying the Heart
As a first step in the evaluation of patients with coronary artery disease (CAD), it is desirable to study the coronary arteries. Many different tests have been devised to do this. Some of these tests are simple and non-invasive like the stress EKG test. This test requires only that the patient exercise while being monitored with an EKG machine. The accuracy of this test is further improved if pictures of the heart are taken with a nuclear medicine camera during exercise and after resting. At present, the definitive test for evaluating the coronary arteries is angiography. Coronary angiography is an invasive test that requires placing a catheter in the coronary arteries. Dye is then injected, and detailed pictures of the coronary arteries are obtained. This test enables doctors to determine the exact location and severity of the plaques within the coronary arteries.
Several new forms of treatment for CAD have emerged in recent years. The most well accepted is coronary angioplasty which was first introduced in 1976. Coronary angioplasty involves positioning a small balloon catheter in a coronary artery such that the balloon spans a significant plaque. The balloon is then inflated to compress the fatty plaque and make it smaller. When the balloon is deflated, the plaque usually remains compressed. This increases the size of the arterial lumen (central opening), and improves blood flow to the heart. Other techniques for treating CAD utilize tiny catheters with either cutting blades to physically remove the plaque material, or lasers to vaporize the plaque material. Neither method has yet advanced to the stage of widespread acceptance.
÷First Steps
By a year of age, babies have generally mastered crawling and have begun walking around furniture while holding on (cruising). They may also be starting to take their first steps. Some babies are proficient walkers at this age, a skill that parents may soon find is a bigger problem than they had imagined. Twelve-month-old babies can grasp small objects and release them easily. Both hands are generally used without obvious preference. At this stage, objects are more likely to be dropped on purpose and then picked up once again rather than being placed in the mouth. Babies at this age will turn when their name is called and they begin to show some understanding of language. These babies will also demonstrate affection with familiar adults.
≡I Found My Toes
Children acquire physical and motor skills in specific stages called "milestones." There are, of course, wide variations between individuals, but general guidelines are useful to assess development. By six months, babies can usually roll over, and they can sit up with support. They are able to track objects with their eyes, and reach out toward those objects. Once grasped, objects may be transferred from one hand to the other, or brought to the mouth. One of the best things babies do at sixth months of age is smile in response to their parents' voices, and sometimes they laugh and chuckle. Babies at this stage of development also enjoy looking at themselves in a mirror or looking at other babies. Peek-a-boo is often a favorite game.
╞Chromosomes
The photograph above shows the 23 pairs of chromosomes that are obtained from a normal amniocentesis. The collection of chromosomes, arranged in this way, is called a karyotype. This particular individual will be a male because there is both an X and a Y chromosome. All males have an X and a Y chromosome, while all females have two X chromosomes. This means that all egg cells (ova) will have an X chromosome since that is all they can get from the mother. On the other hand, half of the sperm cells produced by a man will contain an X chromosome while the other half will contain a Y chromosome. The sex of a new individual, male or female, is determined by whether the ovum is fertilized by an X or a Y sperm cell. There are other things besides the sex of the developing fetus that can be learned from the karyotype. The most commonly seen abnormality is three copies of the 21st chromosome. This abnormality causes Down's syndrome, also known as trisomy 21. Other abnormalities including trisomy 13 and trisomy 18 can occasionally be seen. The numerous remaining possible genetic abnormalities are likely so severe that development would never get far enough along for an amniocentesis to be performed.
<Cirrhosis
The liver is perhaps the most robust of all the body's organs. As much as three-quarters of the liver can either be removed or destroyed, and the remaining liver cells will grow to replace the whole liver once again. It is possible, however, to damage the liver through repeated exposure to toxic chemicals. The most common example is alcohol abuse. Alcohol is a chemical that is toxic to the body in large doses. The liver detoxifies the alcohol and removes it, but not without damage to the liver itself. Heavy alcohol consumption over many years eventually leads to liver failure. This is called "cirrhosis." The illustration above shows a cirrhotic liver with a close-up of a small section. The other major cause of cirrhosis is chronic hepatitis, due to infection of the liver with one of the hepatitis viruses.
ûColon Cancer
Colon cancer is one the most common types of cancer in the U.S. Although there is no single cause for colon cancer, there are two factors that appear to play a large role. These factors are diet and inheritance. The picture above shows the colon along with a number of chromosomes to illustrate the fact that inheritance plays a role in the development of colon cancer. Diet, however, appears to be the biggest factor. Rates of digestive tract cancer vary widely in different part of the world. In China, cancer of the esophagus is quite common while this is disease is very uncommon in the U.S. In Japan, there is a high rate of stomach cancer, another disease that is rare in the U.S. In contrast, the most common digestive tract cancer in the U.S. by far is cancer of the colon. These findings implicate dietary differences as a cause of digestive tract cancers. Most doctors and scientists believe that it is the high fat, low fiber western diet that is to blame for the high incidence of colon cancer. Like other forms of cancer, the prognosis for colon cancer is relatively good if it is discovered early, before it has spread to other parts of the body.
ƒThe Colon
The colon consists of four main segments: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The appendix is a small, finger-like extension from the cecum, which is in turn part of the ascending colon. The primary role of the colon is to resorb the fluid from the watery mixture that is left over after the small intestine has completed absorbing all the useful nutrients.
πInside the Colon
The picture above shows the inside of the colon as taken with an endoscope. The walls of the colon contain three longitudinal (lengthwise) bands of muscle that create a purse string appearance. These periodic indentations in the wall of the colon are called "haustra." The haustra are clearly seen in the image above. Endoscopy of the colon is performed to allow direct visualization of the colon lining. If anything of concern is sighted, a biopsy will generally be obtained.
ñCrohn's Disease
Crohn's disease is an inflammatory disease that can affect any part of the digestive tract from the mouth to the anus. It is a serious problem that causes many symptoms including pain, fever, diarrhea, and weight loss. The most common site of involvement is the terminal ileum where the small intestine joins the large intestine. The inflammation generally becomes quite severe, sometimes even causing holes (fistulae) to develop in the walls of the intestine. Crohn's's disease tends to be patchy in its involvement of the intestine, with areas of disease interspersed with regions of normal intestine. Treatment for Crohn's disease is directed at relieving the inflammation. This is usually successful at controlling the disease. There is neither any known cause for the disease, nor any definite cure. Surgery to remove affected segments of the digestive tract is always a last resort because the disease tends to recur in other segments.
A related inflammatory bowel disease is Ulcerative colitis (UC). UC is different than Crohn's disease in a few important ways. It only affects the colon, sparing the remainder of the digestive system. It affects continuous segments of the colon so there is never interspersion of normal and diseased intestine. Only the inner lining becomes inflamed with UC, whereas the full thickness of the intestinal wall is affected with Crohn's disease. Treatment is about the same, however, with medicines directed at reducing the inflammation. Of special note, people with UC are at high risk of developing colon cancer, and they must be screened regularly. Sometimes, it is prudent to simply remove the colon to prevent colon cancer from occurring.
mCT Scan
Two new techniques have been developed over the last twenty years that have revolutionized the diagnosis of brain diseases. The first of these to be developed was computed (axial) tomography. This technique is popularly known as either CAT scanning or CT scanning. The first CT scanner came into operation in 1972 in London, England. During the exam, the patient lies with their head in a large device that has a doughnut like opening. The device is basically a sophisticated x-ray tube that is able to spin around the patient and take pictures of the head from every angle. In the most modern CT scanners, the x-ray tube itself doesn't even need to move. Instead, the x-ray beam is simply deflected so that it travels in a full circle around the patient. With either type of CT scanner, a powerful computer is then used to put all the data back together to form detailed images of the brain. Of note, CT scanning is quite general, and any other part of the body can also be scanned. CT scanning is particularly useful because it can be performed so rapidly. Only a few minutes are required to complete the examination.
¢Chest X-Ray
The picture above shows a standard x-ray of the chest. The heart is a relatively dense structure which shows up as a white shadow in the middle of the chest. In contrast, the lungs are filled with air. The air doesn't stop many of the x-rays from reaching the film behind the patient. The lungs thus show up as dark structures. Despite its simplicity, or perhaps because of it, the chest x-ray remains one of the most useful screening tests in medicine. The size of the heart is easily seen on the chest x-ray, a valuable piece of data which implies much about the function of the heart. Also, it is relatively easy to see whether there are any obvious problems with the lungs such as pneumonia. This condition is easy to diagnose because the affected parts of the lungs become more dense and show up as whiter on the x-ray. In serious cases of pneumonia, the alveoli tend to fill up with water and cellular debris. This may render them entirely white on the x-ray. When the alveoli fill up with water, it prevents the red blood cells from picking up oxygen and causes hypoxia. Hypoxia merely means low oxygen. This is the main problem for patients with pneumonia.
╧Defibrillator
When the pattern of the heart beat isn't normal, it is called an arrhythmia. Most arrhythmias produce strikingly abnormal EKG tracings. One interesting group of arrhythmias is caused by a block in the heart's normal conduction pathway. Fortunately, this does not stop the heart completely since there are always some cells below the level of the block that take over the role of initiating the heart beat. The new pacemaker cells tend to beat too slowly, however, so this isn't really a solution. Definitive treatment for a heart block arrhythmia thus requires placement of a battery powered pacemaker. The pacemaker can then be programmed to initiate the heart beat at any desired rate.
The most severe arrhythmia is ventricular fibrillation. A heart in ventricular fibrillation just quivers, and it is unable to pump blood. Effective treatment depends on shocking the heart to get all the muscle cells to begin contracting again in an orderly fashion. The machine used to deliver the shock is called a defibrillator. The paddles from a defibrillator are shown in the picture above. The power of the shock is quite great, and it is very important that all the bystanders stay clear when the defibrillator is used.
╧Mental Health
The brain is the most complex organ, and it is the focus of much medical research. One of the many fields of research involving the brain is mental illness. Serious mental illnesses such as depression and schizophrenia are remarkably common disorders of the brain. Depression affects approximately 10 - 15% of people at some time during their lives. Schizophrenia is estimated to affect just under 1% of the world's population. These numbers make for quite a few cases. There are as many as 1.5 million U.S. citizens with schizophrenia at any one time.
Schizophrenia usually begins between the ages of 15 and 25. The symptoms often appear when a young adult leaves home for the first time to live on his or her own. The illness is equally prevalent in males and females. It is a common misconception that schizophrenia is the same thing as multiple personality disorder, but the ailments are actually quite unrelated. Multiple personalities, as in the story of Dr. Jekyll and Mr. Hyde, is an extremely rare disorder. Schizophrenia is a psychotic illness characterized by profound disturbances in thought and behavior. Patients frequently experience both delusions and hallucinations. Delusions are false ideas that have no reasonable basis in fact (for example, I am invisible). Hallucinations are sensory experiences that occur without any external stimulus. Schizophrenics often feel as if they are being controlled by other forces, such as someone on the television set. The causes of schizophrenia remain incompletely understood. Inheritance definitely plays a significant role. For instance, the identical twin of a patient with schizophrenia has a 50% chance of also having the disease, even if they were raised apart.
Dialysis
The primary functions of the kidneys are to maintain the fluid and salt balance in the blood, and to remove waste products. These jobs are quite essential. If the kidneys fail for any reason, wastes start to accumulate, and the body becomes overloaded with fluid. Fortunately, this problem can be treated with an artificial kidney machine that can be hooked up to the patient when needed. This process is called "dialysis." Usually, patients will undergo a three-hour hemodialysis session about three times a week. The picture above shows a man leisurely reading while receiving dialysis. Kidney transplants are another method for treating people whose kidneys have stopped working. Diabetes is the most common cause of kidney failure that ultimately requires treatment with dialysis.
\DNA Replication
The basic structure of DNA is the double helix. The double helix is formed from two individual strands that complement each other perfectly. In fact there are only four main building blocks, referred to as A, T, G, and C. An A block always pairs with a T block and a G block always pairs with a C block. This remarkably simple structure makes it easy to see how DNA is replicated. An enzyme called DNA polymerase merely needs to separate the two strands of the parent double helix, and then use each strand as a template for a new daughter double helix. Although all the information is contained in each single strand, the double helix does offer redundancy that makes it vastly easier to repair errors when they occur.
DNA can also be copied to make a related molecule called RNA. RNA is the messenger molecule that carries the DNA information out of the nucleus and into the cell for action. The process of copying DNA into RNA is called transcription. The RNA is then used to direct the synthesis of proteins. Unlike DNA and RNA which only use four unique building blocks (bases), proteins are made using 20 unique building blocks called amino acids. To specify the 20 unique amino acids using only the four bases available to either DNA or RNA, simple math tells us that it must require a group of three bases (a triplet). This provides for 64 (four cubed) different triplets that can be made from the four bases. There is a code that states which of the 20 amino acids goes with each of the 64 different RNA triplets. The process of using the RNA to direct the synthesis of proteins is called translation.
ΦDNA
DNA is the molecule which contains all the information for life. It can be thought of as a blueprint or an instruction manual for how everything necessary for life must be done. At the smallest level, DNA is organized into a double helix as shown in the illustration above. The DNA helix is then repeatedly coiled to allow more of it to fit into a compact space. In humans, all the DNA is packaged into 46 separate molecules called "chromosomes." The chromosomes each contain thousands of genes, with each gene specifying how to make a particular protein necessary for cellular function. Scientists have long thought that the holy grail for understanding human life lies in knowing the entire sequence of human DNA. For this reason, the National Institutes of Health are funding the human genome project. The mission of the human genome project is to sequence all the DNA contained within a human cell. This is a project of enormous magnitude that will likely take many years to complete.
πThe Eardrum
The photograph above shows an eardrum (tympanic membrane) as seen through an otoscope. The dominant feature of the picture is the appearance of the middle ear bones (ossicles) that can be seen through the eardrum. Doctors are looking to see this normal anatomy when they examine a person's ear. The eardrum is a taut, thin membrane that vibrates in response to sound waves. Sound waves of different frequencies, like a bass drum or a violin, cause the eardrum to vibrate at different speeds. In order for the eardrum to vibrate freely, and thus work properly, the pressure needs to be the same on both sides of the eardrum. This explains why hearing decreases when the ears are clogged or when a person has a middle ear infection. Pressure equalization between the middle ear and the outside is achieved through the eustachian tube which connects the middle ear to the throat. It is unwise to ever place anything sharp into the ear that might damage the eardrum. However, the eardrum usually heals without problems if it is punctured. In fact, a common treatment for chronic middle ear infection in children is to place tubes through the eardrums that allow fluid to drain out from the middle ear. These tubes are called myringotomy tubes.
EThe Inner Ear
The inner ear consists of the cochlea and the semicircular canals. The cochlea serves to permit hearing while the semicircular canals are necessary for balance. The cochlea is a small, spiral shaped structure containing fluid and special hairs which serve as sound sensors. The photograph above shows a picture of some of these hair cells within the cochlea. Sound waves entering the ear set up a chain of vibrations, starting with the eardrum. The vibrations are then transferred via the middle ear bones (ossicles) to the cochlea. One of these bones (the stapes) moves up and down in the oval window causing fluid waves in the cochlea that are dependent on both the frequency of the sound, and its amplitude (volume). The response of the hair cells to these waves is dependent on their location within the cochlea. The cochlea is designed such that the hair cells right near the oval window move in response to high frequency sounds while those furthest from the oval window move in response to low frequency sounds. There is a very smooth gradient between the two extremes. The brain is thus able to tell what frequency a sound is by which of the hair cells in the cochlea are moving and sending out sound signals.
As noted above, the semicircular canals are necessary for balance. There are three of these canal that are positioned at right angles to one another. Like the cochlea, they contain fluid and specialized hair cells. They are different, however, because they contain small crystals that move freely in the fluid when the head moves. These crystals brush against the hair cells to indicate that the head has changed in position. If one spins around and around, the fluid and the crystals continue to move even after the head has stopped moving. This explains why a person becomes dizzy and may fall down from too much spinning.
üImaging with Sound
Ultrasound is an important diagnostic technique that has many uses in medicine. Ultrasound scanning is accomplished with a hand held device (transducer) that can emit very high frequency sound waves, and then "listen" for the return of the echoes. Different tissues vary greatly in their tendency to echo back the sound waves (echogenicity). These differences in echogenicity are used to create detailed images of the body. The sound waves emitted by the ultrasound machine penetrate through fluid very well, but they cannot penetrate through either bone or air. This is why the transducer must be placed right onto the patient's body with jelly used to exclude all of the air between the transducer and the skin. When ultrasound of the heart is done, it is called echocardiography.
Echocardiography is an extremely common test. It is used to study both the structure of the heart, and how well the heart is working. The main structural components of the heart that can be seen with echocardiography are: the four heart chambers, the four valves, and the walls which separate the right and left sides. In looking at the four heart chambers (two atria and two ventricles), the most important thing is their size. There is a definite normal range, above which the heart is said to be enlarged. An enlarged heart is typically a sign that it has begun to weaken and fail. The heart may be enlarged for many reasons. One of these reasons is a problem with one of the four valves. A valve can be either abnormally leaky (regurgitant), or abnormally narrowed (stenotic). Another possible cause of an enlarged heart is a hole in one of the walls that separate the right and left sides. There may be a hole between the two atria and/or a hole between the two ventricles. This "hole in the heart" condition is a very common birth defect, affecting about one in every 400 babies born. Typically the hole heals by itself, but sometimes surgery is required. The heart may also be enlarged because of an infection or a chemical which has damaged the heart muscle. Alcohol is one of the chemicals known to be toxic to the heart muscle if it is consumed in great excess.
Ectopic Pregnancy
Rarely, an embryo will accidently implant in a fallopian tube rather than in the uterus as it should. This is called an ectopic pregnancy. Unfortunately, the fallopian tube cannot expand and nourish the embryo as the uterus can, and there is no way for the embryo to develop to term. Usually, a woman with an ectopic pregnancy winds up in an emergency room complaining of severe lower abdominal pain and vaginal bleeding. A test is done first to determine if she is pregnant. If she is, then there is a reasonably high chance that she has an ectopic pregnancy. An ultrasound examination will usually be done next to help determine whether there is in fact an ectopic pregnancy. An ectopic pregnancy is an emergency that needs to be treated surgically. It is important to remove the developing embryo before the fallopian tube bursts. The primary risk factor for ectopic pregnancies is a history of fallopian tube infection which often scars the tubes. This makes it more likely that a fertilized ovum will fail to reach the uterus.
└EKG
As it beats, the heart generates small electrical currents. A recording of this electrical activity is called an "EKG" (electrocardiograph). The terms EKG and ECG mean the same thing. EKG comes from the German language while ECG comes from English. A standard EKG is obtained by placing 12 small electrodes on the patient's body in a specific pattern. The EKG machine is then turned on, and the recording is made in just a few moments. The test is entirely painless.
The picture above shows three heart beats taken from a normal EKG. Each of these beats can be divided into three main parts. The first part is the small P wave which represents the atrial contraction. The second part is the tall QRS spike which represents the ventricular contraction. The third part is the large T wave which represents the relaxation of the ventricles. By analyzing the exact pattern of the EKG, doctors can learn a great deal about how the heart is working.
rThe Zygote
As soon as fertilization takes place, the new cell is called a "zygote." Things immediately begin to happen within the zygote. First, the genetic material (DNA) is released from the head of the sperm. These 23 chromosomes are then able to join up with the 23 chromosomes of the ovum to form a full set of 46 chromosomes. The zygote thus contains all the genetic material for the new individual. Measuring only about four-thousandths of an inch (0.1 millimeter) in diameter, the zygote sets about the business of starting to divide while it continues its lazy journey down the fallopian tube toward the waiting uterus.
Twenty-One Day Embryo
After three weeks, the disk of cells becomes more elongated. The head of the embryo forms at one end while the lower part of the spine forms at the other. A group of cells along the embryo's developing back forms the notochord which goes on to form the spine itself. At this point in development, the embryo has a recognizable left and right side. The notochord next moves into the body of cells, away from the surface. The edges created curl around and fuse to form the neural tube itself. The neural tube goes on to form the brain and spinal cord. It is important to realize that these critical steps for forming the spine, spinal cord, and brain all take place scarcely after a women would realize she has missed her period. Prenatal care should really begin as soon as a couple even begins trying to conceive a baby. Sometimes, the neural tube fails to fuse properly. This may leave an opening in the brain or spinal cord called a neural tube defect. Recent studies have suggested that giving all women of child bearing age extra folic acid, a simple dietary supplement, may significantly reduce the frequency of neural tube defects. Of course, the folic acid needs to be given before pregnancy since the critical steps in neural tube formation occur so soon after fertilization.
GTwenty-Eight Day Embryo
During the fourth week after fertilization, most of the organs begin to be formed. The back grows more rapidly than the front, creating a C-shape to the embryo. Tissue buds develop that go on to form the lungs, the liver, the gallbladder, and the pancreas. The heart begins its development as a straight tube. Rudimentary ear and eye pits are seen. The neural tube also continues to develop as it extends more toward the head where the brain will develop. This period is called "organogenesis," since so many organs begin to be formed. It is at this point in development that the embryo is at greatest risk for developing birth defects from external toxins such as drugs or radiation. It is worth stressing that this critical period is quite early in pregnancy, soon after most women will have discovered that they are pregnant.
)Six-Week Embryo
By the sixth week after fertilization, the embryo begins to look recognizably human. The face begins to form along with the eyes and the ears. The limbs also start to develop rapidly and become jointed. The tail disappears. The embryo still has a long way to go, but it is well on its way.
bSeven-Day Embryo
On about the sixth day past fertilization, the sphere of cells implants into the uterine lining. At this point, the developing embryo begins to obtain its nourishment from the mother. The outer layer of cells go on to form the placenta at the point of attachment to the uterus. The embryonic cells, all initially in a ball, next begin to separate to form a flat disk with a fluid cavity on either side. The embryo at this stage is called a "blastula." The flat disk contains the cells that will ultimately go on to form all the baby's tissues. The amniotic sac develops around the embryo as it grows.
σEight-Cell Embryo
Nearly as soon as the zygote forms, it begins to divide again and again to form more cells. Initially, all of this cell division (mitosis) takes place without any change in the size of the developing embryo. The first cell division takes place about 24 hours after fertilization. The picture above shows the embryo at an eight-cell stage, about 48 hours or so after fertilization. The embryo is on its way to becoming a ball of cells, all exactly the same, called a "morula." Identical twins are formed when the cells of the morula split into more than one ball. This can sometimes occur during the frenzy to keep dividing. The separate and identical balls of cells can then each go on to form new and genetically identical people.
─Inside the Duodenum
The photograph above shows the inside of a normal duodenum as seen through an endoscope. An endoscope is a flexible tube with both a light and a camera lens at its end. Doctors often use the endoscope to examine the digestive tract when a patient develops vomiting or diarrhea that doesn't resolve as expected. Tiny surgical tools can also be manipulated through the endoscope, allowing treatment of a wide variety of digestive system disorders.
⌠Inside the Stomach
The picture above shows the inside of the stomach as seen through an endoscope. The endoscope is a flexible tube that allows doctors to look inside the body through a fiber optic lens at the tube's end. By using an endoscope, a doctor is able to look directly at the inside of the digestive tract to make a diagnosis, and possibly even to treat the problem. Some of the many problems that can readily be seen with an endoscope include tumors, ulcers, and dilated blood vessels (varices). The endoscope is controlled with hand-held dials that direct the tip of the endoscope so that it can be steered into the stomach and beyond. In the picture above, note the thick folds in the muscular stomach walls. This is the appearance of a normal stomach.
zHormones
Hormones are chemicals that are manufactured by glands within the body and then released into the bloodstream. From there, the hormones travel to all parts of the body where they influence a wide number of body processes. The glands which collectively make these hormones comprise the endocrine system. This system includes the adrenal glands, the gonads (testes or ovaries), the pancreas, the parathyroid glands, the thyroid gland, and the pituitary gland. In pregnant women, the placenta also functions as part of the endocrine system by making hormones that are released into the bloodstream. Hormones are also made by other organs including the kidneys and the heart, though these organs are not commonly thought of as part of the endocrine system. The process of releasing hormones into the bloodstream is called "exocytosis." This process is shown in the illustration above.
HFetal Monitor
The birth process is quite stressful for both the mother and baby. Although most births are uncomplicated, there is always the potential for something to go wrong. For this reason, it is commonplace to use a fetal monitor to assess the status of the baby throughout the labor and delivery. The fetal monitor typically uses a small probe which is attached to the baby's head through the cervix. With this probe, it is possible to determine continuously the baby's heart rate. A belt is usually placed on the mother as well to monitor the rate and strength of her contractions.
°Female Reproductive System
The female reproductive system consists of the ovaries, the fallopian tubes, the uterus, and the vagina. These structures are all shown in the illustration above, with the ovaries and uterus highlighted in orange. The eggs are all contained within the ovaries. Each month, there is a cycle of hormones which causes one of the woman's eggs to mature and burst out from the ovary. The egg cell, or ovum, is then picked up by one of the fallopian tubes which gently brushes the ovum down toward the uterus. The uterus has already readied itself for the ovum by increasing the thickness of its lining. If the ovum is fertilized by a sperm, then the ovum will implant in the uterine lining and develop into a new baby. If it is not fertilized, it will wither away, and the uterine lining will be discarded in a process known as menstruation. The whole process repeats itself each month throughout a woman's reproductive years. Interestingly, a women is born with all the egg cells that she will ever have. During childhood, the egg cells lie dormant, awaiting puberty when they will begin to mature and be released. Women have many thousands of eggs, but only one, or at most a few, mature each month. Women thus have many more egg cells than can ever be released.
Ten-Week Fetus
The developing child is referred to as a "fetus" rather than an "embryo" after the eighth week. The photograph above shows a fetus at approximately the tenth week of development. At this point, the fetus is about two inches (five centimeters) in length. Blood cells are being produced by the liver and spleen, and the now-completed fetal heart is already pumping these red blood cells around the body. At this point, all the organs have formed. Further development mostly involves maturation of these rudimentary organs.
ìFour-Month Fetus
This remarkable photograph shows a fetus after four months of development. The face is quite well developed as are the hands. Sometimes, fetuses of this age can even be observed sucking their thumb. This photograph was obtained by using a special fiber optic camera that was placed inside the uterus. Even the detail in an ultrasound picture pales in comparison to that seen in this image.
"Eight-Month Fetus
By eight months after conception, fetal development is nearly complete. The baby can be expected to do satisfactorily if it is born at this stage, though there could be minor complications. Among the last things to develop to full maturity are the lungs. The illustration above shows the fetus with its head down, firmly seated against the cervix. This is the optimal position for the fetus to be in for a vaginal delivery. Also evident in the illustration is the placenta, which serves as the connection between the fetus and the mother.
╥The Flu Virus
There are three main types of influenza viruses, named type A, B, and C. The schematic illustration at left shows a single influenza virus. Among the most notable features are the little spikes (shown in white) that stick out from the viral surface. The exact nature of the spikes (glycoproteins) determines the type of the influenza virus. Immunity to influenza occurs when the immune system makes antibodies that bind to these glycoprotein surface spikes. Unfortunately, the type A and, to a lesser extent, type B influenza viruses are unstable, with new versions appearing every year. When a new version appears, the antibodies still circulating in the body from the last bout of influenza will be less effective at eliminating the virus, and the person may get ill once again. Occasionally, an influenza virus will appear that is so radically new that virtually no one is immune to it. When this occurs, the result is a worldwide flu outbreak called a "pandemic."
╤Upper GI Series
The upper GI series is a common method for looking at the digestive tract. The digestive tract is also called the gastrointestinal (GI) tract, hence the name "upper GI series." This technique has been used for many years. It has the advantages of being cheaper and less invasive than endoscopy. An upper GI series involves the patient drinking a small amount of a barium solution while x-rays of the esophagus, stomach, and small intestine are taken from many angles. The barium solution outlines the inside of the digestive system and enables excellent diagnostic pictures to be taken. For most patients, the worst part of this test is the taste of the barium, which is usually described as seeming like chalk.
.Gallstones
A common medical problem is the formation of gallstones within the gallbladder. These stones are of three main types: cholesterol stones, pigment stones, and mixed stones. The picture above shows examples of the different stone types. The majority of stones are of either the cholesterol type or the mixed type. Four times as many women as men are affected by gallstones. Most gallstones are silent and cause no problems. Sometimes, however, a stone can become lodged in the neck of the gallbladder or in the cystic duct, leading to great pain and infection of the gallbladder. Removal of the gallbladder is the most common treatment for this problem. Removing the gallbladder does not seem to have any harmful effect on digestion or any other process. In recent years, a method for removing the gallbladder without major surgery has come into widespread favor. This procedure is called "laparoscopic cholecystectomy." Patients undergoing this procedure are generally released from the hospital after only one day, and they can return to work within a week.
&Keeping the Beat
The heart beat is usually divided into two main phases called "diastole" and "systole." During the first phase (diastole), the heart relaxes and fills with blood. During the second phase (systole), the heart contracts and pumps out the blood. The heart typically spends about 2/3 of its time in diastole and 1/3 of its time in systole. Keeping this activity well timed is the job of the heart's conduction system.
The signal to begin a contraction starts in a small region at the top of the right atrium called the "sinoatrial (SA) node." From this point, the contraction spreads over the two atria like a wave. The atrial contraction pumps the blood down into the ventricles. Next, the signal to contract reaches a small region of the heart called the "atrioventricular (AV) node." As its name implies, the AV node sits right between the atria and the ventricles. The AV node is smart, and it delays the signal just long enough to allow the atria to finish contracting. From here, the signal to contract travels down special fibers that connect to the bottom of the heart. This causes the ventricles to contract from the bottom to the top, and ensures that the blood is pumped up and out, into the lungs and the body. At the end of the cycle, the ventricles relax and the whole process begins again.
▀Coronary Arteries
Although the heart is constantly pumping blood, it does not actually get any oxygen from the blood which travels through its chambers. Instead, the heart receives all of its oxygen from the arteries which encircle it. These blood vessels are known as the "coronary arteries." The word "coronary" comes from the Latin word "corona," which means crown. There is a right and a left main coronary artery. These all-important arteries exit from the aorta just above its attachment to the heart. The left main coronary artery is actually quite short. Soon after exiting from the aorta, it divides into two large branches called the "circumflex" and the "left anterior descending" arteries. Under normal circumstances, the coronary arteries have significant reserve capacity, and they can easily meet the oxygen demands of the heart muscle. Problems with supplying the heart muscle with oxygen arise only when the coronary arteries become significantly narrowed due to atherosclerosis.
┴Heart Attack
People with coronary artery disease are at high risk for having a heart attack. A heart attack occurs when the blood supply to a part of the heart is suddenly cut off, and the affected heart muscle dies. The usual cause of a heart attack is the formation of a blood clot at the site of an atherosclerotic plaque. The clot completely blocks the artery, cutting off blood flow beyond it. The medical term for a heart attack is myocardial infarction.
Heart attacks are the number one cause of death in western societies. The risk factors for having a heart attack are well known. These risk factors include a diet high in fat and cholesterol, smoking, obesity, physical inactivity, high blood pressure, diabetes, and a family history of heart attacks. Fortunately, most of these risk factors are related to lifestyle. It is thus possible for a person to lower their risk of a heart attack if they choose to. Of note, the incidence of heart attacks is four times lower in Japan than it is United States. This is because the major risk factors are much less common in that country.
The diagnosis of a heart attack is based mostly on the patient's symptoms. Typically a patient having a heart attack experiences severe chest pain, sweating, nausea, and anxiety. The diagnosis is confirmed by an EKG along with blood tests. If a patient arrives at the hospital soon after their symptoms began, they will generally be treated with a medicine (thrombolytic) that works by dissolving blood clots. This treatment is often successful at reopening blocked arteries, and limiting the damage done to the heart. The severity of a heart attack is determined by how much of the heart dies. If too large a part of the heart is affected, the remaining heart muscle is unable to continue pumping the blood. Approximately one third of heart attacks are fatal. Advances in medical care over the past 30 years have greatly improved the outlook for patients that survive a heart attack.
ⁿOpen Heart Surgery
Open heart surgery first became possible in the mid-1950's when the heart-lung machine was introduced. Once connected, this machine serves to oxygenate and pump blood to the brain and other tissues throughout the body. This enables the surgeons to stop the heart, open it up, and make needed repairs, all the while taking as much time as is needed.
The most common open heart operation in the Western world is coronary artery bypass grafting. Another common heart operation is valve replacement. The most aggressive open heart operation is heart transplantation. The first successful heart transplant program began at Stanford University in 1969. One of the biggest problems with organ transplantation is rejection of the transplant by the patient's immune system. In the last ten years, however, there has been significant advancement in the medicines that are used to prevent rejection. Approximately 85% of patients receiving a heart transplant can now expect to live for at least a year after the surgery.
₧Compact Bone
Bones are formed of a thin outer surface layer (periosteum) containing blood vessels and nerves, an outer shell made of dense compact bone, and a core composed of spongy bone. The dense outer shell is made of orderly columns of bone cells that are mineralized with calcium phosphate to make them resilient and strong. These bone columns are called Haversian canals. The photograph above shows a number of Haversian canals in cross section.
Bone growth and shape is the result of a delicate balance between calcium deposit and resorption. Osteoblasts are bone cells that work to deposit new calcium phosphate taken from the blood, while osteoclasts work to resorb calcium phosphate and return it to the blood. This balance is controlled by many different hormones (growth hormone, sex hormones, adrenal hormones, thyroid hormone, and parathyroid hormone). It is very important that the amount of calcium in the blood be strictly regulated so that muscles and nerves in the body function properly. The growth and shape of bones is also influenced by the mechanical stresses placed on them. This ensures that the bones that support the weight of the body are very strong.
╤The Auditory Pathway
Hearing begins with the pinna channeling sound waves into the ear canal as shown in the illustration above. These sound waves cause the eardrum to vibrate. The middle ear contains three delicate bones (ossicles) which are attached to the eardrum on one side and the cochlea on the other. When the eardrum vibrates, the ossicles move with it and transfer the vibrations to the fluid within the cochlea. The cochlea is a spiral, seashell-shaped structure containing fluid and many specialized hairs that move in response to fluid waves. Movement of the hair cells stimulates nerve fibers to send a signal to the brain. The louder the sound is that enters the ear, the more the eardrum moves, and the stronger the waves are that are created in the fluid within the cochlea. In turn, the hair cells in the cochlea move more, and a stronger signal is sent to the brain along the eighth cranial nerve. Ultimately, the brain will interpret the strong signal as a loud sound.
Hemoglobin
Red blood cells are completely filled with hemoglobin, a special molecule designed to carry around oxygen and carbon dioxide. Amazingly, there are about 350 million hemoglobin molecules in each and every red blood cell. The hemoglobin molecule consists of four basic units (globin chains), as shown in the picture above. The four chains always consist of two matching pairs. In the adult human, there are two identical alpha chains, and two identical beta chains. Each of the four chains has a single iron atom in its center. The four iron atoms enable the hemoglobin molecule to bind with four oxygen molecules. Oxyhemoglobin is formed when oxygen molecules combine with hemoglobin. Oxyhemoglobin is bright red, and it gives blood its usual color. When the oxygen molecules are released into the tissues, however, hemoglobin turns greenish. This explains why venous, deoxygenated blood appears darker than arterial, oxygenated blood. This is easily observed in the veins that are just beneath the skin surface.
HLiver Cell
The illustration above shows a single liver cell, commonly referred to as a hepatocyte. Its general structure is the same as other cells. It is surrounded by a membrane that keeps the cell intact, while excluding undesirable molecules from freely entering the cell. Cell membranes have specific channels in them that are used to regulate the passage of molecules into and out of the cell. Inside the cell there are numerous cellular "organs" called organelles. These structures perform specific functions that are needed by the cell, such as the synthesis of new cell components. One of the most important organelles is the mitochondria which are shown in purple above. The mitochondria are responsible for producing energy for the cell. At the middle of the cell is the nucleus. The nucleus contains the DNA. The DNA serves as the instruction manual for how to carry out all the cellular functions. Interestingly, all the different cells in the body have the same DNA. Somehow, the different types of cells all know enough to read the pages of the manual that are specific to them.
ΦArtificial Hip
The movable joints of the body have fibrous capsules that are lined with a membrane (synovium) that secretes a thick lubricating fluid. The moveable joints also have cartilage at the ends of the bones which acts as a cushion between the bones. These joints are referred to as synovial joints. Osteoarthritis is a joint disease caused either by damage to the cartilage within the synovial joints, or by the formation of bony spurs. Osteoarthritis is the same thing as degenerative arthritis. Nearly all people over the age of 65 have osteoarthritis to a greater or lesser extent so it can reasonably be thought of as part of the aging process. In some people, however, osteoarthritis is quite severe, causing great pain and disability. The hips, knees, and spine are particularly prone to osteoarthritis as is the joint at the base of the thumb.
When severe osteoarthritis causes joint destruction, it is often possible to offer joint replacement as a method of treatment. Hip replacement is the most common of these operations. In this operation, the top of the femur is removed along with the normal hip socket. A metal shaft with a ball at its top is placed into the remaining part of the femur. A cup made of metal or plastic is placed into the pelvis. This operation is usually very successful, often restoring patients to a normal level of activity. Other joints including the knee and shoulder are sometimes replaced, but the results are generally not as reliable as with hip replacements.
▄AIDS Virus
Every time period appears to have had its own scourges, and our time is no different. Today the health community and the public are confronted with the AIDS problem. AIDS stands for acquired immuno-deficiency syndrome. AIDS is a clinical condition in which the body repeatedly succumbs to opportunistic infections because of a weakened immune system. AIDS is caused by the human immunodeficiency virus (HIV). Thus far, it appears that all individuals who contract HIV will eventually develop AIDS, a uniformly fatal disease. There are medications that slow the course of the disease, but no definite cure is on the horizon. One would think that the answer to the problem lies in an effective vaccine, but scientists have thus far been unable to make such a vaccine. HIV is an unusual virus in that it attacks the very cells in the immune system whose normal role would be to kill the virus. No such virus had ever previously been isolated. Fortunately, the routes of HIV transmission are well understood, and show no signs of changing. At present, it is only possible to contract HIV by exposure to either blood or genital tract secretions from an infected person. Unprotected sex with infected partners and needle sharing remain the most common routes of transmission by far. Exposure to HIV through blood transfusions was largely eliminated in the mid 1980's when screening tests for HIV became available. The picture above shows a virus budding out from an HIV infected lymphocyte.
UInsulin
Insulin is an important hormone that is made by the pancreas. After a meal is eaten, insulin is released. The insulin serves as a messenger to all the cells of the body that they should take up glucose (sugar) from the blood and store it. Diabetes is a disease generally caused by an underproduction of insulin. Without this signal, the cells fail to take up the glucose, and blood sugar levels can rise to very high levels. When the blood sugar level reaches a high enough point, glucose begins to spill into the urine. This is why doctors initially check the urine to test for diabetes.
ΩThe Small Intestine
The illustration above depicts a short segment of small intestine. The small intestine is a long tube (about 21 feet, or 6.5 meters) whose purpose is to absorb food. The inner layer of the small intestine (mucosa) is very well suited for this job. It is organized into innumerable little, finger-like projections called "villi." The mucosal cells which line the villi are in turn covered with even smaller finger-like projections called "microvilli." The villi and microvilli greatly increase the surface area with which to absorb food. The middle layer of the small intestinal wall contains two layers of smooth muscle. These smooth muscle layers contract in a rhythmic manner (peristalsis) to keep food moving down the digestive tract.
Irritable Bowel
Irritable bowel syndrome is a condition in which people experience intermittent abdominal pain and irregular bowel habits without any other demonstrable evidence of disease. People with irritable bowel syndrome have no other symptoms, and they do not become either malnourished or lose weight. The cause of this syndrome is not well understood, but is assumed to be related to some disturbance of the smooth muscle within the walls of the large intestine. Surprisingly, it is the most common intestinal disorder, accounting for more than half of all the patients seen by doctors who specialize in digestive system problems (gastroenterologists). Prior to making the diagnosis of irritable bowel syndrome, it is still necessary to run tests to exclude other more treatable illnesses.
±Edward Jenner
The principle of vaccination is one of the landmark discoveries in the history of medicine. This triumph is credited to Edward Jenner. In his time, the great scourge was smallpox, a highly infectious and lethal viral infection. Its impact on the population at that time dwarfs the impact that AIDS, the worst scourge of our time, is having today. Edward Jenner made the astute observation that the milkmaids of that day rarely ever developed smallpox. He reasoned that something about their tendency to contract a similar illness called cowpox might be involved. He hypothesized that these milkmaids were resistant to smallpox because they had already contracted a similar illness. In 1796, Edward Jenner tested this hypothesis by inoculating his eight year old son with material obtained from a cowpox lesion. Six weeks later, his son proved resistant when he was challenged with material from a smallpox lesion. The principle of immunization was thus established. This is an epic story indeed when you realize that Edward Jenner's young son would likely have died if Edward was wrong about his hypothesis. As an interesting footnote, the elimination of the smallpox virus ranks as one of the most significant successes of the World Health Organization (WHO). In 1967 the WHO mounted a campaign to eliminate small pox from the earth which culminated in 1977 when the last known case was recorded in Somalia. Only research strains of the smallpox virus remain, located in a few laboratories in the world.
Cleaning the Blood
The kidneys receive their blood supply directly from the aorta through the renal arteries. These arteries branch again and again within the kidneys to form small capillary tufts called "glomeruli." Each kidney contains about one million glomeruli which together serve as the filter for cleaning the blood. Blood cells and big molecules are kept within the glomeruli, but water and small molecules all pass through their walls. In fact, about 140 liters of fluid pass out of the glomeruli each day. All this fluid passes into the renal tubules where 99% of it is reabsorbed back into the blood. At the end of the tubules, however, the waste products, excess salt, and some of the water remain unabsorbed. These things form the urine which drains down the ureters and into the bladder.
Kidney Stone
There are a number of different types of kidney stones. The most common type, as shown in the picture above, is made of calcium salts. These stones are extremely hard, and they often have sharp edges. There is usually no definite cause for the formation of these stones, although diet and fluid intake certainly play a role. Less commonly, kidney stones form because of a kidney infection or some definite, treatable metabolic disorder. It is easy to see from the picture above why passing kidney stones causes such incredible pain.
VShock Waves
Sometimes, kidney stones form which are simply too large to pass. In the past, doctors used to perform surgery to remove the stones. In recent years, however, doctors have begun using a machine called a "lithotriptor" to treat large kidney stones. This treatment is non-invasive and relatively simple. As shown in the picture above, the patient sits in a bath of warm water during the procedure. The lithotriptor then emits high energy sound waves which are focused on the kidney stones. The sound waves pulverize the stones into small fragments that can then be passed through the urine.
&The Chemical Factory
The liver is a remarkably complex organ which serves as the chemical factory for the body. There is a very wide range of functions that are performed by the liver. One of these functions is to produce important proteins for the blood. Some of these proteins play roles in the immune system (complement factors), some in the blood clotting pathway (coagulation factors), and some in the regulation of intravascular blood volume (albumin). Another function of the liver is to help regulate blood sugar levels by storing glycogen when glucose is plentiful, and releasing it when it is needed. The liver also regulates the levels of many key molecules, such as amino acids.
Perhaps the most important role of the liver is to detoxify and remove many poisonous substances from the blood. The liver does this by absorbing the toxins from the blood, altering their structure to make them water-soluble, and excreting them into the bile. The bile is then emptied into the small intestine, and the now harmless toxins are eventually eliminated with the feces.
╡Receptors
Neurotransmitters are the messengers for nerve communication across synapses. However, there are many different types of chemicals that serve as neurotransmitters. How do the receiving cells distinguish all these signals? They do this by having very specific receptors. Each receptor is like a lock that can only be activated by a particular key, as in the correct neurotransmitter. The illustration above shows a neurotransmitter molecule bound within a receptor. Most drugs and toxins that affect the nervous system work by modifying the interaction of neurotransmitters and their receptors.
One of the most important neurotransmitters is acetylcholine (ACh) which is released by the neurons that stimulate skeletal muscles. Receptors on the muscle fibers recognize ACh as the signal to contract. Many animals, such as venomous snakes and puffer fishes, produce toxins that cause paralysis by blocking the ACh receptors. There is also a disease called Myasthenia Gravis that involves the ACh receptors. Patients with myasthenia gravis produce antibodies that bind to the ACh receptors and prevent them from receiving the normal signals to contract. Myasthenia patients thus suffer from profound weakness since their muscles don't contract when they are supposed to. Treatment involves administration of a medicine which causes the nerve terminals to release more acetylcholine than normal. Myasthenia Gravis is an example of an autoimmune disease. Autoimmune diseases result from a disorder of the immune system in which antibodies are made that react with normal parts of the body. Under normal circumstances, antibodies are only made to react with foreign molecules that are invading the body.
ELung Cancer
In the U.S., lung cancer has been the leading cause of cancer deaths in men for many years, and only recently has it achieved this same dubious status in women. Cigarette smoking is the main cause of lung cancer. The risk for developing lung cancer is directly related to the number of cigarettes smoked per day, and the length of time that a person has smoked. Doctors commonly use the term pack years, which is the number of cigarette packs smoked per day times the number of years that the person has smoked. The steady rise in the number of women developing lung cancer can be seen to correlate with an equal rise in the use of tobacco by women in the 20th century.
The photograph above shows a segment of the lung. Note how the cancer cells, shown in green, appear to be invading through the normal healthy respiratory lining, shown in yellow. This is a general property of malignant cancer cells. They tend to be disorganized, relatively non-functional cells, that lose regard for traditional boundaries and multiply out of control. They also have the ability to spread to distant sites, a process called metastasis. Lung cancer usually does not cause symptoms until late in the course of the disease. The first symptom is most commonly a worsening cough. Some people, however, are fortunate to have a lung cancer noted on a routine chest x-ray, early in the course of the disease. In these cases, the prognosis can be very good for long term cure. Available treatments include surgery to remove cancerous tissue, radiation therapy to kill cancer cells, and anti-cancer medicines.
"The Respiratory Tree
The structure of the lungs can be likened to a branching tree. Starting with the trachea (windpipe), the respiratory tree branches initially to form two main bronchi (airways) that enter the right and left lungs. The main bronchi then branch again and again, first forming smaller bronchi and then even smaller bronchioles. At the end of the smallest bronchioles, there are tiny, grape-like air sacs called "alveoli." It is in the alveoli that oxygen comes into contact with the red blood cells that will carry it to all parts of the body.
ºBack Pain
Neck and back pain are very common ailments. Most commonly, this pain results from strain of the muscles which support the spine. This type of pain is best treated with rest and heating pads. Occasionally, however, there is damage to the spine itself. Arthritis is the most frequent cause of spine problems. One of the ways arthritis can cause pain is by narrowing the small openings through which the spinal nerves exit from the spine. This causes pain by directly putting pressure on the spinal nerves.
Another cause of back pain is damage to one of the intervertebral disks. A ruptured disk occurs when severe pressure forces the jellylike core of the disk out through the tough disk capsule. A slipped disk occurs when severe forces move the disk out of its normal location. Disk injuries are serious, and they typically require surgical treatment to fix.
Sciatica is a general term for back pain that extends down into the buttock and leg, along the course of the sciatic nerve. Sciatica usually results from pressure on the lumbar and sacral nerve roots that exit the spine to form the sciatic nerve. Arthritis and disk damage are just two of many causes of sciatica.
òLymph Node
The illustration above shows a cross-section of a lymph node. Each node has a capsule and an internal mass of lymphoid tissue. Several lymph vessels carry lymphatic fluid into the node, with a single large vessel carrying the lymphatic fluid back out. The lymphoid tissue is home to many white blood cells of the lymphocyte type. These are the white blood cells that generate antibodies. Lymph nodes also include macrophages (phagocytes) that engulf foreign particles and eliminate them. Lymph nodes are found in groups or chains throughout the body. They serve largely as a barrier to the spread of infection. Lymph nodes are also commonly involved in cancer. This occurs because the cancer cells that metastasize (travel to distant locations) are filtered out by the lymph nodes in a fashion similar to infectious organisms. Enlargement of lymph nodes is often the first sign that a cancer has spread.
Mammography
Breast cancer is a common ailment in the U.S., affecting as many as one in every 11 women during their lifetime. Like most cancers, the prognosis is greatly improved by early detection. The easiest method for enhancing early detection is breast self examination. All women are encouraged to do a self breast examination each month. It is best done at the same point in the menstrual cycle each time. The purpose of the self exam is to note any new or unusual lumps, or a change in the appearance of the breast. Unusual changes should be reported to one's doctor for further evaluation. Another method for increasing early detection of breast cancer is mammography. The picture above shows a women who is having a mammogram done. Several studies have shown that breast cancer deaths can be decreased by routine screening of otherwise healthy women using mammography. Specific recommendations tend to change, but mammography remains a prudent screening test for individuals wishing to increase their chance of early cancer detection.
Melanoma
Malignant melanoma is the most serious form of skin cancer. It appears on the skin initially as a small, but ugly looking dark bump. It will usually have ragged edges and multiple colors within it. It may even start to bleed spontaneously. Melanoma is an aggressive cancer that spreads early in its course. The illustration above shows several melanoma cancer cells entering a blood vessel on their way to spreading to some distant part of the body. This process is called metastasis. Cure for melanoma depends on surgical resection of the disease. If it has spread at the time of surgery, then the prognosis is very poor as melanoma cells are quite resistant to the usual forms of chemotherapy and radiation therapy. The likelihood of distant spread is directly related to the depth that the cancer has penetrated into the skin. This depth is a number in millimeters that is reported when either a biopsy or resection is done. The incidence of melanoma continues to rise in the US. This is attributable to our culture which encourages people to tan themselves. Fair skinned people are at particularly high risk for developing melanoma. It is important that all suspicious skin lesions be promptly reported to a dermatologist or other doctor for further evaluation.
hDigestion
The photomicrograph above shows a closeup of a mucosal cell which lines the inside of the small intestine. Each of the tiny, finger-like projections on this cell's surface are called "microvilli." If we were further away, we could see that the inner lining of the small intestine is itself organized into many small, finger-like projections called "villi." The villi and microvilli together create a surface area within the small intestine that is as large as a tennis court. The main purpose of this lining is to promote the effective absorption of food. This is a job it is quite well designed to perform.
Migraine Headache
Of the many ailments of the brain, the most common is headache. Interestingly, the brain itself contains no sensory fibers, and it cannot actually cause pain. Instead, headache pain comes from the meninges which cover the brain, and the scalp, with its muscles and blood vessels. Headaches are usually a response to external stimuli. Only rarely are they indicative of a serious underlying disorder.
The most severe headache type is migraine. Migraine headaches are usually accompanied by nausea, vomiting, and disturbances of vision. The disturbances of vision precede the pain and are called an aura. Other neurologic symptoms such as weakness can also occur. Patients experiencing a migraine headache usually choose to lie very still in a dark room while waiting for the pain to subside. Migraine headaches are relatively common, affecting three times as many women as men. Migraine sufferers typically report a definite pattern to their headaches, and they can report what stimuli bring them on. Most migraine sufferers experience their first attack before the age of 20. There is no single cause of migraines, but the tendency to get migraines does tend to run in families. A new medication, sumatriptan, shows promise for the relief and prevention of migraine attacks for many patients.
Æ Malaria
Malaria is a parasitic disease spread by the bites of Anopheles mosquitos like the one shown in the illustration above. The parasites responsible for malaria are single-celled organisms called plasmodia. The plasmodia spend part of their life cycle in humans and the remaining part in the Anopheles mosquitos. The plasmodia reproduce in human red blood cells. When the plasmodia are mature, the red blood cells burst and release more plasmodia which then go on to infect even more red blood cells. The bursting of the red blood cells tends to occur in cyclic fashion, every two or three days depending on the type of malarial parasite; there are four different types. When the red blood cells burst, it produces severe chills (rigors) followed by a very high fever. These are the characteristic symptoms of malaria. Malaria is a serious illness that is oftentimes fatal because of all the burst red blood cells which can cause failure of the kidneys and liver. The broken red blood cells can even block blood vessels to vital organs such as the brain, leading to convulsions and coma.
Malaria is present in much of the tropics throughout the world. In Africa alone, malaria kills more than a million infants and children every year. Those that survive develop some measure of immunity. The World Health Organization has embarked on a massive effort to control malaria with only limited success. The mosquitos have developed resistance to the insecticides, and the plasmodia that cause malaria are developing resistance to the drugs normally used to treat the disease. It is very unlikely that anyone would contract malaria in the United States, but about 1,000 US citizens contract malaria each year as a result of travel abroad. It is absolutely necessary for people traveling to endemic malaria regions to take medications that inhibit the malaria parasites from growing, and to take precautions to avoid being bitten by mosquitos.
Of note, sickle cell disease has an important relationship to malaria that is easily explained. Normal people have two copies of the gene (DNA segment) that specifies how to make a beta hemoglobin chain. Sickle cell disease occurs when both of these copies are replaced with abnormal sickle cell versions. Recall that red blood cells are entirely filled with hemoglobin molecules. People with two normal beta hemoglobin genes make normal hemoglobin, and are very susceptible to contracting malaria. People with one normal gene and one of the sickle cell genes make a hybrid form of hemoglobin that renders the red blood cells more resistant to malaria. People with two copies of the sickle gene produce sickle cell hemoglobin which causes sickle cell disease. Over the thousands of years that people have been exposed to malaria, there has been strong selective pressure to keep the sickle cell gene around, despite the fact that it causes a serious disease when someone winds up with two copies of it.
ß3-D Body Adventure
Click directly on the body to begin exploring. To move the body to a new position, click on the rotate body icon. Use the arrow keys or move the mouse to rotate the body. Click the mouse, or hit any key to get a cursor.
bBrain Imaging
Along with CT scanning, magnetic resonance imaging (MRI) has come into widespread use in recent years for imaging the brain and spinal cord. The photograph above shows a patient lying on the gantry of an MRI scanner. The basic principles of physics that make MRI possible have been known since the 1940's, but it wasn't until the 1980's that doctors were able to use this knowledge to make useful images of the body. In most situations, MRI provides better contrast between normal and abnormal parts of the brain than CT scanning does. This makes the diagnosis of disease easier. On the other hand, MRI machines are much more expensive to purchase and operate than CT scanners, and an MRI exam takes much longer to perform, making the test unsuitable for very ill patients. Also, patients hooked up to pumps or other machines with metallic parts cannot be brought into the vicinity of the MRI because of its strong magnetic field. Imagine the sight of all these metal objects flying into the magnet. For the foreseeable future, CT and MRI will remain complementary methods of studying the brain and spinal cord.
Γ Pictures from Magnets
Magnetic resonance imaging (MRI) is a valuable diagnostic technique that has been in general clinical use since the early 1980's. MRI provides doctors with very high quality images of the body without using x-rays. MRI works by detecting weak radio signals that are emitted from the hydrogen nuclei (protons) within the body. This works well because each water molecule (H2O) contains two hydrogen nuclei, and nearly 99% of the molecules in the body are water molecules. Because water molecules are small, however, the body is only about 60% water by weight.
During the MRI exam, the patient lies in a large, powerful magnet. All the hydrogen nuclei (protons) in the body promptly align with this magnetic field. Normally, these protons are all tumbling about randomly. The MRI machine is able to align them only because its magnetic field is more than 10,000 times stronger than the usual magnetic field on the earth. After getting all the protons into alignment, the MRI machine emits a strong radio frequency pulse which briefly knocks all the protons back out of alignment. As the protons come into alignment once again, they emit a weak radio signal of their own which is detected by the machine. The strength of this signal depends both on the concentration of the protons, and what else is around them. For practical purposes, the concentration of protons is the same as the concentration of water. For instance, bones have very little water, so they have almost no signal and appear black with MRI. In contrast, fat has lots of water, and it emits a bright signal which appears white with MRI. The MRI machine is able to distinguish the signals coming from each tiny little piece of tissue and then recombine them to form an exquisitely detailed image.
MRI has found widespread use in many areas of medicine. It is a particularly valuable method for imaging the brain, spinal cord, spine, shoulder, and knee. Its value in imaging other parts of the body continues to grow as radiologists learn more about how to perform MRI exams. There are no known risks or side effects associated with MRI. There is no radiation, and the test can be performed repeatedly without adverse effect. However, MRI should not be done on some people with metal implants within the body, and on people with pacemakers or other electrical devices that are sensitive to high magnetic fields. Also, the tunnel like hole in the magnet where the patient lies causes great psychological stress for people with claustrophobia.
┘ Nerve Fibers
A nerve is a bundle of nerve fibers that all travel together to the same location. Each of the nerve fibers (axons) comes from a separate neuron. The photograph above shows a bundle of several axons. There are 31 pairs of spinal nerves which exit from the spinal cord. Several of these spinal nerves join together to form the sciatic nerve which is the largest nerve in the body. The sciatic nerve supplies the leg with both motor (movement) and sensory nerve fibers.
There is a very specific pattern to the way sensory neurons travel from the surface of the skin to the spinal cord. This is called the dermatome pattern. The word dermatome is related to the word dermis, meaning skin. The dermatomes are a series of rings that can be drawn on a picture of the body. Each ring is connected to the spinal cord at a specific level. When a person loses sensation over a particular part of their body, it is possible to look at the dermatome pattern to determine which level of the spinal cord is involved.
The sensory fibers which serve the internal organs also enter the spinal cord at specific levels. Interestingly, pain coming from these fibers is not generally perceived as coming from the organs themselves. Rather, the pain is perceived as coming from the area of the skin whose pain fibers enter the spinal cord at the same level as those of the painful organ. As a rule, the internal organ pain fibers do not enter the spinal cord at the same level as the skin which lies directly over the organ. An example of this is heart pain, which is often felt as pain in the neck or left shoulder. This is a very general concept known as referred pain. Doctors can often interpret the descriptions of pain given by patients to determine where the real problem is within the body.
Surprisingly, people are born with all the neurons they will ever have. When the cell body of a neuron dies, it is gone, and it will never be replaced. Peripheral nerve injuries typically affect only the axons, however, and not the cell bodies. When a peripheral nerve is cut, the distal segment of each injured axon degenerates, and the proximal segment begins growing to replace the lost distal segment. This is possible because the proximal axonal segments are still attached to the cell bodies. If the severed ends of the nerve are close together, the channels left by the old axons help guide the new axons to the right location. This regeneration of axons is a very slow process. Axons only grow at the rate of about 1 inch (2.5 cm) per month. Unfortunately, this healing process is rarely perfect. People are often troubled to find that their bodies do not do what they expect them to do after the axons have grown back. The ability of neurons to regenerate their axons is strictly limited to the peripheral nervous system. Neurons in the spinal cord and brain (CNS) are in some way different, and they cannot repair themselves after injury. This is why spinal cord injuries typically result in permanent disability.
3Nerve Cell
The basic function of the nervous system is to transmit messages from one place to another. The nerve cells which do this job are called neurons. Neurons can vary widely in their shape, but they all have several basic things in common. Like all cells, neurons have a cell body. These cell bodies have many short branches coming off of them called dendrites. Dendrites allow communication with nearby neurons. Each neuron also has a single long branch called an axon. Axons permit messages to be carried to distant neurons in other parts of the body.
There are three basic types of neurons. These are sensory neurons, motoneurons, and interneurons. Sensory neurons carry signals from their sense receptors in the periphery back to the central nervous system (CNS). Motoneurons carry signals from the CNS to the muscles and glands within the body. Interneurons do the communicating within the CNS itself. For each sensory neuron, there are about 10 motoneurons and 100 interneurons in the body. Apparently, many more neurons are required to decide what to do in response to incoming signals than are required to get those signals.
Neurons actually function by conducting electrical signals down the length of their axons. The axons are wrapped with myelin cells which serve just like the insulating material that surrounds regular copper wires. These electrical signals travel down neurons at speeds over a hundred miles per hour. This seems quite fast unless you compare it to real copper wires which conduct signals at the speed of light (186,000 miles per second).
sEndorphins
Opium and its derivative morphine have been used to relieve pain for more than 100 years. It wasn't until 1973, however, that scientists discovered the actual receptors in the brain that morphine binds to. This discovery raised the question of why all people would happen to have receptors for a chemical produced from poppy flowers. The question was soon answered by the discovery of endorphins, the natural molecules produced by the body that react with the morphine receptors. The name endorphin comes from the phrase, endogenous (self) morphine. Since the initial discovery of endorphins, several related molecules have also been discovered that are called enkephalins. The morphine receptors are now more commonly referred to as opioid receptors. The brain illustration above depicts regions known to contain opioid receptors in yellow and pink.
Interestingly, it is widely thought that acupuncture works by stimulating the production of endorphins. The euphoria some people describe in connection with physical activities like running may also be related to the production of endorphins. Conversely, addiction and tolerance to morphine (and other narcotic analgesics) are thought to be caused by suppression of the body's normal production of endorphins. When the effects of morphine wear off, withdrawal symptoms occur because there is a lack of normal endorphin molecules.
║Osteoporosis
Bones are comprised of fibers of collagen which provide elasticity, and calcium which provides strength. As a normal part of aging, bones tend to lose both collagen and calcium. This loss of bone density with age is more pronounced in women than in men. A person is diagnosed with osteoporosis when this bone loss becomes too great, leaving the bones brittle and prone to fractures. The above picture shows the spongy bone of a patient with osteoporosis. It is noticeably thinner than normal spongy bone.
The rate of bone loss is particularly high in women after menopause. This is because the ovaries stop producing the hormone estrogen which normally helps to maintain bone mass. Other causes of osteoporosis include a diet deficient in calcium and prolonged inactivity. Lost bone cannot usually be replaced, but measures can be taken to slow down the rate of bone loss. Treatment for osteoporosis is thus based on measures to help maintain the remaining bone. These measures include eating a diet high in calcium, increasing exercise, and estrogen replacement for post- menopausal women. Estrogen replacement has been proven to significantly reduce the incidence of fractures in post-menopausal women. The foods highest in calcium are milk and milk products, green leafy vegetables, citrus fruits, and shellfish. Calcium supplements are also useful.
As noted above, the development and maintenance of bone mass requires an adequate intake of calcium and phosphorus. However, the body cannot absorb these minerals without adequate Vitamin D. Osteomalacia is a softening of bones that occurs because of inadequate vitamin D. In children, osteomalacia is called rickets. Vitamin D is obtained both from the diet and from the action of sunlight on the skin. Osteomalacia thus results from a diet lacking vitamin D, a failure to absorb vitamin D, or insufficient exposure to sunlight. Unlike osteoporosis, osteomalacia is quite rare in developed countries.
Conception
The photograph above shows a portion of an ovum with many sperm all trying to fertilize it. This is the last step in the quest to reach the ovum. Only one of the sperm cells will successfully enter the ovum. The outer coating of the ovum is tough. However, the heads of the sperm cells contain a digestive enzyme which breaks down this coating to allow penetration. At the instant that one of the sperm cells breaks through, a reaction takes place which changes the outer coating of the ovum and prevents any more sperm from entering.
µPET Scan
One of the most modern techniques being used to study the brain is positron emission tomography (PET). The picture above shows a PET scanner. Superficially, the machines look very much like CT scanners, but on the inside they are quite different. A PET scan is accomplished by administering a small amount of a radioactive substance to a patient, waiting a short while, and then taking pictures to see where that substance has gone to. PET scanning thus reveals information about the function of the brain. This is different from simply looking at the structure of the brain as CT and MRI scanning do. PET has been used extensively by research doctors to try to figure out what parts of the brain are involved in many different neurologic illnesses including seizures, schizophrenia, and Parkinson's disease. PET has also been used to answer other interesting questions, such as what exact part or parts of the brain are involved in specific activities, like solving math or word puzzles.
∞The Placenta
The illustration above depicts the placenta. The placenta is a fetal organ which develops from the outermost cells of the embryo at its site of implantation in the uterus. The placenta serves as the method by which the developing fetus obtains oxygen and nutrients from the mother, and at the same time eliminates wastes. The structure of the placenta is based on numerous, tiny fetal blood vessels called chorionic villi. The chorionic villi are bathed in maternal blood within the placenta. This allows oxygen, food, and even small molecules like antibodies to freely move between the fetal and maternal circulations. Of note, however, the maternal and fetal red blood cells always stay separated. There is no mixing of the actual blood cells within the placenta. When the fetal blood returns from the placenta, it brings oxygen and needed nutrients with it from the mother. The connection between the placenta and the fetus is called the umbilical cord. This cord is clamped and cut soon after delivery. Throughout pregnancy, the placenta remains firmly attached to the uterus. However, the placenta loses its connection to the uterus within minutes following birth, and it is soon expelled. For this reason it is often called the afterbirth.
.Platelets
Platelets serve as the body's first line of defense to prevent excessive blood loss when a blood vessel is damaged. They normally circulate in the bloodstream in an inactive state. When platelets encounter a damaged vessel, however, they change their shape and become sticky. This causes them to adhere both to one another and to the damaged vessel wall. The illustration above shows a damaged blood vessel with numerous platelets (shown in yellow) rushing in to plug the hole. Platelets are the smallest of the three main types of blood cells. They typically last about nine days in the circulation. One of the many things aspirin does is inactivate platelets irreversibly, preventing then from sticking to one another. This effect is desirable in patients who are prone to forming unwanted blood clots.
OProstate Cancer
The prostate gland surrounds the urethra, sitting just below the bladder in men. Its normal function is to add secretions to semen. As men age, however, it is common for the prostate gland to enlarge. This enlargement may partly cut off the urethra, making it difficult to urinate. Usually, this enlargement is entirely benign, and it is treated only if the symptoms require that something be done. However, one must always be concerned that the changes in the prostate are due to cancer. Prostate cancer is one of the most common causes of cancer in men. Like breast cancer in women, it is a disease that has a good prognosis when it is discovered early and treated. In recent years, there has been a significant increase in the use of prostate cancer screening tests. It is hoped that this trend will save many lives in the future.
$Pulmonary Arteries
The photograph above shows a resin cast of the pulmonary blood vessels. The pulmonary vessels travel together with the airways, following the same course within the lungs. Like the airways, the pulmonary arteries branch again and again to form ever-smaller vessels. The smallest vessels are the pulmonary capillaries which travel through the alveolar walls. The capillaries then join together to form venules and then veins. There are four main pulmonary veins which return the newly oxygenated blood to the left atrium. Interestingly, the lung is the only organ besides the liver to receive a dual blood supply. In addition to the pulmonary arteries, which deliver only deoxygenated blood to the lungs, there are bronchial arteries which supply needed oxygen and nutrients to the lung tissues.
UPulmonary Embolism
Formation of blood clots in the leg and pelvic veins is a relatively common medical problem. These clots can then break off and travel to the lungs where they lodge in the pulmonary arteries. Blood clots in the lungs are called "pulmonary emboli." The illustration above shows severe damage to a lung segment served by an artery which is blocked by a pulmonary embolus. Pulmonary emboli can be life-threatening if they block too much of the blood flow to the lungs. Pulmonary emboli are responsible for more than 50,000 deaths in the U.S. each year.
The strongest risk factor for pulmonary emboli is physical immobility. Patients who are confined to bed after a major operation are at particularly high risk for a pulmonary embolus. Blood thinners are given to people who either have pulmonary emboli or are at high risk for developing them.
cBreathing Test
The photograph above shows a machine used to perform breathing tests. These pulmonary function tests can help in the evaluation of lung disorders such as asthma, emphysema, or cystic fibrosis. Pulmonary function tests can also be used to help determine whether treatment for an illness is working as desired. The machine works largely by measuring the volumes of air moving in and out as the patient breathes. A technologist explains what to do during the test. Sometimes, a blood sample is obtained at the same time as the breathing test to assess how well the lungs are supplying the blood with oxygen.
ÄThe Cerebellum
The cerebellum is the rounded brain structure which lies beneath the cerebrum and behind the brain stem. It has many deep and narrow fissures which increase its surface area six-fold. The primary role of the cerebellum is to maintain balance and to coordinate voluntary movement. The cerebrum initiates movements like walking or dancing, but the cerebellum is required to make these complex motions work correctly. People with cerebellar disorders have problems such as a staggering gait, hand tremors, and slurred speech. Interestingly, alcohol inhibits cerebellar function. For this reason, drunk people usually exhibit symptoms quite similar to people with cerebellar disorders.
The photograph above shows what the cerebellum looks like under the microscope. It is seen to be organized into three main layers, with the largest cells found in the middle layer. These large cells are called Purkinje's cells. The Purkinje's cells each connect with as many as 100,000 other nerve cells. This very intricate interaction with other parts of the brain enables the cerebellum to fine tune the commands which start within the cerebrum in the motor cortex.
╠Radiation Therapy
Radiation therapy is widely used in the treatment of cancer. Depending on the type of cancer, it may either be used by itself or in conjunction with other forms of therapy. The photograph above shows a machine that is used to deliver radiation therapy. Initially, doctors will calculate the correct dose of radiation needed to kill the cancer cells without unduly damaging normal, healthy tissue. Next, they calculate the best angle from which to direct the x-ray beams. Finally, marks are made on the skin, and a number of separate radiation sessions are performed. There is generally no discomfort involved. For cancer types that respond well, radiation therapy is an extremely useful method of treatment.
╘Red Blood Cell
The picture above shows a single red blood cell. Red blood cells function by carrying oxygen to every part of the body, and then carrying carbon dioxide back to the lungs. Red blood cells are very well designed to perform this important job. First, they are packed full of hemoglobin, which functions as the oxygen carrier. Interestingly, red blood cells have no nuclei, a feature which makes even more room for hemoglobin. Second, they are shaped like disks. This shape greatly increases their surface area compared with a sphere of the same volume. The large surface area is important because it improves the efficiency of oxygen transfer between hemoglobin and the tissues where the oxygen is needed. Red blood cells are formed in the bone marrow, and they have an average life span of about 120 days. After this period of time, red blood cells tend to become misshapen and they are removed from the circulation by the spleen.
Red cells normally comprise about 40% of the blood volume. When doctors measure this number, it is called the hematocrit. Sometimes the number of red blood cells drops too low. This condition is called anemia. Most generally, anemia results either because too few red blood cells are being made, or because they are being destroyed prematurely. The most common cause for underproduction of red blood cells is iron deficiency. Iron is a necessary component of hemoglobin, so iron deficiency results in inadequate formation of new red blood cells.
¬Diabetes
Diabetes mellitus is a common disorder caused by insufficient insulin production. Without adequate insulin, the body fails to use glucose (sugar) properly. The blood sugar level rises in the blood, and the extra blood sugar is eventually spilled into the urine. This leads to the classic symptoms of increased urination and excessive thirst. There are two main types of diabetes, insulin dependent diabetes (type 1), and non-insulin dependent diabetes (type 2). Type 1 diabetics are usually diagnosed between the ages of 10 and 16. In these people, the pancreatic cells that normally make insulin are completely destroyed. As the name implies, these people must receive replacement insulin in order to avoid severe symptoms. Even with regular insulin replacement and tight control of their blood sugar level, most type 1 diabetics develop complications over the years. The most common problems include retinal damage, kidney damage, general nerve damage, and higher than normal rates of atherosclerosis. The illustration above shows an eye that has sustained some damage to the retina because of diabetes. The reason for all these long term problems is not completely understood. Type 2 diabetics are quite different. They develop their disease gradually, and they can usually be treated with diet modification. Medications are also available if necessary. These people tend to be obese, and they are much older than type 1 diabetics.
¼The Retina
The retina is the light sensitive surface at the back of the eye. The photograph above shows a picture of the retina as taken with an instrument called an ophthalmoscope. The retina contains a vast number of specialized nerve cells called rods and cones that convert light rays into nerve signals. The cones provide color vision, and are most concentrated at the fovea. The fovea can be seen in the photo above as the region on the left side without any blood vessels crossing it. Because of their dense concentration, the cones in the fovea provide the finest resolution vision. The rods are much more sensitive to light than the cones, but they only provide black and white vision. Next time it is dark out, notice that you only see in black and white. All of the rods and cones connect with nerves whose signals exit from the eye via the optic nerve. The optic nerve, along with the retinal artery, pierces the eye at the optic disk. The optic disk is visible in the picture above on the right side. There are no rods or cones in the optic disk which creates a small blind spot on the retina. It is possible to demonstrate this blind spot, but people are not normally aware of it.
wIntestinal Virus
The illustration above shows a single rotavirus. Worldwide, it is one of the most common viruses that can infect the digestive system and cause gastroenteritis. The rotavirus is easily spread from person to person in a family or other group setting. Rotaviruses are also found in a number of animal species. Rotavirus infection is particularly problematic in infants and young children, and it is responsible for many deaths in undeveloped countries were medical care is inadequate. The rotavirus causes illness by invading the lining of the duodenum and the upper small intestine. The intestinal villi are transiently damaged, but they rapidly regenerate their lining. Illness typically begins with one or two episodes of vomiting followed by diarrhea. Uncomplicated cases resolve in about one week. Treatment requires only rest and adequate fluid intake to prevent dehydration.
`Jonas Salk
In the mid-20th century, polio raged as a major health problem. Polio is caused by an infectious virus that brings on paralysis and disability by damaging nerve cells. In 1954, Jonas Salk and his colleagues were able to build on the work of Edward Jenner by demonstrating that people who were exposed to a killed polio virus preparation would develop lasting immunity to the disease. The picture above shows Dr. Salk administering this vaccine to a child. The Salk polio vaccine was widely used between 1956 and 1960 in the United States, with dramatic results. In the early 1960's, a second polio virus vaccine was developed by Dr. Sabin. It consists of live but severely weakened polio viruses that can induce immunity but cannot cause disease. The chief advantage of this vaccine is that it can be administered orally rather than requiring injection.
Sickle Cell Disease
Many different disorders of hemoglobin production have been discovered. In general, these disorders are divided into problems with heme production (porphyria), and disorders of globin production. Disorders of globin chain production are called "hemoglobinopathies." Hemoglobinopathies can be further divided into those in which abnormal globin chains are produced in normal quantity, and those where normal globin chains are made in inadequate quantity (thalassemias). One of the most common hemoglobinopathies is sickle cell disease. Sickle cell disease is an illness that results from a single small substitution in the hemoglobin beta chains. These modified hemoglobin molecules have a tendency to clump and distort the usual smooth shape of the red blood cells.
├
Electricity in the Brain
The constant activity within the brain produces characteristic electrical signals that can be recorded with an EEG (electroencephalogram) machine. The technique for recording these brain waves has been used in medicine since 1928. It is a simple, painless test that takes only about an hour. A number of small electrodes are placed on the scalp and connected to a recording device. Recordings are usually made with the patient at rest, with the eyes open and shut, during and after hyperventilation, and while looking at a flashlight. All of these situations produce characteristic looking brain waves.
An EEG is most frequently obtained for people who are suspected of having a seizure disorder (epilepsy). Epilepsy is a common disorder that results from unorganized electrical discharges in the brain. About 1 in 200 people have epilepsy. There are a few different types of seizures. Grand mal seizures are the type that people are most familiar with. During a grand mal seizure, the chaotic electrical activity spreads to the whole brain causing the patient to lose consciousness and fall down, often with wild jerking motions. Other types of seizures, including absence seizures and partial seizures, are much less dramatic. Contrary to folklore, it is a bad idea to place anything (like a tongue protector) in the mouth of a person having a grand mal seizure. Loosening of tight clothing around the neck, and placement of something soft beneath the head are the only things that a bystander should do. An ambulance should be called if it is a person's first seizure ever, the seizure continues for more than five minutes, or another seizure follows soon after the first.
In addition to evaluating seizures, EEG machines have been used extensively to study sleep. EEG recordings of people during sleep show two grossly different patterns. One pattern is produced during REM (rapid eye movement) sleep, and the other during NREM (nonrapid eye movement) sleep. These sleep types are named this way because the eyes actually do flutter rapidly when people are in REM sleep. During REM sleep, the brain becomes very active electrically, producing an EEG pattern similar to that of an awake person. In contrast, the electrical activity slows down dramatically in NREM sleep. NREM sleep produces much lower frequency waves on an EEG recording. Normal sleep is characterized by alternating periods of NREM and REM sleep. Adults spend about 80% of their sleeping time in NREM sleep, but the periods of REM sleep become longer and more frequent as sleep continues. People awakened during REM sleep often report vivid dreams. Sleep appears to be a fundamental human requirement, but its exact function remains poorly understood.
╦Sperm Production
The male sex cells are called "sperm." They each have a tiny head containing the genetic material, and a long tail used to swim towards an egg cell. Sperm cells are quite small, measuring only 0.002 inches (0.05 millimeters) in length. Sperm are produced by the testes in a process referred to as spermatogenesis. This process begins in the seminiferous tubules and is completed in the epididymis. The original cells from which the sperm grow contain 46 chromosomes in humans. By a special division called "meiosis," this number is cut in half so that the sperm cells contain only 23 chromosomes. These 23 chromosomes can then unite with an egg, also containing 23 chromosomes, to make a new individual.
╟Skeletal Muscle
There are more than 600 skeletal muscles in the body. Skeletal muscles are also called "voluntary muscles" because they are responsible for purposeful movement of the body such as running and jumping. The photograph above shows a skeletal muscle fiber. The brain sends signals to each and every skeletal muscle fiber, enabling us to perform actions when we wish to do them.
There are three different types of muscle in the body: skeletal muscle, smooth muscle, and cardiac muscle. All three types of muscle are composed of fibers that permit movement through coordinated contraction and relaxation. At the microscopic level, the three types of muscle share a common mechanism for contracting. The basic working elements are actin and myosin filaments. When a muscle contracts, the individual myosin filaments slide over the actin filaments much like an extendable ladder does when it closes. This action causes the overall length of the muscle to shorten.
σBlood Smear
A blood smear is obtained by placing a drop of blood on a glass slide and smearing it to thin it out. The blood smear is then treated with special stains to make the blood cells easier to see. After drying, the blood smear is examined under the microscope to inspect for any abnormal cells. The picture above shows a section from a blood smear containing only white blood cells. When examining a blood smear, it is important to look at both the total number of white blood cells and the relative proportions of the different types of white blood cells. Either or both of these things will usually be abnormal in patients with a serious infection or with leukemia. Of course, there are many other reasons for abnormal white blood cell counts that are more benign. Besides examination of the white cells, it is important to look at the red cells for abnormalities. Sickle cell disease and malaria are just two of many blood diseases that are best diagnosed by looking at the blood smear.
Smooth Muscle
Smooth muscles are found within the organs and blood vessels. They are responsible for many body functions such as movement of food through the digestive tract, and contraction of the uterus during childbirth. As evident in the photograph above, smooth muscles are much less organized than skeletal or cardiac muscle. They are comprised of spindle-shaped cells that are grouped in bundles. Smooth muscles are also referred to as "involuntary muscles" since they are not under conscious control. Instead, they are controlled by the autonomic nervous system. The autonomic nervous system allows the brain to control many body functions without requiring conscious thought. Digestion, blood pressure, and temperature regulation are examples of such body functions.
ôSwimming Sperm
The photograph above shows a single sperm cell, close up against the wall of the uterus. The sperm cell at this point has already survived a major part of the long journey toward the ovum. Of the 300 million sperm that begin the quest, most succumb to the inhospitable environment within the vagina. Many more sperm are lost while trying to navigate through the mucus which blocks the passage through the cervix into the uterus. Those sperm that make it this far continue to swim upwards toward the fallopian tubes and the waiting ovum. Half of the sperm will inevitably enter the wrong fallopian tube but, of course, half of them will stay on track.
{The Spinal Cord
The spinal cord travels down from the brain through the center of the spine. All communication between the body and the brain travels through the spinal cord. The brain and the spinal cord together make up the central nervous system (CNS). The picture above shows a cross-section through the spinal cord. In the middle, there is a dark, butterfly shaped region called the grey matter. Surrounding the grey matter is the white matter.
The grey matter contains all of the nerve cell bodies. These nerves cells include motor neurons and interneurons. Motor neurons are involved with directing movement. Each motor neuron does this job by sending a single long projection (axon) out into the periphery to direct the activity of muscle fibers. Interneurons are contained entirely within the CNS. They function by conveying messages between other neurons. Sensory neurons are a third type of nerve cell. These neurons have their cell bodies outside the spinal cord, but they send processes into the spinal cord to communicate important sensory information such as temperature, pressure, and pain.
The white matter is comprised of nerve fiber tracts. These tracts are of two basic types. Ascending fiber tracts travel up to the brain to convey sensory information. Descending tracts travel down from the brain to convey motor signals. These tracts are necessary for normal sensation and movement throughout the body. Damage to the spinal cord at any level tends to cause loss of sensation (anesthesia), and loss of movement (paralysis) below the level of the injury. Oftentimes, these problems are permanent because spinal cord neurons are unable to regenerate if the are damaged.
There are 31 pairs of spinal nerves that branch off from the spinal cord. One pair of these nerves leaves the spine at every level from the first cervical vertebrae to the coccyx. The spinal cord itself ends at the level of the first or second lumbar vertebrae, but the spinal nerves continue to travel downward so that one pair leaves at each level of the spine. The tangle of nerves below the end of the spinal cord is called the cauda equina or "horse's tail."
îStroke
Stroke occurs when the blood supply to part of the brain is cut off for long enough to cause the death of that part of the brain. This does not take very long. Neurons in the brain can only live for about four minutes without oxygen. Another condition closely related to stroke is transient ischemia attack (TIA). A TIA initially seems like a stroke, but the symptoms quickly disappear. TIA's occur when the blood supply to a part of the brain is interrupted for long enough to stun the affected cells, but then restored before cell death occurs. Strokes are fatal in about a third of all cases, a percentage similar to that observed with heart attacks. For the survivors, a stroke can be quite devastating due to the loss of important brain functions. Sometimes, however, another part of the brain is able to take over the functions of the lost part of the brain.
The risk factors for having a stroke are generally the same as those for having a heart attack. The most notable are high blood pressure and atherosclerosis. A recent heart attack is itself a risk factor for stroke because of the tendency for blood clots to form in the heart and then travel upwards to the brain. Several studies have shown that aspirin taken every day can decrease the chances of a having a stroke in patients who have previously suffered from a stroke or a TIA. Aspirin works in this way by preventing blood clots from forming. It has also been shown that a small dose of aspirin every day can decrease the rate of heart attacks, even in patients who have not previously had any symptoms. Many doctors thus recommend that their patients take a single baby aspirin every day.
aNerve Communication
At their end, nerve axons usually branch into many small terminals which come into close contact with the dendrites of other neurons. The connection between two neurons is called a synapse. The axon and the dendrite never actually touch. There is always a small gap called the synaptic cleft. The photograph above shows a synapse. When an electrical signal reaches a nerve terminal, it causes the nerve to release neurotransmitters. Neurotransmitters are chemicals which travel the short distance to the nearby dendrites. The neuron that releases the neurotransmitter is called the pre-synaptic neuron. The neuron receiving the signal is called the post-synaptic neuron. Depending on the type of neurotransmitter released, the post-synaptic neurons are either encouraged (excited) or discouraged (inhibited) from firing. Each neuron communicates with many other neurons at the same time. Since all a neuron can do is fire or not fire, its behavior is always based on the balance of excitatory and inhibitory influences acting on it at that moment. Neurons are able to refire up to several times per second.
┐Male Reproductive System
The illustration above shows part of the male reproductive system. Sperm production begins in the innumerable seminiferous tubules within the two testes. A close-up of a seminiferous tubule is shown along with a developing sperm cell. Sperm then move into the epididymis where they mature. Shortly before ejaculation, the mature sperm are propelled from the epididymis into a long tube called the "vas deferens." The vas deferens carries the sperm to the seminal vesicles, which add seminal fluid to the sperm cells. The semen then travels along two short ducts to the urethra. Lastly, the urethra passes through the prostate, which adds more secretions to the semen before it leaves the body.
╛Thrombus
A platelet plug is merely the first step in the process of stopping blood loss when a blood vessel is damaged. The activated platelets and damaged vessel walls also secrete chemicals which begin the blood coagulation process. This process is a complex cascade that results in the formation of fibrin strands. The picture above shows a number of red cells trapped within a mesh of fibrin strands. This mesh is referred to as a thrombus. The coagulation cascade is designed to permit significant amplification of the signal to clot. Activation of just one molecule of the first factor in the cascade can result in the formation of 30,000 fibrin molecules at the site of the injury. At the same time, it is important that blood clots do not form when they are not needed. There are also anti-coagulation (thrombolytic) factors in the blood that rapidly dissolve inappropriate clots. A delicate balance between the pro- clotting and anti-clotting mechanisms is always maintained.
There are a large number of clinical disorders affecting the coagulation mechanism. The most well known is hemophilia, a disease that is present in about 1 in every 10,000 males born. It is caused by a lack of factor 8, one of the chemicals in the coagulation cascade. Without this factor, the cascade fails and fibrin strands are not formed. Hemophiliacs thus suffer from frequent and severe bleeds. Treatment involves the administration of the missing coagulation factor 8.
/Spongy Bone
Bones are not simply solid. Beneath the hard outer shell of compact bone, there is a core composed of spongy bone. The complex structure of spongy bone is shown in the photograph above. The gaps in the spongy bone are filled with a soft fatty tissue called "marrow." Bone marrow can be either red or yellow in color, depending on how much fat is found within it. Red bone marrow is responsible for producing most of the blood cells within the body. At birth, all the bones of the body contain red marrow. As we mature to adulthood, much of the red marrow is replaced by the more fatty, less active yellow marrow. This is most notable in the long bones of the arms and legs. In adulthood, red marrow is limited mostly to the skull, spine, shoulder blades (scapulae), clavicles, ribs, sternum, and pelvis.
╓ The Tracheal Lining
The photograph above shows a portion of the tracheal lining. The lining consists of two main types of cells, goblet cells and ciliated cells. The goblet cells secrete a sticky mucus which coats the respiratory lining and traps foreign particles that come from the air we breathe. The ciliated cells have numerous tiny hairs (cilia) on their surfaces which continuously beat in unison. This action sweeps the sticky mucus with its trapped particles up and out of the lungs.
Of note, cigarette smoking is very toxic to the cells which line the respiratory tree. The smoke kills many of these cells and causes inflammation of the airways. The normal protective function of the respiratory lining is thus impaired. This condition is called bronchitis. The chronic coughing and increased susceptibility to upper respiratory infections seen in smokers is due to bronchitis. Other causes of bronchitis besides cigarette smoking include infection with either bacteria or respiratory viruses, and inhalation of toxic chemicals.
Cystic fibrosis (CF) is another cause of bronchitis. It is an inherited disease that is caused by a defective gene. People who inherit a single copy of the CF gene from one of their parents, and a normal copy of the gene from their other parent, are called carriers. CF carriers can pass on the gene, but they exhibit no symptoms. In contrast, people who inherit two copies of the CF gene, one from each of their parents, develop cystic fibrosis. The CF gene is thus called a recessive gene. The tracheal lining in cystic fibrosis patients secretes mucus that is much thicker than normal. The ciliated cells are unable to sweep out this mucus and the airways tend to get clogged up. Cystic fibrosis patients suffer repeated bouts of bronchitis and pneumonia that results in permanent lung damage. This lung damage includes the formation of both cysts (dilated airways) and fibrosis (scar tissue), hence the name of the disease. The CF gene is quite common in the caucasion population, about 1 in every 22 people are carriers. This means that both the man and the woman will be carriers in about 1 in every 500 couples. One-quarter of the children from these couples will inherit the abnormal CF gene from both parents. This accounts for the finding that about 1 in 2000 babies born to white parents have cystic fibrosis. Of note, tests have become available in recent years to determine if a person is a CF carrier, and whether an unborn baby will develop the disease.
≤Tuberculosis
Tuberculosis is an infectious disease commonly referred to as TB. It is caused by a bacteria which is spread from person to person by airborne droplets either coughed or sneezed up. The bacteria are breathed into the lungs where they begin to multiply. The TB bacteria prefer very well oxygenated environments. Consequently, they have a marked preference for the upper lobes of the lungs where the oxygen level is relatively higher than it is in the lower lobes. In most cases, the body's immune system arrests the infection and healing occurs. In some cases, however, the infection remains unchecked and goes on to spread to other organs. This widespread infection is called miliary tuberculosis, and it has a poor prognosis. In another small percentage of cases, the infectious organisms remain viable within the lungs, but adequately walled off. Later in life, the infection can then resurface when the immune system becomes compromised by age or disease.
Until recently, the incidence of TB had declined in western countries throughout the 20th century. The invention of antibiotics had a monumental impact in the mid-20th century, bringing about a precipitous decline in new cases of TB. Antibiotics also revolutionized therapy, which at that time consisted either of nothing or radical surgery. Unfortunately, TB has been making a resurgence in recent years. This is attributable to the rise of the AIDS virus. Patients with AIDS are at high risk for developing TB because of their immuno- compromised condition. Also, unlike AIDS itself, TB is a very infectious illness that is easily transmitted to others in the community. If this weren't enough, new strains of TB are emerging that are resistant to all the standard antibiotic regimens used to treat TB. It is unclear how large this modern health problem will become. In the meantime, it is prudent for high risk individuals, such as hospital workers, to be skin tested for TB regularly, and to take antibiotics if their TB skin test becomes positive.
╤Twins
Two babies sometimes result from a single pregnancy as shown in the illustration above. Twins can be either identical or fraternal. Identical twins develop from a single ovum which splits into two groups of cells soon after fertilization. Identical twins are also called "monozygotic twins," meaning one zygote. Monozygotic twins always look remarkably similar because they are genetically identical. Fraternal twins develop from two separate ova which are each fertilized before implanting in the uterus. Fraternal twins are also called "dizygotic twins," meaning two zygotes. Dizygotic twins may or may not be of the same sex since they are quite independent of one another. The frequency of twin births is about 1 in 90 pregnancies. Dizygotic twins are more likely to occur in women who have a family history of twins, and women who have had many babies before. In contrast, the development of monozygotic twins is random, and these factors do not play a role.
NThe Ureters
The ureters are the long muscular tubes which connect the kidneys to the bladder. Like the intestine, the walls of the ureters contain smooth muscle which contracts in rhythmic fashion to propel the urine down into the bladder. These rhythmic contractions are called "peristalsis." There is a one-way valve at the entrance of each ureter into the bladder. These valves prevent urine from backing up into the ureters and the kidneys. Occasionally, these valves may not work properly, leading to reflux (backwards flow) of urine. This is the most common cause of kidney infections.
Ultrasound
Ultrasound examinations have become a very routine part of pregnancy. The photograph above shows a picture of an ultrasound probe. This hand-held device emits high frequency sound waves that bounce off the developing fetus and other internal structures. The probe then "listens" for the returning echoes to form an image. These sound waves are of very low energy, and the technique is entirely safe. Ultrasound waves do not penetrate well through air. For this reason, a gel is always used to improve the contact between the probe and the person being scanned. Also, with fetal ultrasound, the examination works better if the mother has a full bladder. The full bladder serves as an ultrasound window to see the fetus through, since the sound waves travel so well through the fluid. Although routine prenatal scanning has become commonplace, studies are beginning to show that there is no measurable difference in the overall pregnancy outcome between groups of women who all have ultrasound examinations and similar groups of women who don't.
╓Heart Valve
The pumping action of the heart depends on the proper function of the heart valves. There is a single one-way valve at the exit of each of the four chambers. Beginning on the right side of the heart, the four valves are the tricuspid valve, the pulmonary valve, the mitral valve, and the aortic valve. The closing of these valves is responsible for the characteristic "lubb dupp" sounds made by the heart when it beats. The first sound occurs when the tricuspid and mitral valves close. The second sound occurs when the pulmonary and aortic valves close.
The valves are held in place partly by small muscles called papillary muscles. The picture above shows part of the mitral valve and one of its papillary muscles. Generally the valves last a lifetime, but they sometimes become damaged. Any of the valves can become either too leaky (regurgitant), or too tight (stenotic). Regurgitant valves stress the heart by allowing the blood to flow partly backwards. Stenotic valves stress the heart by resisting the normal forward flow of blood. Conditions that can damage the valves include rheumatic fever and endocarditis. If a heart valve becomes damaged enough, it is generally best to replace it with an artificial valve.
?Circulation
One of the landmarks in medical history was William Harvey's discovery that blood flows through the body in a continuous, closed loop. The circulation begins with the left ventricle pumping blood into the aorta, the body's main artery. Next, the aorta goes on to branch again and again to form smaller and smaller arteries. The smallest arteries are called arterioles. The arterioles connect with the capillaries which are no wider than a single blood cell. The red blood cells travel slowly through the capillaries in a single file line. This allows the blood cells to come close to the walls of the capillary in order to release their oxygen and pick up carbon dioxide. The capillaries then come back together to form tiny venules. Finally, the venules join together to form veins that carry the blood back to the heart. Once arriving in the heart, blood cells travel on a very similar journey through the lungs. In the lungs, blood cells course through tiny pulmonary capillaries where they release carbon dioxide, and pick up oxygen in preparation for beginning the circulation through the body once again.
The high pressures generated by the left ventricle keep the circulation moving forward through the arteries. The pressures are much lower, however, on the venous side of the circulation. Instead of relying on the heart, circulation on the venous side depends mostly on the contraction of skeletal muscles which squeeze the veins and push the blood forward. Blood always moves forward because there are one way valves within the veins that keep the blood from backing up.
Health and Diet
More and more, people are recognizing the important relationship between health and diet. Many of the most common health problems in Western society have been proven to be diet related. Most notable is atherosclerosis which leads to both heart attacks and strokes. Many forms of cancer appear to be linked to diet as well. Although opinions change as to what the optimal diet should be, it is clear that a low-fat diet reduces the incidence of atherosclerosis and may reduce the incidence of some cancers. Most people agree that a diet high in complex carbohydrates including fruits, vegetables, and grains is best. Meat and dairy products are fine, but needn't be the main part of one's diet. Total fat intake should be kept to only 15% of total calories, if possible.
úLung Scan
The most common method used to try to diagnose blood clots in the lungs is a lung scan. This test is relatively easy to perform. It involves administering a small volume of tiny, radioactive particles that travel to the lungs through the blood. These particles become trapped in the small blood vessels (arterioles) just before the pulmonary capillaries. The picture produced from the radioactive particles shows a normal outline of the lungs, unless there are blood clots which block the blood flow to certain lung segments. In this case, there are wedge-shaped defects where the particles didn't reach the lung tissue because of the blockage. It is also routine to do a breathing test with a radioactive gas. This enables doctors to see if any parts of the lungs are not receiving air. Quite frequently, it turns out that the cause for a person's shortness of breath is a blocked airway instead of a blocked blood vessel.
┐ White Blood Cell
The principal role of white blood cells is to protect the body from infection. There are three main types of white blood cells, each of which plays an important role in the immune system. The three types are granulocytes, monocytes, and lymphocytes.
Granulocytes, the first of the three classes of white blood cells, are themselves divided into three more types. Neutrophils are the most important of these types. Basophils and eosinophils are the other two. A neutrophil is shown in the picture above. Neutrophils have the job of defending the body against invading bacteria. Neutrophils perform this job by simply engulfing the bacteria and killing them. Neutrophils are also called phagocytes, a term which means "engulfing cell." The pus that accumulates at the site of an infection consists almost entirely of neutrophils.
Monocytes are the next major class of white blood cells. Like neutrophils, monocytes are also phagocytes. However, monocytes are much less particular about what they will engulf. Monocytes are required to remove the cellular debris that persists long after a typical infection has been cured.
The last major class of white blood cells is lymphocytes. Lymphocytes are formed both in the bone marrow and in the lymph glands. Lymphocytes are usually divided into B-cells and T-cells. B-cells are responsible for making antibodies. Antibodies are special molecules that are tailor made to bind to nearly any foreign material that enters the body. Once formed, the antibodies help the body to eliminate these foreign materials. The other type of lymphocyte, T-cells, have two main jobs. The first of these jobs is to assist the B-cells with making antibodies. The second job is to recognize and eliminate cells that seem foreign to the body. T-cells are responsible when an organ transplant is rejected. T-cells are also responsible for eliminating otherwise normal cells that have been infected with a virus. This happens because the infected cells have virus particles on their surfaces which make them seem foreign to the body.
Lymphocytes (B-cells and T-cells) are usually very good at distinguishing the body itself from foreign invaders. This is called self tolerance. Occasionally, this process goes awry, and the lymphocytes attack the body as if it was a foreign object. Many different disorders can result from this mistaken immune system behavior. Collectively, these disorders are all referred to as autoimmune diseases.
âAlveoli
The alveoli are the tiny air sacs in the lungs where red blood cells pick up oxygen, and release the waste product carbon dioxide. The photograph above shows several alveoli. Note the thin alveolar walls. The red blood cells are contained within tiny pulmonary capillaries that course through the alveolar walls. The red blood cells tend to flow in single file lines through the pulmonary capillaries. Because of the thin walls, the red blood cells come into very close contact with the air. Both of these things promote efficient transfer of oxygen and carbon dioxide between the red blood cells and the air within the alveoli.
Under normal circumstances, the alveoli form an enormous surface area for gas exchange to take place within the lungs. However, there are many diseases which disrupt this process. Heart failure is one which causes some of the alveoli to fill up with water, preventing air from getting near the red blood cells. Pneumonia causes a similar problem by filling up some of the alveoli with pus. Over time, cigarette smoking can also seriously damage the alveoli, leading to a disease called emphysema. In this case, it is the alveolar walls which are injured. Eventually, large segments of alveoli disappear entirely, leaving behind air pockets called bullae. No gas exchange occurs in these large air pockets in the lungs, and patients can become quite short of breath.
Alzheimer's Disease
Alzheimer's disease is a progressive brain disorder in which brain cells degenerate and the brain substance shrinks. The picture above shows the appearance of a brain from an Alzheimer's patient. Note how the folds are much more open than in a normal brain. The progressive nature of the disease causes patients to become increasingly forgetful and disoriented as time goes by. It is by far the largest cause of dementia in elderly people, but its cause remains unknown. There is no treatment for Alzheimer's disease beyond caring and appropriate support for those suffering from the disease. It is important to look for other causes in patients suffering from dementia, however, since approximately 10% of elderly people will prove to have some other treatable cause for their symptoms.
^Amniocentesis
Amniocentesis is a diagnostic procedure in which a small volume of fluid is withdrawn from the amniotic sac. The amniotic sac is the membrane within the uterus that surrounds the fetus. This procedure is done quite carefully while watching the tip of the needle with ultrasound. The amniotic fluid contains fetal cells which can be grown and then analyzed. In particular, doctors and patients are interested in analyzing the chromosomes (DNA) of the developing fetus. Amniocentesis can only be performed between the 16th and 18th weeks in pregnancy. Also, the chromosome test takes about 2 to 4 weeks so its results may not be available until the 20th week. This is well into the second trimester. There is a slight increased risk of miscarriage (0.5%) as a complication of amniocentesis. It is generally only recommended for women over 35, who are all at a somewhat higher risk for having a child with Down's syndrome, or women who are at risk for having a genetically abnormal baby for some other reason. Another technique similar to amniocentesis is called chorionic villous sampling (CVS). This test involves using a needle to obtain actual cells from the chorion which surrounds the fetus, rather than just amniotic fluid. CVS can be performed much earlier in pregnancy, at about 12 weeks, but it has a higher risk (about 1-2%) of inducing a miscarriage.
Angina
When atherosclerosis affects the coronary arteries, it is called "coronary artery disease" (CAD). Patients with CAD experience chest pain when the blood supply to the heart is inadequate to meet the demand for oxygen. This pain is called "angina." CAD is a very common ailment with characteristic symptoms. Angina typically occurs after a predictable amount of exercise (e.g., walking up a flight of stairs), and is relieved by rest. Medication is available that relieves the pain by briefly dilating the coronary arteries, but this has no effect on the underlying disease. Patients with angina are at high risk for having a heart attack if their coronary artery disease is not treated.
The incidence of atherosclerosis is very strongly correlated with a number of risk factors. Three of the major risk factors are a diet high in fat and cholesterol, cigarette smoking, and inactivity. Fortunately, the progression of atherosclerosis can be significantly slowed, and sometimes even reversed, by modification of these lifestyle choices.
)Antibodies
This picture shows several Y-shaped antibody molecules within a blood vessel. Antibodies are made by the immune system to react with specific foreign invaders. Bacteria, viruses, and other microorganisms are all common pathogens that will usually elicit an antibody response. Once made, antibodies stay in the circulation for many years -- in some cases, even a whole lifetime. If an individual is re-exposed to a pathogen for which they have previously made antibodies, they will be able to eliminate the pathogen before it causes any problems.
╡Sports Injuries
There is a wide range of injuries that may result from athletic activity. Fractures, ligament sprains, muscle strains, and cartilage tears are just some of the injuries commonly encountered in the emergency room. The ankle is the joint most frequently sprained. This typically occurs when the ankle "turns over" and the ligaments are severely stretched. An x-ray is usually taken to exclude the possibility of a fracture. An ankle sprain causes significant pain and swelling. Treatment consists of ice-packs to reduce swelling during the first 24 hours, analgesics to relieve pain, and rest while the joint heals itself. Strain of the Achilles tendon, located at the back of the ankle, is another injury sometimes encountered.
Knee injuries are also commonly encountered in the emergency room. Football and skiing are two sports which place particularly great stress on the knees. Twisting motions can lead to serious ligament sprains, and/or tearing of the cartilage cushions (menisci) in the knee. Magnetic resonance imaging (MRI) and arthroscopic surgery have revolutionized the treatment of these injuries. With MRI it is often possible to determine the exact nature of the joint injury from the images alone. The orthopedic surgeon may then be able to repair the knee using arthroscopic surgery without ever having to open up the joint. The picture above shows a surgeon performing arthroscopic surgery. This technique involves placing an endoscope (a small, flexible, lighted viewing tube) into the joint through a small incision. Other tools such as tiny scissors or scalpels are also placed into the joint through small incisions. The surgeon then performs the operation with these tiny tools while watching what he or she is doing on a television screen. Like the knee, shoulder injuries are also frequently treated with arthroscopic surgery.
Muscle strains are another common injury that may result from vigorous athletic activity. Running, golfing, and tennis are all examples of activities that will sometimes cause strain of muscles or their tendons. Like ligament sprains, muscle strains are treated with ice packs to reduce swelling, analgesics to relieve pain, and rest to promote healing.
░Asthma
Asthma is a common illness, affecting about 1 in 20 people in the United States. There are two main types of asthma: extrinsic asthma, in which an allergen or some other external stimulus is responsible for attacks, and intrinsic asthma, in which there is no apparent cause for attacks. With either type, the main problem is inflammation and narrowing of the bronchioles. The inflammation leads to increased sputum production in the bronchioles which further narrows the airways. During an asthma attack, patients experience wheezing and extreme shortness of breath. Bronchodilators are the mainstay of therapy, once an attack has started. These medicines cause the narrowed airways to open up and allow more air in and out. The photograph above shows a patient using an inhaler containing a bronchodilator. Anti-inflammatory medicines are also an important part of therapy. These medicines are used to try to prevent asthma attacks.
SOn the Tip of a Pin
Bacteria are remarkably small. The photograph above demonstrates their size relative to the tip of a pin. The immune system is usually adequate to allow recovery from exposure to bacterial illness. The advent of antibiotics, however, has revolutionized the treatment of serious bacterial illness that has not been controlled by the immune system. These medications work either by killing bacteria directly, or else by stopping their growth in order that the immune system can more effectively eliminate them. Unfortunately, bacteria frequently develop resistance to the antibiotics which once killed them. In effect, a war has begun between the scientists that keep developing new antibiotics and the bacteria which seem to develop resistance to those antibiotics at an ever increasing rate. The most simple explanation for emerging resistance is selection pressure. If only one in a large number of bacteria is resistant to a drug, then all the other organisms will be killed, and the resistant cell will multiply to replace the dead bacteria. This process occurs because bacterial reproduction is so rapid, occurring about once every 20 minutes. After 6 hours, a single bacterium can regenerate a population of a million. This is a strong argument against the indiscriminate use of antibiotics which only leads to more and more resistant strains.
!Bacteria
Bacteria are a very large group of single-cell microorganisms. Bacteria were first discovered with the advent of the microscope in the 17th century. However, it was not until Louis Pasteur studied them in the mid-19th century that it became clear that bacteria were responsible for many human diseases. The picture above shows a single bacterium of the salmonella type. This bacteria often causes fever and diarrhea in humans. Note that it has a thick capsule, and flagella (hair-like structures) that it uses to move around. There are many ways to classify bacteria. One method is based on shape, of which there are three main classes. Cocci are spherical, bacilli are rod-shaped, and spirilla are spiral-shaped. Bacteria are also classified as being either gram positive or gram negative, based on whether they take up the gram stain that is commonly used to make them easier to see under the microscope. A third method of classification is whether they can live in the presence of oxygen (aerobic) or require the absence of oxygen (anaerobic).
MBall and Cage Valve
The second most common major heart operation in the western world is valve replacement. Any one of the four heart valves may become either so tight, or so leaky that it needs to be replaced in order to restore normal heart function. As a rule, valve replacement surgery has a very high success rate. Long term complications from rheumatic fever are still the most frequent cause of severe valve malfunction.
Many different types of artificial heart valves have been devised over the years. The picture above shows a mechanical ball and cage valve which has been widely used. Another popular mechanical valve uses either one or two tilting disks. It is also common to use tissue valves taken from pigs (porcine valves). Least commonly, valves can be taken from human organ donors. Mechanical valves last longer than porcine or human tissue valves, making them more suitable for younger patients. On the other hand, mechanical valves damage red blood cells more than tissue valves do, and they tend to cause the formation of blood clots. Because of this, all people with mechanical valves need to take anticoagulant medication (blood thinners) to prevent blood clots from forming. The choice of what type of artificial valve to use is thus a difficult question that must be decided for each individual requiring a valve replacement operation.
FBlood Cells
There are three main types of cells within the blood. These are shown in the picture above. From left to right, the picture shows a platelet, a white blood cell, and a red blood cell. The sizes are not to scale. A white blood cell is actually much larger than a red blood cell, and a platelet is much smaller than a red blood cell. Red blood cells are the most numerous by far, making up about 40% of the total blood volume. White blood cells and platelets are much less numerous, together making up only about 5% of the blood by volume. The remaining half of the blood is composed of a fluid called plasma.
Plasma is a sticky fluid that is 95% water. The other 5% is composed of the many substances that are dissolved within the plasma. These include nutrients, proteins, waste products, and hormones. Nutrients are the substances needed by the body's tissues to sustain their normal function. The principal nutrients are sugars, fats, amino acids, vitamins and minerals. All of these are dissolved within the plasma, and then delivered to each cell within the body. The primary proteins in the plasma serve either as part of the clotting mechanism, as part of the immune system, or as transporters for nutrients. The main waste product in the plasma is urea. It is a by-product of metabolism that is transported to the kidneys where it is eliminated. Hormones are chemicals that are used to regulate many of the body's functions. They are produced by the body's endocrine glands, and then released into the blood so that they may travel to their target organs elsewhere in the body.
ùBlood Bank
One of the great breakthroughs in the history of medicine was Karl Landsteiner's discovery of blood groups in 1901. Prior to this discovery, blood transfusions were hazardous at best, and oftentimes lethal. Landsteiner discovered two basic markers (antigens) that are often present on the surface of red blood cells. He named these two antigens A, and B. All people are either type A, type B, type AB, or type O; depending on whether they have one, both, or neither of these markers on their red cells. Landsteiner also discovered that plasma usually contains antibodies that can react with the A and B antigens on the red blood cells. Before giving a blood transfusion, it is necessary to determine that the recipient's plasma does not have any antibodies that will react with the donor's red blood cells.
These days, blood transfusions are very safe, and transfusion reactions are virtually unheard of. The more significant risk today is the transmission of a disease such as hepatitis or AIDS through a blood transfusion. This risk is very small, however, since all donor blood is carefully screened to make sure it is free from these infectious viruses. Nonetheless, it has become a common practice to donate one's own blood in advance of a scheduled operation, so that the chance of contracting an illness is reduced to zero. It is important to remember that blood can only be obtained from human donors. Donating blood is a very helpful thing that people can do for their fellow men and women. Also, it is good to bear in mind that it is impossible to contract any illness by donating blood. The picture above shows several units of blood packaged for transfusion.
≤The Human Brain
The largest and most developed part of the human brain is the cerebrum. The two massive cerebral hemispheres account for more than 70% of the weight of the entire brain. The photograph of a human brain shown above is dominated by the cerebrum, with its many deep folds. Also seen in the photograph are the cerebellum, located at the back of the brain, and the brainstem. The brain and the spinal cord together form the central nervous system (CNS). The CNS is the control center for the body. It gathers information about the environment and the body from the peripheral nervous system and then initiates appropriate actions.
The brain and spinal cord are surrounded by three membranes (meninges). The two outermost membranes (the dura and the arachnoid) are separated from the inner membrane (the pia) by a space filled with fluid. This fluid is called cerebrospinal fluid (CSF). The brain makes about 500 milliliters (1 pint) of CSF each day. The CSF bathes the brain and acts as a cushion for the brain during movement of the head. Lumbar puncture is a safe and common test done to examine the CSF. This test is done by placing a needle into the spinal canal, low in the back, below the end of the spinal cord. CSF can then be withdrawn from the spinal canal. CSF is normally a clear fluid, but it may become cloudy when there is an infection of the meninges.
Emerging from the brainstem are 12 pairs of cranial nerves. The cranial nerves are responsible for all of the functions of the head. These include such things as smell (cranial nerve 1), vision (cranial nerve 2), eye movements (cranial nerves 3, 4, & 6), facial sensation (cranial nerve 5), facial expressions (cranial nerve 7) hearing and balance (cranial nerve 8), taste (cranial nerve 9), and tongue movements (cranial nerve 12). Cranial nerves 10 and 11 are atypical. The 10th cranial nerve leaves the head and travels downward to all the major organs of the body where it influences their activity. Because of its wandering course, it is called the vagus nerve. The 11th cranial nerve also leaves the head, but it only travels as far as the neck where it helps direct neck movements. The skull has many little holes in its base which allow all the cranial nerves to travel to their destinations.
ëBrain Regions
Most brain functions have been found to be controlled by very specific regions of the brain. Voluntary movements are controlled by a part of the frontal lobes (the pre-central gyrus). Sensation is processed by an adjacent part of the brain in the parietal lobes (the post-central gyrus). Interestingly, the nerve pathways for both movement and sensation cross the midline. This causes the right side of the brain to control the left side of the body, and the left side of the brain to control the right side of the body. Most people have a dominant left brain, and are thus right handed. The right and left sides of the brain communicate across a large fiber tract called the corpus callosum. In a few rare cases, the corpus callosum has been cut surgically to control the spread of seizures from one side of the brain to the other. This can result in very unusual symptoms. An example is being unable to name an object held in the left hand because the signals can't cross back over to the left brain where the speech center is.
Speech is an important function controlled by two main regions of the brain, Broca's area and Wernicke's area. Broca's area is in the frontal lobe and is responsible for generating meaningful speech. People who sustain damage in Broca's area are often unable to say anything that makes sense, even though they are able to understand other people. Wernicke's area is necessary for speech recognition. Damage to Wernicke's area results in an inability to comprehend spoken language, a very disabling condition to be sure. Interestingly, the two speech centers are confined to only one side of the brain, typically the dominant left side. This is different then most brain functions which are handled by the analogous brain regions on both sides. Another important function of the brain is vision, which surprisingly, is processed at the very back of the brain in the occipital lobes.
(Newly Born
Breast-feeding is the natural method of feeding infants. It was, of course, perfected long before people ever came up with the idea of baby formula. Today, most doctors agree that breast milk provides the newborn infant with the ideal balance of nutrients. It also provides the baby with antibodies from the mother which help to prevent infections until the baby's immune system becomes stronger after a few months. There can be problems with breast-feeding including sore or cracked nipples, but these problems can usually be resolved without stopping breast-feeding. However, there are a number of legitimate reasons to choose bottle-feeding rather than breast-feeding. The choice not to breast-feed is one that a woman should make after consultation with someone knowledgeable about the subject.
≥Breech Babies
By the eighth month of pregnancy, most babies have assumed a head-down position. If the baby is not head down, then it is said to be in a "breech" position. It is sometimes possible to move a baby into the head-down position by pushing from the outside. If this is not successful, then the baby will often remain in the breech position throughout the remainder of the pregnancy and delivery. Breech deliveries are more difficult for both the baby and the mother because the baby's body does not mold a path through the pelvis as well as the head normally does. Some doctors will try to deliver a breech baby vaginally, while others prefer to perform a caesarean section for breech babies because it poses less risk to the mother and to the baby.
gThe Breast
The primary function of the female breast is to produce nourishing milk for a newly born baby. The female breast is well suited for this job. It consists of 15 to 20 lobes of milk secreting glands that are embedded in fatty tissue. The milk glands all empty into a network of ducts that exit the breast at the nipple. The production of milk is called "lactation." Lactation is maintained after delivery by the hormone prolactin, which is secreted by the pituitary gland. The breast contains no muscles. Instead, it is held up by fine ligaments that connect to the skin in front and the chest wall behind.
<Brain MRI
The images produced by modern magnetic resonance imaging (MRI) scanners are exquisite in their appearance. The picture above shows an image of the brain as seen with MRI. It reveals the underlying anatomy in detail previously only seen by pathologists working with anatomic specimens. The availability of this technology has significantly affected the practice of medicine. Many diseases are now readily diagnosed on the basis of MRI exams alone. On the other hand, their is still no substitute for sensible clinical judgement and a friendly, caring bedside manner.
₧Broken Bones
Fractures of the arm or leg are relatively common. An x-ray is usually taken when a fracture is suspected. X-rays were first discovered in 1896 by Wilhelm Conrad Roentgen. Each of the body's tissues absorbs x-rays in a predictable way. The bones are dense and absorb x-rays much better than the soft tissues, which are mostly made of water. An x-ray of the arm or leg is performed by placing the extremity between a piece of film and a tube which makes the x-rays. The x-ray tube is then turned on for a brief moment to expose the film. The bones absorb most of the x-rays, and thus appear white on the film. In contrast, most of the x-rays penetrate through the soft tissues to expose the underlying film and turn it dark grey. A radiologist then examines the film to determine if there is a fracture of one of the bones. A fracture is seen as a break in the normally smooth contour of one or more of the bones.
ªThe Small Airways
The small airways consist of the bronchioles and the alveoli. Structurally, the bronchioles are different from the larger bronchi because they lack cartilage within their walls. The terminal bronchioles are the smallest airways within the lungs. At their end, they branch into many small, grape-like sacs called "alveoli." The illustration above shows three clusters of alveoli branching from a terminal bronchiole.
±Coronary Bypass Grafting
The most common major heart operation in the Western world is coronary artery bypass grafting (CABG). Approximately 500,000 CABG operations are currently performed in the U.S. each year. This operation is recommended for treatment of severe coronary artery disease that is unsuitable for treatment with coronary angioplasty. The operation involves taking a blood vessel from the leg (saphenous vein), and using it to make new coronary vessels that bypass the narrowed segments of the patient's diseased coronary arteries. It is also typical to redirect one of the arteries from the chest wall so that it will supply the heart muscle instead. The illustration above shows a heart after several new coronary bypass grafts have been sewn in place.
)Atherosclerosis
Atherosclerosis is a disease which results in narrowed arteries and decreased blood flow. The arteries become narrowed because of a build-up of plaques within their inner walls. The picture above shows a yellow plaque within the inner layer of an artery. Plaques consist of a mixture of substances including cholesterol, fat, fibrous tissue, clumps of platelets, and sometimes calcium.
Atherosclerosis begins early in life, but generally causes no symptoms until middle or old age. This is because it takes many years for plaques to develop, and because normal arteries are much larger than they need to be. Only after an artery becomes very narrowed will blood flow be diminished enough to cause symptoms. When atherosclerosis affects the arteries supplying blood to the heart, patients experience intermittent pain called "angina." Likewise, when the arteries supplying blood to the legs are affected, patients experience intermittent leg pain called "claudication." Both angina and claudication are brought on by activity and are relieved with rest.
Cardiac Muscle
Cardiac muscle is found only in the heart. Cardiac muscle has the unique property of rhythmically contracting on its own without requiring any direct instructions from the brain. The brain, acting through the autonomic nervous system, serves only to influence the rate at which the heart contracts. Interestingly, heart transplants work only because the heart is able to contract without direct instructions from the brain. After a heart transplant, there is no connection between the brain of the recipient and his or her new heart.
aThe Large Airways
The large airways include the trachea (windpipe) and the bronchi. The first branching point in the respiratory tree is called the carina. The trachea divides at the carina to form the right and left mainstem bronchi which each enter one of the lungs. The photograph above shows the carina. The mainstem bronchi then divide to form the lobar bronchi. There are three lobar bronchi on the right side (upper, middle, and lower) and two on the left (upper and lower). The lobar bronchi go on to divide again and again into even smaller bronchi.
The photograph above was taken with an instrument called a bronchoscope. Like the endoscopes used to study the digestive system, the bronchoscope has a light and a camera lens at its end. It is different, however, since it is straight and rigid rather than flexible. The bronchoscope is most frequently used to look at the inside of the airways in order to help make a diagnosis. Surgical tools can also be manipulated through the bronchoscope, enabling direct treatment of some medical problems. Another common use of the bronchoscope is to pull out foreign bodies which have been accidently breathed in. Of interest, most foreign bodies wind up in the right lung because the right mainstem bronchus takes a relatively straight path down from the trachea, while the left mainstem bronchus branches at a sharper angle.
The Carpal Tunnel
The median nerve and the flexor tendons for the phalanges all travel through a narrow space in the wrist called the "carpal tunnel." The roof of the carpal tunnel is formed by a ligament called the "flexor retinaculum" which connects the carpal bones at the front of the wrist. Carpal tunnel syndrome occurs when repetitive hand and wrist motions cause swelling of the flexor tendons and squeezing of the median nerve. This impingement of the median nerve is the primary cause of the pain associated with carpal tunnel syndrome. Surgical treatment involves cutting the ligament which forms the roof of the carpal tunnel. This makes extra space and frees up the median nerve. Carpal tunnel syndrome can also be treated with braces which prevent excessive wrist motion.
ÉStudying the Heart
As a first step in the evaluation of patients with coronary artery disease (CAD), it is desirable to study the coronary arteries. Many different tests have been devised to do this. Some of these tests are simple and non-invasive like the stress EKG test. This test requires only that the patient exercise while being monitored with an EKG machine. The accuracy of this test is further improved if pictures of the heart are taken with a nuclear medicine camera during exercise and after resting. At present, the definitive test for evaluating the coronary arteries is angiography. Coronary angiography is an invasive test that requires placing a catheter in the coronary arteries. Dye is then injected, and detailed pictures of the coronary arteries are obtained. This test enables doctors to determine the exact location and severity of the plaques within the coronary arteries.
Several new forms of treatment for CAD have emerged in recent years. The most well accepted is coronary angioplasty which was first introduced in 1976. Coronary angioplasty involves positioning a small balloon catheter in a coronary artery such that the balloon spans a significant plaque. The balloon is then inflated to compress the fatty plaque and make it smaller. When the balloon is deflated, the plaque usually remains compressed. This increases the size of the arterial lumen (central opening), and improves blood flow to the heart. Other techniques for treating CAD utilize tiny catheters with either cutting blades to physically remove the plaque material, or lasers to vaporize the plaque material. Neither method has yet advanced to the stage of widespread acceptance.
÷First Steps
By a year of age, babies have generally mastered crawling and have begun walking around furniture while holding on (cruising). They may also be starting to take their first steps. Some babies are proficient walkers at this age, a skill that parents may soon find is a bigger problem than they had imagined. Twelve-month-old babies can grasp small objects and release them easily. Both hands are generally used without obvious preference. At this stage, objects are more likely to be dropped on purpose and then picked up once again rather than being placed in the mouth. Babies at this age will turn when their name is called and they begin to show some understanding of language. These babies will also demonstrate affection with familiar adults.
≡I Found My Toes
Children acquire physical and motor skills in specific stages called "milestones." There are, of course, wide variations between individuals, but general guidelines are useful to assess development. By six months, babies can usually roll over, and they can sit up with support. They are able to track objects with their eyes, and reach out toward those objects. Once grasped, objects may be transferred from one hand to the other, or brought to the mouth. One of the best things babies do at sixth months of age is smile in response to their parents' voices, and sometimes they laugh and chuckle. Babies at this stage of development also enjoy looking at themselves in a mirror or looking at other babies. Peek-a-boo is often a favorite game.
╞Chromosomes
The photograph above shows the 23 pairs of chromosomes that are obtained from a normal amniocentesis. The collection of chromosomes, arranged in this way, is called a karyotype. This particular individual will be a male because there is both an X and a Y chromosome. All males have an X and a Y chromosome, while all females have two X chromosomes. This means that all egg cells (ova) will have an X chromosome since that is all they can get from the mother. On the other hand, half of the sperm cells produced by a man will contain an X chromosome while the other half will contain a Y chromosome. The sex of a new individual, male or female, is determined by whether the ovum is fertilized by an X or a Y sperm cell. There are other things besides the sex of the developing fetus that can be learned from the karyotype. The most commonly seen abnormality is three copies of the 21st chromosome. This abnormality causes Down's syndrome, also known as trisomy 21. Other abnormalities including trisomy 13 and trisomy 18 can occasionally be seen. The numerous remaining possible genetic abnormalities are likely so severe that development would never get far enough along for an amniocentesis to be performed.
<Cirrhosis
The liver is perhaps the most robust of all the body's organs. As much as three-quarters of the liver can either be removed or destroyed, and the remaining liver cells will grow to replace the whole liver once again. It is possible, however, to damage the liver through repeated exposure to toxic chemicals. The most common example is alcohol abuse. Alcohol is a chemical that is toxic to the body in large doses. The liver detoxifies the alcohol and removes it, but not without damage to the liver itself. Heavy alcohol consumption over many years eventually leads to liver failure. This is called "cirrhosis." The illustration above shows a cirrhotic liver with a close-up of a small section. The other major cause of cirrhosis is chronic hepatitis, due to infection of the liver with one of the hepatitis viruses.
ûColon Cancer
Colon cancer is one the most common types of cancer in the U.S. Although there is no single cause for colon cancer, there are two factors that appear to play a large role. These factors are diet and inheritance. The picture above shows the colon along with a number of chromosomes to illustrate the fact that inheritance plays a role in the development of colon cancer. Diet, however, appears to be the biggest factor. Rates of digestive tract cancer vary widely in different part of the world. In China, cancer of the esophagus is quite common while this is disease is very uncommon in the U.S. In Japan, there is a high rate of stomach cancer, another disease that is rare in the U.S. In contrast, the most common digestive tract cancer in the U.S. by far is cancer of the colon. These findings implicate dietary differences as a cause of digestive tract cancers. Most doctors and scientists believe that it is the high fat, low fiber western diet that is to blame for the high incidence of colon cancer. Like other forms of cancer, the prognosis for colon cancer is relatively good if it is discovered early, before it has spread to other parts of the body.
ƒThe Colon
The colon consists of four main segments: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The appendix is a small, finger-like extension from the cecum, which is in turn part of the ascending colon. The primary role of the colon is to resorb the fluid from the watery mixture that is left over after the small intestine has completed absorbing all the useful nutrients.
πInside the Colon
The picture above shows the inside of the colon as taken with an endoscope. The walls of the colon contain three longitudinal (lengthwise) bands of muscle that create a purse string appearance. These periodic indentations in the wall of the colon are called "haustra." The haustra are clearly seen in the image above. Endoscopy of the colon is performed to allow direct visualization of the colon lining. If anything of concern is sighted, a biopsy will generally be obtained.
ñCrohn's Disease
Crohn's disease is an inflammatory disease that can affect any part of the digestive tract from the mouth to the anus. It is a serious problem that causes many symptoms including pain, fever, diarrhea, and weight loss. The most common site of involvement is the terminal ileum where the small intestine joins the large intestine. The inflammation generally becomes quite severe, sometimes even causing holes (fistulae) to develop in the walls of the intestine. Crohn's's disease tends to be patchy in its involvement of the intestine, with areas of disease interspersed with regions of normal intestine. Treatment for Crohn's disease is directed at relieving the inflammation. This is usually successful at controlling the disease. There is neither any known cause for the disease, nor any definite cure. Surgery to remove affected segments of the digestive tract is always a last resort because the disease tends to recur in other segments.
A related inflammatory bowel disease is Ulcerative colitis (UC). UC is different than Crohn's disease in a few important ways. It only affects the colon, sparing the remainder of the digestive system. It affects continuous segments of the colon so there is never interspersion of normal and diseased intestine. Only the inner lining becomes inflamed with UC, whereas the full thickness of the intestinal wall is affected with Crohn's disease. Treatment is about the same, however, with medicines directed at reducing the inflammation. Of special note, people with UC are at high risk of developing colon cancer, and they must be screened regularly. Sometimes, it is prudent to simply remove the colon to prevent colon cancer from occurring.
mCT Scan
Two new techniques have been developed over the last twenty years that have revolutionized the diagnosis of brain diseases. The first of these to be developed was computed (axial) tomography. This technique is popularly known as either CAT scanning or CT scanning. The first CT scanner came into operation in 1972 in London, England. During the exam, the patient lies with their head in a large device that has a doughnut like opening. The device is basically a sophisticated x-ray tube that is able to spin around the patient and take pictures of the head from every angle. In the most modern CT scanners, the x-ray tube itself doesn't even need to move. Instead, the x-ray beam is simply deflected so that it travels in a full circle around the patient. With either type of CT scanner, a powerful computer is then used to put all the data back together to form detailed images of the brain. Of note, CT scanning is quite general, and any other part of the body can also be scanned. CT scanning is particularly useful because it can be performed so rapidly. Only a few minutes are required to complete the examination.
¢Chest X-Ray
The picture above shows a standard x-ray of the chest. The heart is a relatively dense structure which shows up as a white shadow in the middle of the chest. In contrast, the lungs are filled with air. The air doesn't stop many of the x-rays from reaching the film behind the patient. The lungs thus show up as dark structures. Despite its simplicity, or perhaps because of it, the chest x-ray remains one of the most useful screening tests in medicine. The size of the heart is easily seen on the chest x-ray, a valuable piece of data which implies much about the function of the heart. Also, it is relatively easy to see whether there are any obvious problems with the lungs such as pneumonia. This condition is easy to diagnose because the affected parts of the lungs become more dense and show up as whiter on the x-ray. In serious cases of pneumonia, the alveoli tend to fill up with water and cellular debris. This may render them entirely white on the x-ray. When the alveoli fill up with water, it prevents the red blood cells from picking up oxygen and causes hypoxia. Hypoxia merely means low oxygen. This is the main problem for patients with pneumonia.
╧Defibrillator
When the pattern of the heart beat isn't normal, it is called an arrhythmia. Most arrhythmias produce strikingly abnormal EKG tracings. One interesting group of arrhythmias is caused by a block in the heart's normal conduction pathway. Fortunately, this does not stop the heart completely since there are always some cells below the level of the block that take over the role of initiating the heart beat. The new pacemaker cells tend to beat too slowly, however, so this isn't really a solution. Definitive treatment for a heart block arrhythmia thus requires placement of a battery powered pacemaker. The pacemaker can then be programmed to initiate the heart beat at any desired rate.
The most severe arrhythmia is ventricular fibrillation. A heart in ventricular fibrillation just quivers, and it is unable to pump blood. Effective treatment depends on shocking the heart to get all the muscle cells to begin contracting again in an orderly fashion. The machine used to deliver the shock is called a defibrillator. The paddles from a defibrillator are shown in the picture above. The power of the shock is quite great, and it is very important that all the bystanders stay clear when the defibrillator is used.
╧Mental Health
The brain is the most complex organ, and it is the focus of much medical research. One of the many fields of research involving the brain is mental illness. Serious mental illnesses such as depression and schizophrenia are remarkably common disorders of the brain. Depression affects approximately 10 - 15% of people at some time during their lives. Schizophrenia is estimated to affect just under 1% of the world's population. These numbers make for quite a few cases. There are as many as 1.5 million U.S. citizens with schizophrenia at any one time.
Schizophrenia usually begins between the ages of 15 and 25. The symptoms often appear when a young adult leaves home for the first time to live on his or her own. The illness is equally prevalent in males and females. It is a common misconception that schizophrenia is the same thing as multiple personality disorder, but the ailments are actually quite unrelated. Multiple personalities, as in the story of Dr. Jekyll and Mr. Hyde, is an extremely rare disorder. Schizophrenia is a psychotic illness characterized by profound disturbances in thought and behavior. Patients frequently experience both delusions and hallucinations. Delusions are false ideas that have no reasonable basis in fact (for example, I am invisible). Hallucinations are sensory experiences that occur without any external stimulus. Schizophrenics often feel as if they are being controlled by other forces, such as someone on the television set. The causes of schizophrenia remain incompletely understood. Inheritance definitely plays a significant role. For instance, the identical twin of a patient with schizophrenia has a 50% chance of also having the disease, even if they were raised apart.
Dialysis
The primary functions of the kidneys are to maintain the fluid and salt balance in the blood, and to remove waste products. These jobs are quite essential. If the kidneys fail for any reason, wastes start to accumulate, and the body becomes overloaded with fluid. Fortunately, this problem can be treated with an artificial kidney machine that can be hooked up to the patient when needed. This process is called "dialysis." Usually, patients will undergo a three-hour hemodialysis session about three times a week. The picture above shows a man leisurely reading while receiving dialysis. Kidney transplants are another method for treating people whose kidneys have stopped working. Diabetes is the most common cause of kidney failure that ultimately requires treatment with dialysis.
\DNA Replication
The basic structure of DNA is the double helix. The double helix is formed from two individual strands that complement each other perfectly. In fact there are only four main building blocks, referred to as A, T, G, and C. An A block always pairs with a T block and a G block always pairs with a C block. This remarkably simple structure makes it easy to see how DNA is replicated. An enzyme called DNA polymerase merely needs to separate the two strands of the parent double helix, and then use each strand as a template for a new daughter double helix. Although all the information is contained in each single strand, the double helix does offer redundancy that makes it vastly easier to repair errors when they occur.
DNA can also be copied to make a related molecule called RNA. RNA is the messenger molecule that carries the DNA information out of the nucleus and into the cell for action. The process of copying DNA into RNA is called transcription. The RNA is then used to direct the synthesis of proteins. Unlike DNA and RNA which only use four unique building blocks (bases), proteins are made using 20 unique building blocks called amino acids. To specify the 20 unique amino acids using only the four bases available to either DNA or RNA, simple math tells us that it must require a group of three bases (a triplet). This provides for 64 (four cubed) different triplets that can be made from the four bases. There is a code that states which of the 20 amino acids goes with each of the 64 different RNA triplets. The process of using the RNA to direct the synthesis of proteins is called translation.
ΦDNA
DNA is the molecule which contains all the information for life. It can be thought of as a blueprint or an instruction manual for how everything necessary for life must be done. At the smallest level, DNA is organized into a double helix as shown in the illustration above. The DNA helix is then repeatedly coiled to allow more of it to fit into a compact space. In humans, all the DNA is packaged into 46 separate molecules called "chromosomes." The chromosomes each contain thousands of genes, with each gene specifying how to make a particular protein necessary for cellular function. Scientists have long thought that the holy grail for understanding human life lies in knowing the entire sequence of human DNA. For this reason, the National Institutes of Health are funding the human genome project. The mission of the human genome project is to sequence all the DNA contained within a human cell. This is a project of enormous magnitude that will likely take many years to complete.
πThe Eardrum
The photograph above shows an eardrum (tympanic membrane) as seen through an otoscope. The dominant feature of the picture is the appearance of the middle ear bones (ossicles) that can be seen through the eardrum. Doctors are looking to see this normal anatomy when they examine a person's ear. The eardrum is a taut, thin membrane that vibrates in response to sound waves. Sound waves of different frequencies, like a bass drum or a violin, cause the eardrum to vibrate at different speeds. In order for the eardrum to vibrate freely, and thus work properly, the pressure needs to be the same on both sides of the eardrum. This explains why hearing decreases when the ears are clogged or when a person has a middle ear infection. Pressure equalization between the middle ear and the outside is achieved through the eustachian tube which connects the middle ear to the throat. It is unwise to ever place anything sharp into the ear that might damage the eardrum. However, the eardrum usually heals without problems if it is punctured. In fact, a common treatment for chronic middle ear infection in children is to place tubes through the eardrums that allow fluid to drain out from the middle ear. These tubes are called myringotomy tubes.
EThe Inner Ear
The inner ear consists of the cochlea and the semicircular canals. The cochlea serves to permit hearing while the semicircular canals are necessary for balance. The cochlea is a small, spiral shaped structure containing fluid and special hairs which serve as sound sensors. The photograph above shows a picture of some of these hair cells within the cochlea. Sound waves entering the ear set up a chain of vibrations, starting with the eardrum. The vibrations are then transferred via the middle ear bones (ossicles) to the cochlea. One of these bones (the stapes) moves up and down in the oval window causing fluid waves in the cochlea that are dependent on both the frequency of the sound, and its amplitude (volume). The response of the hair cells to these waves is dependent on their location within the cochlea. The cochlea is designed such that the hair cells right near the oval window move in response to high frequency sounds while those furthest from the oval window move in response to low frequency sounds. There is a very smooth gradient between the two extremes. The brain is thus able to tell what frequency a sound is by which of the hair cells in the cochlea are moving and sending out sound signals.
As noted above, the semicircular canals are necessary for balance. There are three of these canal that are positioned at right angles to one another. Like the cochlea, they contain fluid and specialized hair cells. They are different, however, because they contain small crystals that move freely in the fluid when the head moves. These crystals brush against the hair cells to indicate that the head has changed in position. If one spins around and around, the fluid and the crystals continue to move even after the head has stopped moving. This explains why a person becomes dizzy and may fall down from too much spinning.
üImaging with Sound
Ultrasound is an important diagnostic technique that has many uses in medicine. Ultrasound scanning is accomplished with a hand held device (transducer) that can emit very high frequency sound waves, and then "listen" for the return of the echoes. Different tissues vary greatly in their tendency to echo back the sound waves (echogenicity). These differences in echogenicity are used to create detailed images of the body. The sound waves emitted by the ultrasound machine penetrate through fluid very well, but they cannot penetrate through either bone or air. This is why the transducer must be placed right onto the patient's body with jelly used to exclude all of the air between the transducer and the skin. When ultrasound of the heart is done, it is called echocardiography.
Echocardiography is an extremely common test. It is used to study both the structure of the heart, and how well the heart is working. The main structural components of the heart that can be seen with echocardiography are: the four heart chambers, the four valves, and the walls which separate the right and left sides. In looking at the four heart chambers (two atria and two ventricles), the most important thing is their size. There is a definite normal range, above which the heart is said to be enlarged. An enlarged heart is typically a sign that it has begun to weaken and fail. The heart may be enlarged for many reasons. One of these reasons is a problem with one of the four valves. A valve can be either abnormally leaky (regurgitant), or abnormally narrowed (stenotic). Another possible cause of an enlarged heart is a hole in one of the walls that separate the right and left sides. There may be a hole between the two atria and/or a hole between the two ventricles. This "hole in the heart" condition is a very common birth defect, affecting about one in every 400 babies born. Typically the hole heals by itself, but sometimes surgery is required. The heart may also be enlarged because of an infection or a chemical which has damaged the heart muscle. Alcohol is one of the chemicals known to be toxic to the heart muscle if it is consumed in great excess.
Ectopic Pregnancy
Rarely, an embryo will accidently implant in a fallopian tube rather than in the uterus as it should. This is called an ectopic pregnancy. Unfortunately, the fallopian tube cannot expand and nourish the embryo as the uterus can, and there is no way for the embryo to develop to term. Usually, a woman with an ectopic pregnancy winds up in an emergency room complaining of severe lower abdominal pain and vaginal bleeding. A test is done first to determine if she is pregnant. If she is, then there is a reasonably high chance that she has an ectopic pregnancy. An ultrasound examination will usually be done next to help determine whether there is in fact an ectopic pregnancy. An ectopic pregnancy is an emergency that needs to be treated surgically. It is important to remove the developing embryo before the fallopian tube bursts. The primary risk factor for ectopic pregnancies is a history of fallopian tube infection which often scars the tubes. This makes it more likely that a fertilized ovum will fail to reach the uterus.
└EKG
As it beats, the heart generates small electrical currents. A recording of this electrical activity is called an "EKG" (electrocardiograph). The terms EKG and ECG mean the same thing. EKG comes from the German language while ECG comes from English. A standard EKG is obtained by placing 12 small electrodes on the patient's body in a specific pattern. The EKG machine is then turned on, and the recording is made in just a few moments. The test is entirely painless.
The picture above shows three heart beats taken from a normal EKG. Each of these beats can be divided into three main parts. The first part is the small P wave which represents the atrial contraction. The second part is the tall QRS spike which represents the ventricular contraction. The third part is the large T wave which represents the relaxation of the ventricles. By analyzing the exact pattern of the EKG, doctors can learn a great deal about how the heart is working.
rThe Zygote
As soon as fertilization takes place, the new cell is called a "zygote." Things immediately begin to happen within the zygote. First, the genetic material (DNA) is released from the head of the sperm. These 23 chromosomes are then able to join up with the 23 chromosomes of the ovum to form a full set of 46 chromosomes. The zygote thus contains all the genetic material for the new individual. Measuring only about four-thousandths of an inch (0.1 millimeter) in diameter, the zygote sets about the business of starting to divide while it continues its lazy journey down the fallopian tube toward the waiting uterus.
Twenty-One Day Embryo
After three weeks, the disk of cells becomes more elongated. The head of the embryo forms at one end while the lower part of the spine forms at the other. A group of cells along the embryo's developing back forms the notochord which goes on to form the spine itself. At this point in development, the embryo has a recognizable left and right side. The notochord next moves into the body of cells, away from the surface. The edges created curl around and fuse to form the neural tube itself. The neural tube goes on to form the brain and spinal cord. It is important to realize that these critical steps for forming the spine, spinal cord, and brain all take place scarcely after a women would realize she has missed her period. Prenatal care should really begin as soon as a couple even begins trying to conceive a baby. Sometimes, the neural tube fails to fuse properly. This may leave an opening in the brain or spinal cord called a neural tube defect. Recent studies have suggested that giving all women of child bearing age extra folic acid, a simple dietary supplement, may significantly reduce the frequency of neural tube defects. Of course, the folic acid needs to be given before pregnancy since the critical steps in neural tube formation occur so soon after fertilization.
GTwenty-Eight Day Embryo
During the fourth week after fertilization, most of the organs begin to be formed. The back grows more rapidly than the front, creating a C-shape to the embryo. Tissue buds develop that go on to form the lungs, the liver, the gallbladder, and the pancreas. The heart begins its development as a straight tube. Rudimentary ear and eye pits are seen. The neural tube also continues to develop as it extends more toward the head where the brain will develop. This period is called "organogenesis," since so many organs begin to be formed. It is at this point in development that the embryo is at greatest risk for developing birth defects from external toxins such as drugs or radiation. It is worth stressing that this critical period is quite early in pregnancy, soon after most women will have discovered that they are pregnant.
)Six-Week Embryo
By the sixth week after fertilization, the embryo begins to look recognizably human. The face begins to form along with the eyes and the ears. The limbs also start to develop rapidly and become jointed. The tail disappears. The embryo still has a long way to go, but it is well on its way.
bSeven-Day Embryo
On about the sixth day past fertilization, the sphere of cells implants into the uterine lining. At this point, the developing embryo begins to obtain its nourishment from the mother. The outer layer of cells go on to form the placenta at the point of attachment to the uterus. The embryonic cells, all initially in a ball, next begin to separate to form a flat disk with a fluid cavity on either side. The embryo at this stage is called a "blastula." The flat disk contains the cells that will ultimately go on to form all the baby's tissues. The amniotic sac develops around the embryo as it grows.
σEight-Cell Embryo
Nearly as soon as the zygote forms, it begins to divide again and again to form more cells. Initially, all of this cell division (mitosis) takes place without any change in the size of the developing embryo. The first cell division takes place about 24 hours after fertilization. The picture above shows the embryo at an eight-cell stage, about 48 hours or so after fertilization. The embryo is on its way to becoming a ball of cells, all exactly the same, called a "morula." Identical twins are formed when the cells of the morula split into more than one ball. This can sometimes occur during the frenzy to keep dividing. The separate and identical balls of cells can then each go on to form new and genetically identical people.
─Inside the Duodenum
The photograph above shows the inside of a normal duodenum as seen through an endoscope. An endoscope is a flexible tube with both a light and a camera lens at its end. Doctors often use the endoscope to examine the digestive tract when a patient develops vomiting or diarrhea that doesn't resolve as expected. Tiny surgical tools can also be manipulated through the endoscope, allowing treatment of a wide variety of digestive system disorders.
⌠Inside the Stomach
The picture above shows the inside of the stomach as seen through an endoscope. The endoscope is a flexible tube that allows doctors to look inside the body through a fiber optic lens at the tube's end. By using an endoscope, a doctor is able to look directly at the inside of the digestive tract to make a diagnosis, and possibly even to treat the problem. Some of the many problems that can readily be seen with an endoscope include tumors, ulcers, and dilated blood vessels (varices). The endoscope is controlled with hand-held dials that direct the tip of the endoscope so that it can be steered into the stomach and beyond. In the picture above, note the thick folds in the muscular stomach walls. This is the appearance of a normal stomach.
zHormones
Hormones are chemicals that are manufactured by glands within the body and then released into the bloodstream. From there, the hormones travel to all parts of the body where they influence a wide number of body processes. The glands which collectively make these hormones comprise the endocrine system. This system includes the adrenal glands, the gonads (testes or ovaries), the pancreas, the parathyroid glands, the thyroid gland, and the pituitary gland. In pregnant women, the placenta also functions as part of the endocrine system by making hormones that are released into the bloodstream. Hormones are also made by other organs including the kidneys and the heart, though these organs are not commonly thought of as part of the endocrine system. The process of releasing hormones into the bloodstream is called "exocytosis." This process is shown in the illustration above.
HFetal Monitor
The birth process is quite stressful for both the mother and baby. Although most births are uncomplicated, there is always the potential for something to go wrong. For this reason, it is commonplace to use a fetal monitor to assess the status of the baby throughout the labor and delivery. The fetal monitor typically uses a small probe which is attached to the baby's head through the cervix. With this probe, it is possible to determine continuously the baby's heart rate. A belt is usually placed on the mother as well to monitor the rate and strength of her contractions.
°Female Reproductive System
The female reproductive system consists of the ovaries, the fallopian tubes, the uterus, and the vagina. These structures are all shown in the illustration above, with the ovaries and uterus highlighted in orange. The eggs are all contained within the ovaries. Each month, there is a cycle of hormones which causes one of the woman's eggs to mature and burst out from the ovary. The egg cell, or ovum, is then picked up by one of the fallopian tubes which gently brushes the ovum down toward the uterus. The uterus has already readied itself for the ovum by increasing the thickness of its lining. If the ovum is fertilized by a sperm, then the ovum will implant in the uterine lining and develop into a new baby. If it is not fertilized, it will wither away, and the uterine lining will be discarded in a process known as menstruation. The whole process repeats itself each month throughout a woman's reproductive years. Interestingly, a women is born with all the egg cells that she will ever have. During childhood, the egg cells lie dormant, awaiting puberty when they will begin to mature and be released. Women have many thousands of eggs, but only one, or at most a few, mature each month. Women thus have many more egg cells than can ever be released.
Ten-Week Fetus
The developing child is referred to as a "fetus" rather than an "embryo" after the eighth week. The photograph above shows a fetus at approximately the tenth week of development. At this point, the fetus is about two inches (five centimeters) in length. Blood cells are being produced by the liver and spleen, and the now-completed fetal heart is already pumping these red blood cells around the body. At this point, all the organs have formed. Further development mostly involves maturation of these rudimentary organs.
ìFour-Month Fetus
This remarkable photograph shows a fetus after four months of development. The face is quite well developed as are the hands. Sometimes, fetuses of this age can even be observed sucking their thumb. This photograph was obtained by using a special fiber optic camera that was placed inside the uterus. Even the detail in an ultrasound picture pales in comparison to that seen in this image.
"Eight-Month Fetus
By eight months after conception, fetal development is nearly complete. The baby can be expected to do satisfactorily if it is born at this stage, though there could be minor complications. Among the last things to develop to full maturity are the lungs. The illustration above shows the fetus with its head down, firmly seated against the cervix. This is the optimal position for the fetus to be in for a vaginal delivery. Also evident in the illustration is the placenta, which serves as the connection between the fetus and the mother.
╥The Flu Virus
There are three main types of influenza viruses, named type A, B, and C. The schematic illustration at left shows a single influenza virus. Among the most notable features are the little spikes (shown in white) that stick out from the viral surface. The exact nature of the spikes (glycoproteins) determines the type of the influenza virus. Immunity to influenza occurs when the immune system makes antibodies that bind to these glycoprotein surface spikes. Unfortunately, the type A and, to a lesser extent, type B influenza viruses are unstable, with new versions appearing every year. When a new version appears, the antibodies still circulating in the body from the last bout of influenza will be less effective at eliminating the virus, and the person may get ill once again. Occasionally, an influenza virus will appear that is so radically new that virtually no one is immune to it. When this occurs, the result is a worldwide flu outbreak called a "pandemic."
╤Upper GI Series
The upper GI series is a common method for looking at the digestive tract. The digestive tract is also called the gastrointestinal (GI) tract, hence the name "upper GI series." This technique has been used for many years. It has the advantages of being cheaper and less invasive than endoscopy. An upper GI series involves the patient drinking a small amount of a barium solution while x-rays of the esophagus, stomach, and small intestine are taken from many angles. The barium solution outlines the inside of the digestive system and enables excellent diagnostic pictures to be taken. For most patients, the worst part of this test is the taste of the barium, which is usually described as seeming like chalk.
.Gallstones
A common medical problem is the formation of gallstones within the gallbladder. These stones are of three main types: cholesterol stones, pigment stones, and mixed stones. The picture above shows examples of the different stone types. The majority of stones are of either the cholesterol type or the mixed type. Four times as many women as men are affected by gallstones. Most gallstones are silent and cause no problems. Sometimes, however, a stone can become lodged in the neck of the gallbladder or in the cystic duct, leading to great pain and infection of the gallbladder. Removal of the gallbladder is the most common treatment for this problem. Removing the gallbladder does not seem to have any harmful effect on digestion or any other process. In recent years, a method for removing the gallbladder without major surgery has come into widespread favor. This procedure is called "laparoscopic cholecystectomy." Patients undergoing this procedure are generally released from the hospital after only one day, and they can return to work within a week.
&Keeping the Beat
The heart beat is usually divided into two main phases called "diastole" and "systole." During the first phase (diastole), the heart relaxes and fills with blood. During the second phase (systole), the heart contracts and pumps out the blood. The heart typically spends about 2/3 of its time in diastole and 1/3 of its time in systole. Keeping this activity well timed is the job of the heart's conduction system.
The signal to begin a contraction starts in a small region at the top of the right atrium called the "sinoatrial (SA) node." From this point, the contraction spreads over the two atria like a wave. The atrial contraction pumps the blood down into the ventricles. Next, the signal to contract reaches a small region of the heart called the "atrioventricular (AV) node." As its name implies, the AV node sits right between the atria and the ventricles. The AV node is smart, and it delays the signal just long enough to allow the atria to finish contracting. From here, the signal to contract travels down special fibers that connect to the bottom of the heart. This causes the ventricles to contract from the bottom to the top, and ensures that the blood is pumped up and out, into the lungs and the body. At the end of the cycle, the ventricles relax and the whole process begins again.
▀Coronary Arteries
Although the heart is constantly pumping blood, it does not actually get any oxygen from the blood which travels through its chambers. Instead, the heart receives all of its oxygen from the arteries which encircle it. These blood vessels are known as the "coronary arteries." The word "coronary" comes from the Latin word "corona," which means crown. There is a right and a left main coronary artery. These all-important arteries exit from the aorta just above its attachment to the heart. The left main coronary artery is actually quite short. Soon after exiting from the aorta, it divides into two large branches called the "circumflex" and the "left anterior descending" arteries. Under normal circumstances, the coronary arteries have significant reserve capacity, and they can easily meet the oxygen demands of the heart muscle. Problems with supplying the heart muscle with oxygen arise only when the coronary arteries become significantly narrowed due to atherosclerosis.
┴Heart Attack
People with coronary artery disease are at high risk for having a heart attack. A heart attack occurs when the blood supply to a part of the heart is suddenly cut off, and the affected heart muscle dies. The usual cause of a heart attack is the formation of a blood clot at the site of an atherosclerotic plaque. The clot completely blocks the artery, cutting off blood flow beyond it. The medical term for a heart attack is myocardial infarction.
Heart attacks are the number one cause of death in western societies. The risk factors for having a heart attack are well known. These risk factors include a diet high in fat and cholesterol, smoking, obesity, physical inactivity, high blood pressure, diabetes, and a family history of heart attacks. Fortunately, most of these risk factors are related to lifestyle. It is thus possible for a person to lower their risk of a heart attack if they choose to. Of note, the incidence of heart attacks is four times lower in Japan than it is United States. This is because the major risk factors are much less common in that country.
The diagnosis of a heart attack is based mostly on the patient's symptoms. Typically a patient having a heart attack experiences severe chest pain, sweating, nausea, and anxiety. The diagnosis is confirmed by an EKG along with blood tests. If a patient arrives at the hospital soon after their symptoms began, they will generally be treated with a medicine (thrombolytic) that works by dissolving blood clots. This treatment is often successful at reopening blocked arteries, and limiting the damage done to the heart. The severity of a heart attack is determined by how much of the heart dies. If too large a part of the heart is affected, the remaining heart muscle is unable to continue pumping the blood. Approximately one third of heart attacks are fatal. Advances in medical care over the past 30 years have greatly improved the outlook for patients that survive a heart attack.
ⁿOpen Heart Surgery
Open heart surgery first became possible in the mid-1950's when the heart-lung machine was introduced. Once connected, this machine serves to oxygenate and pump blood to the brain and other tissues throughout the body. This enables the surgeons to stop the heart, open it up, and make needed repairs, all the while taking as much time as is needed.
The most common open heart operation in the Western world is coronary artery bypass grafting. Another common heart operation is valve replacement. The most aggressive open heart operation is heart transplantation. The first successful heart transplant program began at Stanford University in 1969. One of the biggest problems with organ transplantation is rejection of the transplant by the patient's immune system. In the last ten years, however, there has been significant advancement in the medicines that are used to prevent rejection. Approximately 85% of patients receiving a heart transplant can now expect to live for at least a year after the surgery.
₧Compact Bone
Bones are formed of a thin outer surface layer (periosteum) containing blood vessels and nerves, an outer shell made of dense compact bone, and a core composed of spongy bone. The dense outer shell is made of orderly columns of bone cells that are mineralized with calcium phosphate to make them resilient and strong. These bone columns are called Haversian canals. The photograph above shows a number of Haversian canals in cross section.
Bone growth and shape is the result of a delicate balance between calcium deposit and resorption. Osteoblasts are bone cells that work to deposit new calcium phosphate taken from the blood, while osteoclasts work to resorb calcium phosphate and return it to the blood. This balance is controlled by many different hormones (growth hormone, sex hormones, adrenal hormones, thyroid hormone, and parathyroid hormone). It is very important that the amount of calcium in the blood be strictly regulated so that muscles and nerves in the body function properly. The growth and shape of bones is also influenced by the mechanical stresses placed on them. This ensures that the bones that support the weight of the body are very strong.
╤The Auditory Pathway
Hearing begins with the pinna channeling sound waves into the ear canal as shown in the illustration above. These sound waves cause the eardrum to vibrate. The middle ear contains three delicate bones (ossicles) which are attached to the eardrum on one side and the cochlea on the other. When the eardrum vibrates, the ossicles move with it and transfer the vibrations to the fluid within the cochlea. The cochlea is a spiral, seashell-shaped structure containing fluid and many specialized hairs that move in response to fluid waves. Movement of the hair cells stimulates nerve fibers to send a signal to the brain. The louder the sound is that enters the ear, the more the eardrum moves, and the stronger the waves are that are created in the fluid within the cochlea. In turn, the hair cells in the cochlea move more, and a stronger signal is sent to the brain along the eighth cranial nerve. Ultimately, the brain will interpret the strong signal as a loud sound.
Hemoglobin
Red blood cells are completely filled with hemoglobin, a special molecule designed to carry around oxygen and carbon dioxide. Amazingly, there are about 350 million hemoglobin molecules in each and every red blood cell. The hemoglobin molecule consists of four basic units (globin chains), as shown in the picture above. The four chains always consist of two matching pairs. In the adult human, there are two identical alpha chains, and two identical beta chains. Each of the four chains has a single iron atom in its center. The four iron atoms enable the hemoglobin molecule to bind with four oxygen molecules. Oxyhemoglobin is formed when oxygen molecules combine with hemoglobin. Oxyhemoglobin is bright red, and it gives blood its usual color. When the oxygen molecules are released into the tissues, however, hemoglobin turns greenish. This explains why venous, deoxygenated blood appears darker than arterial, oxygenated blood. This is easily observed in the veins that are just beneath the skin surface.
HLiver Cell
The illustration above shows a single liver cell, commonly referred to as a hepatocyte. Its general structure is the same as other cells. It is surrounded by a membrane that keeps the cell intact, while excluding undesirable molecules from freely entering the cell. Cell membranes have specific channels in them that are used to regulate the passage of molecules into and out of the cell. Inside the cell there are numerous cellular "organs" called organelles. These structures perform specific functions that are needed by the cell, such as the synthesis of new cell components. One of the most important organelles is the mitochondria which are shown in purple above. The mitochondria are responsible for producing energy for the cell. At the middle of the cell is the nucleus. The nucleus contains the DNA. The DNA serves as the instruction manual for how to carry out all the cellular functions. Interestingly, all the different cells in the body have the same DNA. Somehow, the different types of cells all know enough to read the pages of the manual that are specific to them.
ΦArtificial Hip
The movable joints of the body have fibrous capsules that are lined with a membrane (synovium) that secretes a thick lubricating fluid. The moveable joints also have cartilage at the ends of the bones which acts as a cushion between the bones. These joints are referred to as synovial joints. Osteoarthritis is a joint disease caused either by damage to the cartilage within the synovial joints, or by the formation of bony spurs. Osteoarthritis is the same thing as degenerative arthritis. Nearly all people over the age of 65 have osteoarthritis to a greater or lesser extent so it can reasonably be thought of as part of the aging process. In some people, however, osteoarthritis is quite severe, causing great pain and disability. The hips, knees, and spine are particularly prone to osteoarthritis as is the joint at the base of the thumb.
When severe osteoarthritis causes joint destruction, it is often possible to offer joint replacement as a method of treatment. Hip replacement is the most common of these operations. In this operation, the top of the femur is removed along with the normal hip socket. A metal shaft with a ball at its top is placed into the remaining part of the femur. A cup made of metal or plastic is placed into the pelvis. This operation is usually very successful, often restoring patients to a normal level of activity. Other joints including the knee and shoulder are sometimes replaced, but the results are generally not as reliable as with hip replacements.
▄AIDS Virus
Every time period appears to have had its own scourges, and our time is no different. Today the health community and the public are confronted with the AIDS problem. AIDS stands for acquired immuno-deficiency syndrome. AIDS is a clinical condition in which the body repeatedly succumbs to opportunistic infections because of a weakened immune system. AIDS is caused by the human immunodeficiency virus (HIV). Thus far, it appears that all individuals who contract HIV will eventually develop AIDS, a uniformly fatal disease. There are medications that slow the course of the disease, but no definite cure is on the horizon. One would think that the answer to the problem lies in an effective vaccine, but scientists have thus far been unable to make such a vaccine. HIV is an unusual virus in that it attacks the very cells in the immune system whose normal role would be to kill the virus. No such virus had ever previously been isolated. Fortunately, the routes of HIV transmission are well understood, and show no signs of changing. At present, it is only possible to contract HIV by exposure to either blood or genital tract secretions from an infected person. Unprotected sex with infected partners and needle sharing remain the most common routes of transmission by far. Exposure to HIV through blood transfusions was largely eliminated in the mid 1980's when screening tests for HIV became available. The picture above shows a virus budding out from an HIV infected lymphocyte.
UInsulin
Insulin is an important hormone that is made by the pancreas. After a meal is eaten, insulin is released. The insulin serves as a messenger to all the cells of the body that they should take up glucose (sugar) from the blood and store it. Diabetes is a disease generally caused by an underproduction of insulin. Without this signal, the cells fail to take up the glucose, and blood sugar levels can rise to very high levels. When the blood sugar level reaches a high enough point, glucose begins to spill into the urine. This is why doctors initially check the urine to test for diabetes.
ΩThe Small Intestine
The illustration above depicts a short segment of small intestine. The small intestine is a long tube (about 21 feet, or 6.5 meters) whose purpose is to absorb food. The inner layer of the small intestine (mucosa) is very well suited for this job. It is organized into innumerable little, finger-like projections called "villi." The mucosal cells which line the villi are in turn covered with even smaller finger-like projections called "microvilli." The villi and microvilli greatly increase the surface area with which to absorb food. The middle layer of the small intestinal wall contains two layers of smooth muscle. These smooth muscle layers contract in a rhythmic manner (peristalsis) to keep food moving down the digestive tract.
Irritable Bowel
Irritable bowel syndrome is a condition in which people experience intermittent abdominal pain and irregular bowel habits without any other demonstrable evidence of disease. People with irritable bowel syndrome have no other symptoms, and they do not become either malnourished or lose weight. The cause of this syndrome is not well understood, but is assumed to be related to some disturbance of the smooth muscle within the walls of the large intestine. Surprisingly, it is the most common intestinal disorder, accounting for more than half of all the patients seen by doctors who specialize in digestive system problems (gastroenterologists). Prior to making the diagnosis of irritable bowel syndrome, it is still necessary to run tests to exclude other more treatable illnesses.
±Edward Jenner
The principle of vaccination is one of the landmark discoveries in the history of medicine. This triumph is credited to Edward Jenner. In his time, the great scourge was smallpox, a highly infectious and lethal viral infection. Its impact on the population at that time dwarfs the impact that AIDS, the worst scourge of our time, is having today. Edward Jenner made the astute observation that the milkmaids of that day rarely ever developed smallpox. He reasoned that something about their tendency to contract a similar illness called cowpox might be involved. He hypothesized that these milkmaids were resistant to smallpox because they had already contracted a similar illness. In 1796, Edward Jenner tested this hypothesis by inoculating his eight year old son with material obtained from a cowpox lesion. Six weeks later, his son proved resistant when he was challenged with material from a smallpox lesion. The principle of immunization was thus established. This is an epic story indeed when you realize that Edward Jenner's young son would likely have died if Edward was wrong about his hypothesis. As an interesting footnote, the elimination of the smallpox virus ranks as one of the most significant successes of the World Health Organization (WHO). In 1967 the WHO mounted a campaign to eliminate small pox from the earth which culminated in 1977 when the last known case was recorded in Somalia. Only research strains of the smallpox virus remain, located in a few laboratories in the world.
Cleaning the Blood
The kidneys receive their blood supply directly from the aorta through the renal arteries. These arteries branch again and again within the kidneys to form small capillary tufts called "glomeruli." Each kidney contains about one million glomeruli which together serve as the filter for cleaning the blood. Blood cells and big molecules are kept within the glomeruli, but water and small molecules all pass through their walls. In fact, about 140 liters of fluid pass out of the glomeruli each day. All this fluid passes into the renal tubules where 99% of it is reabsorbed back into the blood. At the end of the tubules, however, the waste products, excess salt, and some of the water remain unabsorbed. These things form the urine which drains down the ureters and into the bladder.
Kidney Stone
There are a number of different types of kidney stones. The most common type, as shown in the picture above, is made of calcium salts. These stones are extremely hard, and they often have sharp edges. There is usually no definite cause for the formation of these stones, although diet and fluid intake certainly play a role. Less commonly, kidney stones form because of a kidney infection or some definite, treatable metabolic disorder. It is easy to see from the picture above why passing kidney stones causes such incredible pain.
VShock Waves
Sometimes, kidney stones form which are simply too large to pass. In the past, doctors used to perform surgery to remove the stones. In recent years, however, doctors have begun using a machine called a "lithotriptor" to treat large kidney stones. This treatment is non-invasive and relatively simple. As shown in the picture above, the patient sits in a bath of warm water during the procedure. The lithotriptor then emits high energy sound waves which are focused on the kidney stones. The sound waves pulverize the stones into small fragments that can then be passed through the urine.
&The Chemical Factory
The liver is a remarkably complex organ which serves as the chemical factory for the body. There is a very wide range of functions that are performed by the liver. One of these functions is to produce important proteins for the blood. Some of these proteins play roles in the immune system (complement factors), some in the blood clotting pathway (coagulation factors), and some in the regulation of intravascular blood volume (albumin). Another function of the liver is to help regulate blood sugar levels by storing glycogen when glucose is plentiful, and releasing it when it is needed. The liver also regulates the levels of many key molecules, such as amino acids.
Perhaps the most important role of the liver is to detoxify and remove many poisonous substances from the blood. The liver does this by absorbing the toxins from the blood, altering their structure to make them water-soluble, and excreting them into the bile. The bile is then emptied into the small intestine, and the now harmless toxins are eventually eliminated with the feces.
╡Receptors
Neurotransmitters are the messengers for nerve communication across synapses. However, there are many different types of chemicals that serve as neurotransmitters. How do the receiving cells distinguish all these signals? They do this by having very specific receptors. Each receptor is like a lock that can only be activated by a particular key, as in the correct neurotransmitter. The illustration above shows a neurotransmitter molecule bound within a receptor. Most drugs and toxins that affect the nervous system work by modifying the interaction of neurotransmitters and their receptors.
One of the most important neurotransmitters is acetylcholine (ACh) which is released by the neurons that stimulate skeletal muscles. Receptors on the muscle fibers recognize ACh as the signal to contract. Many animals, such as venomous snakes and puffer fishes, produce toxins that cause paralysis by blocking the ACh receptors. There is also a disease called Myasthenia Gravis that involves the ACh receptors. Patients with myasthenia gravis produce antibodies that bind to the ACh receptors and prevent them from receiving the normal signals to contract. Myasthenia patients thus suffer from profound weakness since their muscles don't contract when they are supposed to. Treatment involves administration of a medicine which causes the nerve terminals to release more acetylcholine than normal. Myasthenia Gravis is an example of an autoimmune disease. Autoimmune diseases result from a disorder of the immune system in which antibodies are made that react with normal parts of the body. Under normal circumstances, antibodies are only made to react with foreign molecules that are invading the body.
ELung Cancer
In the U.S., lung cancer has been the leading cause of cancer deaths in men for many years, and only recently has it achieved this same dubious status in women. Cigarette smoking is the main cause of lung cancer. The risk for developing lung cancer is directly related to the number of cigarettes smoked per day, and the length of time that a person has smoked. Doctors commonly use the term pack years, which is the number of cigarette packs smoked per day times the number of years that the person has smoked. The steady rise in the number of women developing lung cancer can be seen to correlate with an equal rise in the use of tobacco by women in the 20th century.
The photograph above shows a segment of the lung. Note how the cancer cells, shown in green, appear to be invading through the normal healthy respiratory lining, shown in yellow. This is a general property of malignant cancer cells. They tend to be disorganized, relatively non-functional cells, that lose regard for traditional boundaries and multiply out of control. They also have the ability to spread to distant sites, a process called metastasis. Lung cancer usually does not cause symptoms until late in the course of the disease. The first symptom is most commonly a worsening cough. Some people, however, are fortunate to have a lung cancer noted on a routine chest x-ray, early in the course of the disease. In these cases, the prognosis can be very good for long term cure. Available treatments include surgery to remove cancerous tissue, radiation therapy to kill cancer cells, and anti-cancer medicines.
"The Respiratory Tree
The structure of the lungs can be likened to a branching tree. Starting with the trachea (windpipe), the respiratory tree branches initially to form two main bronchi (airways) that enter the right and left lungs. The main bronchi then branch again and again, first forming smaller bronchi and then even smaller bronchioles. At the end of the smallest bronchioles, there are tiny, grape-like air sacs called "alveoli." It is in the alveoli that oxygen comes into contact with the red blood cells that will carry it to all parts of the body.
ºBack Pain
Neck and back pain are very common ailments. Most commonly, this pain results from strain of the muscles which support the spine. This type of pain is best treated with rest and heating pads. Occasionally, however, there is damage to the spine itself. Arthritis is the most frequent cause of spine problems. One of the ways arthritis can cause pain is by narrowing the small openings through which the spinal nerves exit from the spine. This causes pain by directly putting pressure on the spinal nerves.
Another cause of back pain is damage to one of the intervertebral disks. A ruptured disk occurs when severe pressure forces the jellylike core of the disk out through the tough disk capsule. A slipped disk occurs when severe forces move the disk out of its normal location. Disk injuries are serious, and they typically require surgical treatment to fix.
Sciatica is a general term for back pain that extends down into the buttock and leg, along the course of the sciatic nerve. Sciatica usually results from pressure on the lumbar and sacral nerve roots that exit the spine to form the sciatic nerve. Arthritis and disk damage are just two of many causes of sciatica.
òLymph Node
The illustration above shows a cross-section of a lymph node. Each node has a capsule and an internal mass of lymphoid tissue. Several lymph vessels carry lymphatic fluid into the node, with a single large vessel carrying the lymphatic fluid back out. The lymphoid tissue is home to many white blood cells of the lymphocyte type. These are the white blood cells that generate antibodies. Lymph nodes also include macrophages (phagocytes) that engulf foreign particles and eliminate them. Lymph nodes are found in groups or chains throughout the body. They serve largely as a barrier to the spread of infection. Lymph nodes are also commonly involved in cancer. This occurs because the cancer cells that metastasize (travel to distant locations) are filtered out by the lymph nodes in a fashion similar to infectious organisms. Enlargement of lymph nodes is often the first sign that a cancer has spread.
Mammography
Breast cancer is a common ailment in the U.S., affecting as many as one in every 11 women during their lifetime. Like most cancers, the prognosis is greatly improved by early detection. The easiest method for enhancing early detection is breast self examination. All women are encouraged to do a self breast examination each month. It is best done at the same point in the menstrual cycle each time. The purpose of the self exam is to note any new or unusual lumps, or a change in the appearance of the breast. Unusual changes should be reported to one's doctor for further evaluation. Another method for increasing early detection of breast cancer is mammography. The picture above shows a women who is having a mammogram done. Several studies have shown that breast cancer deaths can be decreased by routine screening of otherwise healthy women using mammography. Specific recommendations tend to change, but mammography remains a prudent screening test for individuals wishing to increase their chance of early cancer detection.
Melanoma
Malignant melanoma is the most serious form of skin cancer. It appears on the skin initially as a small, but ugly looking dark bump. It will usually have ragged edges and multiple colors within it. It may even start to bleed spontaneously. Melanoma is an aggressive cancer that spreads early in its course. The illustration above shows several melanoma cancer cells entering a blood vessel on their way to spreading to some distant part of the body. This process is called metastasis. Cure for melanoma depends on surgical resection of the disease. If it has spread at the time of surgery, then the prognosis is very poor as melanoma cells are quite resistant to the usual forms of chemotherapy and radiation therapy. The likelihood of distant spread is directly related to the depth that the cancer has penetrated into the skin. This depth is a number in millimeters that is reported when either a biopsy or resection is done. The incidence of melanoma continues to rise in the US. This is attributable to our culture which encourages people to tan themselves. Fair skinned people are at particularly high risk for developing melanoma. It is important that all suspicious skin lesions be promptly reported to a dermatologist or other doctor for further evaluation.
hDigestion
The photomicrograph above shows a closeup of a mucosal cell which lines the inside of the small intestine. Each of the tiny, finger-like projections on this cell's surface are called "microvilli." If we were further away, we could see that the inner lining of the small intestine is itself organized into many small, finger-like projections called "villi." The villi and microvilli together create a surface area within the small intestine that is as large as a tennis court. The main purpose of this lining is to promote the effective absorption of food. This is a job it is quite well designed to perform.
Migraine Headache
Of the many ailments of the brain, the most common is headache. Interestingly, the brain itself contains no sensory fibers, and it cannot actually cause pain. Instead, headache pain comes from the meninges which cover the brain, and the scalp, with its muscles and blood vessels. Headaches are usually a response to external stimuli. Only rarely are they indicative of a serious underlying disorder.
The most severe headache type is migraine. Migraine headaches are usually accompanied by nausea, vomiting, and disturbances of vision. The disturbances of vision precede the pain and are called an aura. Other neurologic symptoms such as weakness can also occur. Patients experiencing a migraine headache usually choose to lie very still in a dark room while waiting for the pain to subside. Migraine headaches are relatively common, affecting three times as many women as men. Migraine sufferers typically report a definite pattern to their headaches, and they can report what stimuli bring them on. Most migraine sufferers experience their first attack before the age of 20. There is no single cause of migraines, but the tendency to get migraines does tend to run in families. A new medication, sumatriptan, shows promise for the relief and prevention of migraine attacks for many patients.
Æ Malaria
Malaria is a parasitic disease spread by the bites of Anopheles mosquitos like the one shown in the illustration above. The parasites responsible for malaria are single-celled organisms called plasmodia. The plasmodia spend part of their life cycle in humans and the remaining part in the Anopheles mosquitos. The plasmodia reproduce in human red blood cells. When the plasmodia are mature, the red blood cells burst and release more plasmodia which then go on to infect even more red blood cells. The bursting of the red blood cells tends to occur in cyclic fashion, every two or three days depending on the type of malarial parasite; there are four different types. When the red blood cells burst, it produces severe chills (rigors) followed by a very high fever. These are the characteristic symptoms of malaria. Malaria is a serious illness that is oftentimes fatal because of all the burst red blood cells which can cause failure of the kidneys and liver. The broken red blood cells can even block blood vessels to vital organs such as the brain, leading to convulsions and coma.
Malaria is present in much of the tropics throughout the world. In Africa alone, malaria kills more than a million infants and children every year. Those that survive develop some measure of immunity. The World Health Organization has embarked on a massive effort to control malaria with only limited success. The mosquitos have developed resistance to the insecticides, and the plasmodia that cause malaria are developing resistance to the drugs normally used to treat the disease. It is very unlikely that anyone would contract malaria in the United States, but about 1,000 US citizens contract malaria each year as a result of travel abroad. It is absolutely necessary for people traveling to endemic malaria regions to take medications that inhibit the malaria parasites from growing, and to take precautions to avoid being bitten by mosquitos.
Of note, sickle cell disease has an important relationship to malaria that is easily explained. Normal people have two copies of the gene (DNA segment) that specifies how to make a beta hemoglobin chain. Sickle cell disease occurs when both of these copies are replaced with abnormal sickle cell versions. Recall that red blood cells are entirely filled with hemoglobin molecules. People with two normal beta hemoglobin genes make normal hemoglobin, and are very susceptible to contracting malaria. People with one normal gene and one of the sickle cell genes make a hybrid form of hemoglobin that renders the red blood cells more resistant to malaria. People with two copies of the sickle gene produce sickle cell hemoglobin which causes sickle cell disease. Over the thousands of years that people have been exposed to malaria, there has been strong selective pressure to keep the sickle cell gene around, despite the fact that it causes a serious disease when someone winds up with two copies of it.
ß3-D Body Adventure
Click directly on the body to begin exploring. To move the body to a new position, click on the rotate body icon. Use the arrow keys or move the mouse to rotate the body. Click the mouse, or hit any key to get a cursor.
bBrain Imaging
Along with CT scanning, magnetic resonance imaging (MRI) has come into widespread use in recent years for imaging the brain and spinal cord. The photograph above shows a patient lying on the gantry of an MRI scanner. The basic principles of physics that make MRI possible have been known since the 1940's, but it wasn't until the 1980's that doctors were able to use this knowledge to make useful images of the body. In most situations, MRI provides better contrast between normal and abnormal parts of the brain than CT scanning does. This makes the diagnosis of disease easier. On the other hand, MRI machines are much more expensive to purchase and operate than CT scanners, and an MRI exam takes much longer to perform, making the test unsuitable for very ill patients. Also, patients hooked up to pumps or other machines with metallic parts cannot be brought into the vicinity of the MRI because of its strong magnetic field. Imagine the sight of all these metal objects flying into the magnet. For the foreseeable future, CT and MRI will remain complementary methods of studying the brain and spinal cord.
Γ Pictures from Magnets
Magnetic resonance imaging (MRI) is a valuable diagnostic technique that has been in general clinical use since the early 1980's. MRI provides doctors with very high quality images of the body without using x-rays. MRI works by detecting weak radio signals that are emitted from the hydrogen nuclei (protons) within the body. This works well because each water molecule (H2O) contains two hydrogen nuclei, and nearly 99% of the molecules in the body are water molecules. Because water molecules are small, however, the body is only about 60% water by weight.
During the MRI exam, the patient lies in a large, powerful magnet. All the hydrogen nuclei (protons) in the body promptly align with this magnetic field. Normally, these protons are all tumbling about randomly. The MRI machine is able to align them only because its magnetic field is more than 10,000 times stronger than the usual magnetic field on the earth. After getting all the protons into alignment, the MRI machine emits a strong radio frequency pulse which briefly knocks all the protons back out of alignment. As the protons come into alignment once again, they emit a weak radio signal of their own which is detected by the machine. The strength of this signal depends both on the concentration of the protons, and what else is around them. For practical purposes, the concentration of protons is the same as the concentration of water. For instance, bones have very little water, so they have almost no signal and appear black with MRI. In contrast, fat has lots of water, and it emits a bright signal which appears white with MRI. The MRI machine is able to distinguish the signals coming from each tiny little piece of tissue and then recombine them to form an exquisitely detailed image.
MRI has found widespread use in many areas of medicine. It is a particularly valuable method for imaging the brain, spinal cord, spine, shoulder, and knee. Its value in imaging other parts of the body continues to grow as radiologists learn more about how to perform MRI exams. There are no known risks or side effects associated with MRI. There is no radiation, and the test can be performed repeatedly without adverse effect. However, MRI should not be done on some people with metal implants within the body, and on people with pacemakers or other electrical devices that are sensitive to high magnetic fields. Also, the tunnel like hole in the magnet where the patient lies causes great psychological stress for people with claustrophobia.
┘ Nerve Fibers
A nerve is a bundle of nerve fibers that all travel together to the same location. Each of the nerve fibers (axons) comes from a separate neuron. The photograph above shows a bundle of several axons. There are 31 pairs of spinal nerves which exit from the spinal cord. Several of these spinal nerves join together to form the sciatic nerve which is the largest nerve in the body. The sciatic nerve supplies the leg with both motor (movement) and sensory nerve fibers.
There is a very specific pattern to the way sensory neurons travel from the surface of the skin to the spinal cord. This is called the dermatome pattern. The word dermatome is related to the word dermis, meaning skin. The dermatomes are a series of rings that can be drawn on a picture of the body. Each ring is connected to the spinal cord at a specific level. When a person loses sensation over a particular part of their body, it is possible to look at the dermatome pattern to determine which level of the spinal cord is involved.
The sensory fibers which serve the internal organs also enter the spinal cord at specific levels. Interestingly, pain coming from these fibers is not generally perceived as coming from the organs themselves. Rather, the pain is perceived as coming from the area of the skin whose pain fibers enter the spinal cord at the same level as those of the painful organ. As a rule, the internal organ pain fibers do not enter the spinal cord at the same level as the skin which lies directly over the organ. An example of this is heart pain, which is often felt as pain in the neck or left shoulder. This is a very general concept known as referred pain. Doctors can often interpret the descriptions of pain given by patients to determine where the real problem is within the body.
Surprisingly, people are born with all the neurons they will ever have. When the cell body of a neuron dies, it is gone, and it will never be replaced. Peripheral nerve injuries typically affect only the axons, however, and not the cell bodies. When a peripheral nerve is cut, the distal segment of each injured axon degenerates, and the proximal segment begins growing to replace the lost distal segment. This is possible because the proximal axonal segments are still attached to the cell bodies. If the severed ends of the nerve are close together, the channels left by the old axons help guide the new axons to the right location. This regeneration of axons is a very slow process. Axons only grow at the rate of about 1 inch (2.5 cm) per month. Unfortunately, this healing process is rarely perfect. People are often troubled to find that their bodies do not do what they expect them to do after the axons have grown back. The ability of neurons to regenerate their axons is strictly limited to the peripheral nervous system. Neurons in the spinal cord and brain (CNS) are in some way different, and they cannot repair themselves after injury. This is why spinal cord injuries typically result in permanent disability.
3Nerve Cell
The basic function of the nervous system is to transmit messages from one place to another. The nerve cells which do this job are called neurons. Neurons can vary widely in their shape, but they all have several basic things in common. Like all cells, neurons have a cell body. These cell bodies have many short branches coming off of them called dendrites. Dendrites allow communication with nearby neurons. Each neuron also has a single long branch called an axon. Axons permit messages to be carried to distant neurons in other parts of the body.
There are three basic types of neurons. These are sensory neurons, motoneurons, and interneurons. Sensory neurons carry signals from their sense receptors in the periphery back to the central nervous system (CNS). Motoneurons carry signals from the CNS to the muscles and glands within the body. Interneurons do the communicating within the CNS itself. For each sensory neuron, there are about 10 motoneurons and 100 interneurons in the body. Apparently, many more neurons are required to decide what to do in response to incoming signals than are required to get those signals.
Neurons actually function by conducting electrical signals down the length of their axons. The axons are wrapped with myelin cells which serve just like the insulating material that surrounds regular copper wires. These electrical signals travel down neurons at speeds over a hundred miles per hour. This seems quite fast unless you compare it to real copper wires which conduct signals at the speed of light (186,000 miles per second).
sEndorphins
Opium and its derivative morphine have been used to relieve pain for more than 100 years. It wasn't until 1973, however, that scientists discovered the actual receptors in the brain that morphine binds to. This discovery raised the question of why all people would happen to have receptors for a chemical produced from poppy flowers. The question was soon answered by the discovery of endorphins, the natural molecules produced by the body that react with the morphine receptors. The name endorphin comes from the phrase, endogenous (self) morphine. Since the initial discovery of endorphins, several related molecules have also been discovered that are called enkephalins. The morphine receptors are now more commonly referred to as opioid receptors. The brain illustration above depicts regions known to contain opioid receptors in yellow and pink.
Interestingly, it is widely thought that acupuncture works by stimulating the production of endorphins. The euphoria some people describe in connection with physical activities like running may also be related to the production of endorphins. Conversely, addiction and tolerance to morphine (and other narcotic analgesics) are thought to be caused by suppression of the body's normal production of endorphins. When the effects of morphine wear off, withdrawal symptoms occur because there is a lack of normal endorphin molecules.
║Osteoporosis
Bones are comprised of fibers of collagen which provide elasticity, and calcium which provides strength. As a normal part of aging, bones tend to lose both collagen and calcium. This loss of bone density with age is more pronounced in women than in men. A person is diagnosed with osteoporosis when this bone loss becomes too great, leaving the bones brittle and prone to fractures. The above picture shows the spongy bone of a patient with osteoporosis. It is noticeably thinner than normal spongy bone.
The rate of bone loss is particularly high in women after menopause. This is because the ovaries stop producing the hormone estrogen which normally helps to maintain bone mass. Other causes of osteoporosis include a diet deficient in calcium and prolonged inactivity. Lost bone cannot usually be replaced, but measures can be taken to slow down the rate of bone loss. Treatment for osteoporosis is thus based on measures to help maintain the remaining bone. These measures include eating a diet high in calcium, increasing exercise, and estrogen replacement for post- menopausal women. Estrogen replacement has been proven to significantly reduce the incidence of fractures in post-menopausal women. The foods highest in calcium are milk and milk products, green leafy vegetables, citrus fruits, and shellfish. Calcium supplements are also useful.
As noted above, the development and maintenance of bone mass requires an adequate intake of calcium and phosphorus. However, the body cannot absorb these minerals without adequate Vitamin D. Osteomalacia is a softening of bones that occurs because of inadequate vitamin D. In children, osteomalacia is called rickets. Vitamin D is obtained both from the diet and from the action of sunlight on the skin. Osteomalacia thus results from a diet lacking vitamin D, a failure to absorb vitamin D, or insufficient exposure to sunlight. Unlike osteoporosis, osteomalacia is quite rare in developed countries.
Conception
The photograph above shows a portion of an ovum with many sperm all trying to fertilize it. This is the last step in the quest to reach the ovum. Only one of the sperm cells will successfully enter the ovum. The outer coating of the ovum is tough. However, the heads of the sperm cells contain a digestive enzyme which breaks down this coating to allow penetration. At the instant that one of the sperm cells breaks through, a reaction takes place which changes the outer coating of the ovum and prevents any more sperm from entering.
µPET Scan
One of the most modern techniques being used to study the brain is positron emission tomography (PET). The picture above shows a PET scanner. Superficially, the machines look very much like CT scanners, but on the inside they are quite different. A PET scan is accomplished by administering a small amount of a radioactive substance to a patient, waiting a short while, and then taking pictures to see where that substance has gone to. PET scanning thus reveals information about the function of the brain. This is different from simply looking at the structure of the brain as CT and MRI scanning do. PET has been used extensively by research doctors to try to figure out what parts of the brain are involved in many different neurologic illnesses including seizures, schizophrenia, and Parkinson's disease. PET has also been used to answer other interesting questions, such as what exact part or parts of the brain are involved in specific activities, like solving math or word puzzles.
∞The Placenta
The illustration above depicts the placenta. The placenta is a fetal organ which develops from the outermost cells of the embryo at its site of implantation in the uterus. The placenta serves as the method by which the developing fetus obtains oxygen and nutrients from the mother, and at the same time eliminates wastes. The structure of the placenta is based on numerous, tiny fetal blood vessels called chorionic villi. The chorionic villi are bathed in maternal blood within the placenta. This allows oxygen, food, and even small molecules like antibodies to freely move between the fetal and maternal circulations. Of note, however, the maternal and fetal red blood cells always stay separated. There is no mixing of the actual blood cells within the placenta. When the fetal blood returns from the placenta, it brings oxygen and needed nutrients with it from the mother. The connection between the placenta and the fetus is called the umbilical cord. This cord is clamped and cut soon after delivery. Throughout pregnancy, the placenta remains firmly attached to the uterus. However, the placenta loses its connection to the uterus within minutes following birth, and it is soon expelled. For this reason it is often called the afterbirth.
.Platelets
Platelets serve as the body's first line of defense to prevent excessive blood loss when a blood vessel is damaged. They normally circulate in the bloodstream in an inactive state. When platelets encounter a damaged vessel, however, they change their shape and become sticky. This causes them to adhere both to one another and to the damaged vessel wall. The illustration above shows a damaged blood vessel with numerous platelets (shown in yellow) rushing in to plug the hole. Platelets are the smallest of the three main types of blood cells. They typically last about nine days in the circulation. One of the many things aspirin does is inactivate platelets irreversibly, preventing then from sticking to one another. This effect is desirable in patients who are prone to forming unwanted blood clots.
OProstate Cancer
The prostate gland surrounds the urethra, sitting just below the bladder in men. Its normal function is to add secretions to semen. As men age, however, it is common for the prostate gland to enlarge. This enlargement may partly cut off the urethra, making it difficult to urinate. Usually, this enlargement is entirely benign, and it is treated only if the symptoms require that something be done. However, one must always be concerned that the changes in the prostate are due to cancer. Prostate cancer is one of the most common causes of cancer in men. Like breast cancer in women, it is a disease that has a good prognosis when it is discovered early and treated. In recent years, there has been a significant increase in the use of prostate cancer screening tests. It is hoped that this trend will save many lives in the future.
$Pulmonary Arteries
The photograph above shows a resin cast of the pulmonary blood vessels. The pulmonary vessels travel together with the airways, following the same course within the lungs. Like the airways, the pulmonary arteries branch again and again to form ever-smaller vessels. The smallest vessels are the pulmonary capillaries which travel through the alveolar walls. The capillaries then join together to form venules and then veins. There are four main pulmonary veins which return the newly oxygenated blood to the left atrium. Interestingly, the lung is the only organ besides the liver to receive a dual blood supply. In addition to the pulmonary arteries, which deliver only deoxygenated blood to the lungs, there are bronchial arteries which supply needed oxygen and nutrients to the lung tissues.
UPulmonary Embolism
Formation of blood clots in the leg and pelvic veins is a relatively common medical problem. These clots can then break off and travel to the lungs where they lodge in the pulmonary arteries. Blood clots in the lungs are called "pulmonary emboli." The illustration above shows severe damage to a lung segment served by an artery which is blocked by a pulmonary embolus. Pulmonary emboli can be life-threatening if they block too much of the blood flow to the lungs. Pulmonary emboli are responsible for more than 50,000 deaths in the U.S. each year.
The strongest risk factor for pulmonary emboli is physical immobility. Patients who are confined to bed after a major operation are at particularly high risk for a pulmonary embolus. Blood thinners are given to people who either have pulmonary emboli or are at high risk for developing them.
cBreathing Test
The photograph above shows a machine used to perform breathing tests. These pulmonary function tests can help in the evaluation of lung disorders such as asthma, emphysema, or cystic fibrosis. Pulmonary function tests can also be used to help determine whether treatment for an illness is working as desired. The machine works largely by measuring the volumes of air moving in and out as the patient breathes. A technologist explains what to do during the test. Sometimes, a blood sample is obtained at the same time as the breathing test to assess how well the lungs are supplying the blood with oxygen.
ÄThe Cerebellum
The cerebellum is the rounded brain structure which lies beneath the cerebrum and behind the brain stem. It has many deep and narrow fissures which increase its surface area six-fold. The primary role of the cerebellum is to maintain balance and to coordinate voluntary movement. The cerebrum initiates movements like walking or dancing, but the cerebellum is required to make these complex motions work correctly. People with cerebellar disorders have problems such as a staggering gait, hand tremors, and slurred speech. Interestingly, alcohol inhibits cerebellar function. For this reason, drunk people usually exhibit symptoms quite similar to people with cerebellar disorders.
The photograph above shows what the cerebellum looks like under the microscope. It is seen to be organized into three main layers, with the largest cells found in the middle layer. These large cells are called Purkinje's cells. The Purkinje's cells each connect with as many as 100,000 other nerve cells. This very intricate interaction with other parts of the brain enables the cerebellum to fine tune the commands which start within the cerebrum in the motor cortex.
╠Radiation Therapy
Radiation therapy is widely used in the treatment of cancer. Depending on the type of cancer, it may either be used by itself or in conjunction with other forms of therapy. The photograph above shows a machine that is used to deliver radiation therapy. Initially, doctors will calculate the correct dose of radiation needed to kill the cancer cells without unduly damaging normal, healthy tissue. Next, they calculate the best angle from which to direct the x-ray beams. Finally, marks are made on the skin, and a number of separate radiation sessions are performed. There is generally no discomfort involved. For cancer types that respond well, radiation therapy is an extremely useful method of treatment.
╘Red Blood Cell
The picture above shows a single red blood cell. Red blood cells function by carrying oxygen to every part of the body, and then carrying carbon dioxide back to the lungs. Red blood cells are very well designed to perform this important job. First, they are packed full of hemoglobin, which functions as the oxygen carrier. Interestingly, red blood cells have no nuclei, a feature which makes even more room for hemoglobin. Second, they are shaped like disks. This shape greatly increases their surface area compared with a sphere of the same volume. The large surface area is important because it improves the efficiency of oxygen transfer between hemoglobin and the tissues where the oxygen is needed. Red blood cells are formed in the bone marrow, and they have an average life span of about 120 days. After this period of time, red blood cells tend to become misshapen and they are removed from the circulation by the spleen.
Red cells normally comprise about 40% of the blood volume. When doctors measure this number, it is called the hematocrit. Sometimes the number of red blood cells drops too low. This condition is called anemia. Most generally, anemia results either because too few red blood cells are being made, or because they are being destroyed prematurely. The most common cause for underproduction of red blood cells is iron deficiency. Iron is a necessary component of hemoglobin, so iron deficiency results in inadequate formation of new red blood cells.
¬Diabetes
Diabetes mellitus is a common disorder caused by insufficient insulin production. Without adequate insulin, the body fails to use glucose (sugar) properly. The blood sugar level rises in the blood, and the extra blood sugar is eventually spilled into the urine. This leads to the classic symptoms of increased urination and excessive thirst. There are two main types of diabetes, insulin dependent diabetes (type 1), and non-insulin dependent diabetes (type 2). Type 1 diabetics are usually diagnosed between the ages of 10 and 16. In these people, the pancreatic cells that normally make insulin are completely destroyed. As the name implies, these people must receive replacement insulin in order to avoid severe symptoms. Even with regular insulin replacement and tight control of their blood sugar level, most type 1 diabetics develop complications over the years. The most common problems include retinal damage, kidney damage, general nerve damage, and higher than normal rates of atherosclerosis. The illustration above shows an eye that has sustained some damage to the retina because of diabetes. The reason for all these long term problems is not completely understood. Type 2 diabetics are quite different. They develop their disease gradually, and they can usually be treated with diet modification. Medications are also available if necessary. These people tend to be obese, and they are much older than type 1 diabetics.
¼The Retina
The retina is the light sensitive surface at the back of the eye. The photograph above shows a picture of the retina as taken with an instrument called an ophthalmoscope. The retina contains a vast number of specialized nerve cells called rods and cones that convert light rays into nerve signals. The cones provide color vision, and are most concentrated at the fovea. The fovea can be seen in the photo above as the region on the left side without any blood vessels crossing it. Because of their dense concentration, the cones in the fovea provide the finest resolution vision. The rods are much more sensitive to light than the cones, but they only provide black and white vision. Next time it is dark out, notice that you only see in black and white. All of the rods and cones connect with nerves whose signals exit from the eye via the optic nerve. The optic nerve, along with the retinal artery, pierces the eye at the optic disk. The optic disk is visible in the picture above on the right side. There are no rods or cones in the optic disk which creates a small blind spot on the retina. It is possible to demonstrate this blind spot, but people are not normally aware of it.
wIntestinal Virus
The illustration above shows a single rotavirus. Worldwide, it is one of the most common viruses that can infect the digestive system and cause gastroenteritis. The rotavirus is easily spread from person to person in a family or other group setting. Rotaviruses are also found in a number of animal species. Rotavirus infection is particularly problematic in infants and young children, and it is responsible for many deaths in undeveloped countries were medical care is inadequate. The rotavirus causes illness by invading the lining of the duodenum and the upper small intestine. The intestinal villi are transiently damaged, but they rapidly regenerate their lining. Illness typically begins with one or two episodes of vomiting followed by diarrhea. Uncomplicated cases resolve in about one week. Treatment requires only rest and adequate fluid intake to prevent dehydration.
`Jonas Salk
In the mid-20th century, polio raged as a major health problem. Polio is caused by an infectious virus that brings on paralysis and disability by damaging nerve cells. In 1954, Jonas Salk and his colleagues were able to build on the work of Edward Jenner by demonstrating that people who were exposed to a killed polio virus preparation would develop lasting immunity to the disease. The picture above shows Dr. Salk administering this vaccine to a child. The Salk polio vaccine was widely used between 1956 and 1960 in the United States, with dramatic results. In the early 1960's, a second polio virus vaccine was developed by Dr. Sabin. It consists of live but severely weakened polio viruses that can induce immunity but cannot cause disease. The chief advantage of this vaccine is that it can be administered orally rather than requiring injection.
Sickle Cell Disease
Many different disorders of hemoglobin production have been discovered. In general, these disorders are divided into problems with heme production (porphyria), and disorders of globin production. Disorders of globin chain production are called "hemoglobinopathies." Hemoglobinopathies can be further divided into those in which abnormal globin chains are produced in normal quantity, and those where normal globin chains are made in inadequate quantity (thalassemias). One of the most common hemoglobinopathies is sickle cell disease. Sickle cell disease is an illness that results from a single small substitution in the hemoglobin beta chains. These modified hemoglobin molecules have a tendency to clump and distort the usual smooth shape of the red blood cells.
├
Electricity in the Brain
The constant activity within the brain produces characteristic electrical signals that can be recorded with an EEG (electroencephalogram) machine. The technique for recording these brain waves has been used in medicine since 1928. It is a simple, painless test that takes only about an hour. A number of small electrodes are placed on the scalp and connected to a recording device. Recordings are usually made with the patient at rest, with the eyes open and shut, during and after hyperventilation, and while looking at a flashlight. All of these situations produce characteristic looking brain waves.
An EEG is most frequently obtained for people who are suspected of having a seizure disorder (epilepsy). Epilepsy is a common disorder that results from unorganized electrical discharges in the brain. About 1 in 200 people have epilepsy. There are a few different types of seizures. Grand mal seizures are the type that people are most familiar with. During a grand mal seizure, the chaotic electrical activity spreads to the whole brain causing the patient to lose consciousness and fall down, often with wild jerking motions. Other types of seizures, including absence seizures and partial seizures, are much less dramatic. Contrary to folklore, it is a bad idea to place anything (like a tongue protector) in the mouth of a person having a grand mal seizure. Loosening of tight clothing around the neck, and placement of something soft beneath the head are the only things that a bystander should do. An ambulance should be called if it is a person's first seizure ever, the seizure continues for more than five minutes, or another seizure follows soon after the first.
In addition to evaluating seizures, EEG machines have been used extensively to study sleep. EEG recordings of people during sleep show two grossly different patterns. One pattern is produced during REM (rapid eye movement) sleep, and the other during NREM (nonrapid eye movement) sleep. These sleep types are named this way because the eyes actually do flutter rapidly when people are in REM sleep. During REM sleep, the brain becomes very active electrically, producing an EEG pattern similar to that of an awake person. In contrast, the electrical activity slows down dramatically in NREM sleep. NREM sleep produces much lower frequency waves on an EEG recording. Normal sleep is characterized by alternating periods of NREM and REM sleep. Adults spend about 80% of their sleeping time in NREM sleep, but the periods of REM sleep become longer and more frequent as sleep continues. People awakened during REM sleep often report vivid dreams. Sleep appears to be a fundamental human requirement, but its exact function remains poorly understood.
╦Sperm Production
The male sex cells are called "sperm." They each have a tiny head containing the genetic material, and a long tail used to swim towards an egg cell. Sperm cells are quite small, measuring only 0.002 inches (0.05 millimeters) in length. Sperm are produced by the testes in a process referred to as spermatogenesis. This process begins in the seminiferous tubules and is completed in the epididymis. The original cells from which the sperm grow contain 46 chromosomes in humans. By a special division called "meiosis," this number is cut in half so that the sperm cells contain only 23 chromosomes. These 23 chromosomes can then unite with an egg, also containing 23 chromosomes, to make a new individual.
╟Skeletal Muscle
There are more than 600 skeletal muscles in the body. Skeletal muscles are also called "voluntary muscles" because they are responsible for purposeful movement of the body such as running and jumping. The photograph above shows a skeletal muscle fiber. The brain sends signals to each and every skeletal muscle fiber, enabling us to perform actions when we wish to do them.
There are three different types of muscle in the body: skeletal muscle, smooth muscle, and cardiac muscle. All three types of muscle are composed of fibers that permit movement through coordinated contraction and relaxation. At the microscopic level, the three types of muscle share a common mechanism for contracting. The basic working elements are actin and myosin filaments. When a muscle contracts, the individual myosin filaments slide over the actin filaments much like an extendable ladder does when it closes. This action causes the overall length of the muscle to shorten.
σBlood Smear
A blood smear is obtained by placing a drop of blood on a glass slide and smearing it to thin it out. The blood smear is then treated with special stains to make the blood cells easier to see. After drying, the blood smear is examined under the microscope to inspect for any abnormal cells. The picture above shows a section from a blood smear containing only white blood cells. When examining a blood smear, it is important to look at both the total number of white blood cells and the relative proportions of the different types of white blood cells. Either or both of these things will usually be abnormal in patients with a serious infection or with leukemia. Of course, there are many other reasons for abnormal white blood cell counts that are more benign. Besides examination of the white cells, it is important to look at the red cells for abnormalities. Sickle cell disease and malaria are just two of many blood diseases that are best diagnosed by looking at the blood smear.
Smooth Muscle
Smooth muscles are found within the organs and blood vessels. They are responsible for many body functions such as movement of food through the digestive tract, and contraction of the uterus during childbirth. As evident in the photograph above, smooth muscles are much less organized than skeletal or cardiac muscle. They are comprised of spindle-shaped cells that are grouped in bundles. Smooth muscles are also referred to as "involuntary muscles" since they are not under conscious control. Instead, they are controlled by the autonomic nervous system. The autonomic nervous system allows the brain to control many body functions without requiring conscious thought. Digestion, blood pressure, and temperature regulation are examples of such body functions.
ôSwimming Sperm
The photograph above shows a single sperm cell, close up against the wall of the uterus. The sperm cell at this point has already survived a major part of the long journey toward the ovum. Of the 300 million sperm that begin the quest, most succumb to the inhospitable environment within the vagina. Many more sperm are lost while trying to navigate through the mucus which blocks the passage through the cervix into the uterus. Those sperm that make it this far continue to swim upwards toward the fallopian tubes and the waiting ovum. Half of the sperm will inevitably enter the wrong fallopian tube but, of course, half of them will stay on track.
{The Spinal Cord
The spinal cord travels down from the brain through the center of the spine. All communication between the body and the brain travels through the spinal cord. The brain and the spinal cord together make up the central nervous system (CNS). The picture above shows a cross-section through the spinal cord. In the middle, there is a dark, butterfly shaped region called the grey matter. Surrounding the grey matter is the white matter.
The grey matter contains all of the nerve cell bodies. These nerves cells include motor neurons and interneurons. Motor neurons are involved with directing movement. Each motor neuron does this job by sending a single long projection (axon) out into the periphery to direct the activity of muscle fibers. Interneurons are contained entirely within the CNS. They function by conveying messages between other neurons. Sensory neurons are a third type of nerve cell. These neurons have their cell bodies outside the spinal cord, but they send processes into the spinal cord to communicate important sensory information such as temperature, pressure, and pain.
The white matter is comprised of nerve fiber tracts. These tracts are of two basic types. Ascending fiber tracts travel up to the brain to convey sensory information. Descending tracts travel down from the brain to convey motor signals. These tracts are necessary for normal sensation and movement throughout the body. Damage to the spinal cord at any level tends to cause loss of sensation (anesthesia), and loss of movement (paralysis) below the level of the injury. Oftentimes, these problems are permanent because spinal cord neurons are unable to regenerate if the are damaged.
There are 31 pairs of spinal nerves that branch off from the spinal cord. One pair of these nerves leaves the spine at every level from the first cervical vertebrae to the coccyx. The spinal cord itself ends at the level of the first or second lumbar vertebrae, but the spinal nerves continue to travel downward so that one pair leaves at each level of the spine. The tangle of nerves below the end of the spinal cord is called the cauda equina or "horse's tail."
îStroke
Stroke occurs when the blood supply to part of the brain is cut off for long enough to cause the death of that part of the brain. This does not take very long. Neurons in the brain can only live for about four minutes without oxygen. Another condition closely related to stroke is transient ischemia attack (TIA). A TIA initially seems like a stroke, but the symptoms quickly disappear. TIA's occur when the blood supply to a part of the brain is interrupted for long enough to stun the affected cells, but then restored before cell death occurs. Strokes are fatal in about a third of all cases, a percentage similar to that observed with heart attacks. For the survivors, a stroke can be quite devastating due to the loss of important brain functions. Sometimes, however, another part of the brain is able to take over the functions of the lost part of the brain.
The risk factors for having a stroke are generally the same as those for having a heart attack. The most notable are high blood pressure and atherosclerosis. A recent heart attack is itself a risk factor for stroke because of the tendency for blood clots to form in the heart and then travel upwards to the brain. Several studies have shown that aspirin taken every day can decrease the chances of a having a stroke in patients who have previously suffered from a stroke or a TIA. Aspirin works in this way by preventing blood clots from forming. It has also been shown that a small dose of aspirin every day can decrease the rate of heart attacks, even in patients who have not previously had any symptoms. Many doctors thus recommend that their patients take a single baby aspirin every day.
aNerve Communication
At their end, nerve axons usually branch into many small terminals which come into close contact with the dendrites of other neurons. The connection between two neurons is called a synapse. The axon and the dendrite never actually touch. There is always a small gap called the synaptic cleft. The photograph above shows a synapse. When an electrical signal reaches a nerve terminal, it causes the nerve to release neurotransmitters. Neurotransmitters are chemicals which travel the short distance to the nearby dendrites. The neuron that releases the neurotransmitter is called the pre-synaptic neuron. The neuron receiving the signal is called the post-synaptic neuron. Depending on the type of neurotransmitter released, the post-synaptic neurons are either encouraged (excited) or discouraged (inhibited) from firing. Each neuron communicates with many other neurons at the same time. Since all a neuron can do is fire or not fire, its behavior is always based on the balance of excitatory and inhibitory influences acting on it at that moment. Neurons are able to refire up to several times per second.
┐Male Reproductive System
The illustration above shows part of the male reproductive system. Sperm production begins in the innumerable seminiferous tubules within the two testes. A close-up of a seminiferous tubule is shown along with a developing sperm cell. Sperm then move into the epididymis where they mature. Shortly before ejaculation, the mature sperm are propelled from the epididymis into a long tube called the "vas deferens." The vas deferens carries the sperm to the seminal vesicles, which add seminal fluid to the sperm cells. The semen then travels along two short ducts to the urethra. Lastly, the urethra passes through the prostate, which adds more secretions to the semen before it leaves the body.
╛Thrombus
A platelet plug is merely the first step in the process of stopping blood loss when a blood vessel is damaged. The activated platelets and damaged vessel walls also secrete chemicals which begin the blood coagulation process. This process is a complex cascade that results in the formation of fibrin strands. The picture above shows a number of red cells trapped within a mesh of fibrin strands. This mesh is referred to as a thrombus. The coagulation cascade is designed to permit significant amplification of the signal to clot. Activation of just one molecule of the first factor in the cascade can result in the formation of 30,000 fibrin molecules at the site of the injury. At the same time, it is important that blood clots do not form when they are not needed. There are also anti-coagulation (thrombolytic) factors in the blood that rapidly dissolve inappropriate clots. A delicate balance between the pro- clotting and anti-clotting mechanisms is always maintained.
There are a large number of clinical disorders affecting the coagulation mechanism. The most well known is hemophilia, a disease that is present in about 1 in every 10,000 males born. It is caused by a lack of factor 8, one of the chemicals in the coagulation cascade. Without this factor, the cascade fails and fibrin strands are not formed. Hemophiliacs thus suffer from frequent and severe bleeds. Treatment involves the administration of the missing coagulation factor 8.
/Spongy Bone
Bones are not simply solid. Beneath the hard outer shell of compact bone, there is a core composed of spongy bone. The complex structure of spongy bone is shown in the photograph above. The gaps in the spongy bone are filled with a soft fatty tissue called "marrow." Bone marrow can be either red or yellow in color, depending on how much fat is found within it. Red bone marrow is responsible for producing most of the blood cells within the body. At birth, all the bones of the body contain red marrow. As we mature to adulthood, much of the red marrow is replaced by the more fatty, less active yellow marrow. This is most notable in the long bones of the arms and legs. In adulthood, red marrow is limited mostly to the skull, spine, shoulder blades (scapulae), clavicles, ribs, sternum, and pelvis.
╓ The Tracheal Lining
The photograph above shows a portion of the tracheal lining. The lining consists of two main types of cells, goblet cells and ciliated cells. The goblet cells secrete a sticky mucus which coats the respiratory lining and traps foreign particles that come from the air we breathe. The ciliated cells have numerous tiny hairs (cilia) on their surfaces which continuously beat in unison. This action sweeps the sticky mucus with its trapped particles up and out of the lungs.
Of note, cigarette smoking is very toxic to the cells which line the respiratory tree. The smoke kills many of these cells and causes inflammation of the airways. The normal protective function of the respiratory lining is thus impaired. This condition is called bronchitis. The chronic coughing and increased susceptibility to upper respiratory infections seen in smokers is due to bronchitis. Other causes of bronchitis besides cigarette smoking include infection with either bacteria or respiratory viruses, and inhalation of toxic chemicals.
Cystic fibrosis (CF) is another cause of bronchitis. It is an inherited disease that is caused by a defective gene. People who inherit a single copy of the CF gene from one of their parents, and a normal copy of the gene from their other parent, are called carriers. CF carriers can pass on the gene, but they exhibit no symptoms. In contrast, people who inherit two copies of the CF gene, one from each of their parents, develop cystic fibrosis. The CF gene is thus called a recessive gene. The tracheal lining in cystic fibrosis patients secretes mucus that is much thicker than normal. The ciliated cells are unable to sweep out this mucus and the airways tend to get clogged up. Cystic fibrosis patients suffer repeated bouts of bronchitis and pneumonia that results in permanent lung damage. This lung damage includes the formation of both cysts (dilated airways) and fibrosis (scar tissue), hence the name of the disease. The CF gene is quite common in the caucasion population, about 1 in every 22 people are carriers. This means that both the man and the woman will be carriers in about 1 in every 500 couples. One-quarter of the children from these couples will inherit the abnormal CF gene from both parents. This accounts for the finding that about 1 in 2000 babies born to white parents have cystic fibrosis. Of note, tests have become available in recent years to determine if a person is a CF carrier, and whether an unborn baby will develop the disease.
≤Tuberculosis
Tuberculosis is an infectious disease commonly referred to as TB. It is caused by a bacteria which is spread from person to person by airborne droplets either coughed or sneezed up. The bacteria are breathed into the lungs where they begin to multiply. The TB bacteria prefer very well oxygenated environments. Consequently, they have a marked preference for the upper lobes of the lungs where the oxygen level is relatively higher than it is in the lower lobes. In most cases, the body's immune system arrests the infection and healing occurs. In some cases, however, the infection remains unchecked and goes on to spread to other organs. This widespread infection is called miliary tuberculosis, and it has a poor prognosis. In another small percentage of cases, the infectious organisms remain viable within the lungs, but adequately walled off. Later in life, the infection can then resurface when the immune system becomes compromised by age or disease.
Until recently, the incidence of TB had declined in western countries throughout the 20th century. The invention of antibiotics had a monumental impact in the mid-20th century, bringing about a precipitous decline in new cases of TB. Antibiotics also revolutionized therapy, which at that time consisted either of nothing or radical surgery. Unfortunately, TB has been making a resurgence in recent years. This is attributable to the rise of the AIDS virus. Patients with AIDS are at high risk for developing TB because of their immuno- compromised condition. Also, unlike AIDS itself, TB is a very infectious illness that is easily transmitted to others in the community. If this weren't enough, new strains of TB are emerging that are resistant to all the standard antibiotic regimens used to treat TB. It is unclear how large this modern health problem will become. In the meantime, it is prudent for high risk individuals, such as hospital workers, to be skin tested for TB regularly, and to take antibiotics if their TB skin test becomes positive.
╤Twins
Two babies sometimes result from a single pregnancy as shown in the illustration above. Twins can be either identical or fraternal. Identical twins develop from a single ovum which splits into two groups of cells soon after fertilization. Identical twins are also called "monozygotic twins," meaning one zygote. Monozygotic twins always look remarkably similar because they are genetically identical. Fraternal twins develop from two separate ova which are each fertilized before implanting in the uterus. Fraternal twins are also called "dizygotic twins," meaning two zygotes. Dizygotic twins may or may not be of the same sex since they are quite independent of one another. The frequency of twin births is about 1 in 90 pregnancies. Dizygotic twins are more likely to occur in women who have a family history of twins, and women who have had many babies before. In contrast, the development of monozygotic twins is random, and these factors do not play a role.
NThe Ureters
The ureters are the long muscular tubes which connect the kidneys to the bladder. Like the intestine, the walls of the ureters contain smooth muscle which contracts in rhythmic fashion to propel the urine down into the bladder. These rhythmic contractions are called "peristalsis." There is a one-way valve at the entrance of each ureter into the bladder. These valves prevent urine from backing up into the ureters and the kidneys. Occasionally, these valves may not work properly, leading to reflux (backwards flow) of urine. This is the most common cause of kidney infections.
Ultrasound
Ultrasound examinations have become a very routine part of pregnancy. The photograph above shows a picture of an ultrasound probe. This hand-held device emits high frequency sound waves that bounce off the developing fetus and other internal structures. The probe then "listens" for the returning echoes to form an image. These sound waves are of very low energy, and the technique is entirely safe. Ultrasound waves do not penetrate well through air. For this reason, a gel is always used to improve the contact between the probe and the person being scanned. Also, with fetal ultrasound, the examination works better if the mother has a full bladder. The full bladder serves as an ultrasound window to see the fetus through, since the sound waves travel so well through the fluid. Although routine prenatal scanning has become commonplace, studies are beginning to show that there is no measurable difference in the overall pregnancy outcome between groups of women who have ultrasound and similar groups of women who don't.
╓Heart Valve
The pumping action of the heart depends on the proper function of the heart valves. There is a single one-way valve at the exit of each of the four chambers. Beginning on the right side of the heart, the four valves are the tricuspid valve, the pulmonary valve, the mitral valve, and the aortic valve. The closing of these valves is responsible for the characteristic "lubb dupp" sounds made by the heart when it beats. The first sound occurs when the tricuspid and mitral valves close. The second sound occurs when the pulmonary and aortic valves close.
The valves are held in place partly by small muscles called papillary muscles. The picture above shows part of the mitral valve and one of its papillary muscles. Generally the valves last a lifetime, but they sometimes become damaged. Any of the valves can become either too leaky (regurgitant), or too tight (stenotic). Regurgitant valves stress the heart by allowing the blood to flow partly backwards. Stenotic valves stress the heart by resisting the normal forward flow of blood. Conditions that can damage the valves include rheumatic fever and endocarditis. If a heart valve becomes damaged enough, it is generally best to replace it with an artificial valve.
?Circulation
One of the landmarks in medical history was William Harvey's discovery that blood flows through the body in a continuous, closed loop. The circulation begins with the left ventricle pumping blood into the aorta, the body's main artery. Next, the aorta goes on to branch again and again to form smaller and smaller arteries. The smallest arteries are called arterioles. The arterioles connect with the capillaries which are no wider than a single blood cell. The red blood cells travel slowly through the capillaries in a single file line. This allows the blood cells to come close to the walls of the capillary in order to release their oxygen and pick up carbon dioxide. The capillaries then come back together to form tiny venules. Finally, the venules join together to form veins that carry the blood back to the heart. Once arriving in the heart, blood cells travel on a very similar journey through the lungs. In the lungs, blood cells course through tiny pulmonary capillaries where they release carbon dioxide, and pick up oxygen in preparation for beginning the circulation through the body once again.
The high pressures generated by the left ventricle keep the circulation moving forward through the arteries. The pressures are much lower, however, on the venous side of the circulation. Instead of relying on the heart, circulation on the venous side depends mostly on the contraction of skeletal muscles which squeeze the veins and push the blood forward. Blood always moves forward because there are one way valves within the veins that keep the blood from backing up.
Health and Diet
More and more, people are recognizing the important relationship between health and diet. Many of the most common health problems in Western society have been proven to be diet related. Most notable is atherosclerosis which leads to both heart attacks and strokes. Many forms of cancer appear to be linked to diet as well. Although opinions change as to what the optimal diet should be, it is clear that a low-fat diet reduces the incidence of atherosclerosis and may reduce the incidence of some cancers. Most people agree that a diet high in complex carbohydrates including fruits, vegetables, and grains is best. Meat and dairy products are fine, but needn't be the main part of one's diet. Total fat intake should be kept to only 15% of total calories, if possible.
úLung Scan
The most common method used to try to diagnose blood clots in the lungs is a lung scan. This test is relatively easy to perform. It involves administering a small volume of tiny, radioactive particles that travel to the lungs through the blood. These particles become trapped in the small blood vessels (arterioles) just before the pulmonary capillaries. The picture produced from the radioactive particles shows a normal outline of the lungs, unless there are blood clots which block the blood flow to certain lung segments. In this case, there are wedge-shaped defects where the particles didn't reach the lung tissue because of the blockage. It is also routine to do a breathing test with a radioactive gas. This enables doctors to see if any parts of the lungs are not receiving air. Quite frequently, it turns out that the cause for a person's shortness of breath is a blocked airway instead of a blocked blood vessel.
┐ White Blood Cell
The principal role of white blood cells is to protect the body from infection. There are three main types of white blood cells, each of which plays an important role in the immune system. The three types are granulocytes, monocytes, and lymphocytes.
Granulocytes, the first of the three classes of white blood cells, are themselves divided into three more types. Neutrophils are the most important of these types. Basophils and eosinophils are the other two. A neutrophil is shown in the picture above. Neutrophils have the job of defending the body against invading bacteria. Neutrophils perform this job by simply engulfing the bacteria and killing them. Neutrophils are also called phagocytes, a term which means "engulfing cell." The pus that accumulates at the site of an infection consists almost entirely of neutrophils.
Monocytes are the next major class of white blood cells. Like neutrophils, monocytes are also phagocytes. However, monocytes are much less particular about what they will engulf. Monocytes are required to remove the cellular debris that persists long after a typical infection has been cured.
The last major class of white blood cells is lymphocytes. Lymphocytes are formed both in the bone marrow and in the lymph glands. Lymphocytes are usually divided into B-cells and T-cells. B-cells are responsible for making antibodies. Antibodies are special molecules that are tailor made to bind to nearly any foreign material that enters the body. Once formed, the antibodies help the body to eliminate these foreign materials. The other type of lymphocyte, T-cells, have two main jobs. The first of these jobs is to assist the B-cells with making antibodies. The second job is to recognize and eliminate cells that seem foreign to the body. T-cells are responsible when an organ transplant is rejected. T-cells are also responsible for eliminating otherwise normal cells that have been infected with a virus. This happens because the infected cells have virus particles on their surfaces which make them seem foreign to the body.
Lymphocytes (B-cells and T-cells) are usually very good at distinguishing the body itself from foreign invaders. This is called self tolerance. Occasionally, this process goes awry, and the lymphocytes attack the body as if it was a foreign object. Many different disorders can result from this mistaken immune system behavior. Collectively, these disorders are all referred to as autoimmune diseases.
┤The Knee
The knee is the hinge joint that connects the main bones of the leg (the femur and the tibia). The kneecap (patella) lies over the front of the joint. There are strong ligaments on both sides of the joint, called the medial and lateral collateral ligaments. There are also two ligaments within the joint, called the anterior and posterior cruciate ligaments. All four of these ligaments serve to connect the bones of the knee, and to provide additional stability. Like other moveable joints, the bony ends of the femur and tibia are separated by protective cartilage which serves as a cushion between the bones. There are two of these cartilage cushions in the knee. They are called the medial and lateral menisci.
The powerful quadriceps muscles are responsible for straightening (extending) the leg at the knee joint. These muscles are in the front of the thigh. The kneecap is actually a large bone within the quadriceps tendon. The quadriceps tendon is thus commonly referred to as the patellar tendon. The hamstrings are the muscles which bend (flex) the knee at the knee joint. These muscles are located in the back of the thigh.
There are a number of common knee injuries. Severe twisting of the knee will frequently sprain one of the knee ligaments. The difference between a sprain and a strain is often confused. A sprain occurs when a ligament (fibrous connection between bones) is damaged. A strain occurs when a muscle or tendon is damaged. Running can sometimes injure the knee by straining the patellar tendon. The cartilage cushions (menisci) within the knee are also frequently damaged by severe twisting. A torn meniscus is very painful, and usually requires surgical repair.
┤The Knee
The knee is the hinge joint that connects the main bones of the leg (the femur and the tibia). The kneecap (patella) lies over the front of the joint. There are strong ligaments on both sides of the joint, called the medial and lateral collateral ligaments. There are also two ligaments within the joint, called the anterior and posterior cruciate ligaments. All four of these ligaments serve to connect the bones of the knee, and to provide additional stability. Like other moveable joints, the bony ends of the femur and tibia are separated by protective cartilage which serves as a cushion between the bones. There are two of these cartilage cushions in the knee. They are called the medial and lateral menisci.
The powerful quadriceps muscles are responsible for straightening (extending) the leg at the knee joint. These muscles are in the front of the thigh. The kneecap is actually a large bone within the quadriceps tendon. The quadriceps tendon is thus commonly referred to as the patellar tendon. The hamstrings are the muscles which bend (flex) the knee at the knee joint. These muscles are located in the back of the thigh.
There are a number of common knee injuries. Severe twisting of the knee will frequently sprain one of the knee ligaments. The difference between a sprain and a strain is often confused. A sprain occurs when a ligament (fibrous connection between bones) is damaged. A strain occurs when a muscle or tendon is damaged. Running can sometimes injure the knee by straining the patellar tendon. The cartilage cushions (menisci) within the knee are also frequently damaged by severe twisting. A torn meniscus is very painful, and usually requires surgical repair.
ΣThe Shoulder
The shoulder is a ball and socket joint which connects the arm with the body. Three bones come together to form the shoulder joint. These bones are the humerus (arm), the clavicle (collar bone), and the scapula (shoulder blade). The deltoid muscle sits on top of the upper arm and shoulder. This powerful muscle works to lift the arm away from the body. There is a fluid filled cavity under the deltoid muscle which serves to reduce friction between the muscle and the underlying joint. Occasionally, this cavity becomes inflamed and painful because of excessive motion. This condition is called bursitis. Bursitis can also occur at a number of other joints including the elbow and knee.
The tendons of four muscles merge together around the shoulder joint to form a reinforcing structure called the rotator cuff. The rotator cuff can be damaged by excessive stress. This is why rotator cuff injuries are common among professional athletes, especially baseball pitchers and football quarterbacks. Another common problem is dislocation of the shoulder. In this case, the top of arm (humeral head) comes out of its normal socket (glenoid cavity). Some people have relatively lax shoulder muscles, and are prone to shoulder dislocations.
ΣThe Shoulder
The shoulder is a ball and socket joint which connects the arm with the body. Three bones come together to form the shoulder joint. These bones are the humerus (arm), the clavicle (collar bone), and the scapula (shoulder blade). The deltoid muscle sits on top of the upper arm and shoulder. This powerful muscle works to lift the arm away from the body. There is a fluid filled cavity under the deltoid muscle which serves to reduce friction between the muscle and the underlying joint. Occasionally, this cavity becomes inflamed and painful because of excessive motion. This condition is called bursitis. Bursitis can also occur at a number of other joints including the elbow and knee.
The tendons of four muscles merge together around the shoulder joint to form a reinforcing structure called the rotator cuff. The rotator cuff can be damaged by excessive stress. This is why rotator cuff injuries are common among professional athletes, especially baseball pitchers and football quarterbacks. Another common problem is dislocation of the shoulder. In this case, the top of arm (humeral head) comes out of its normal socket (glenoid cavity). Some people have relatively lax shoulder muscles, and are prone to shoulder dislocations.
┤The Leg
The knee is the hinge joint that connects the main bones of the leg (the femur and the tibia). The kneecap (patella) lies over the front of the joint. There are strong ligaments on both sides of the joint, called the medial and lateral collateral ligaments. There are also two ligaments within the joint, called the anterior and posterior cruciate ligaments. All four of these ligaments serve to connect the bones of the knee, and to provide additional stability. Like other moveable joints, the bony ends of the femur and tibia are separated by protective cartilage which serves as a cushion between the bones. There are two of these cartilage cushions in the knee. They are called the medial and lateral menisci.
The powerful quadriceps muscles are responsible for straightening (extending) the leg at the knee joint. These muscles are in the front of the thigh. The kneecap is actually a large bone within the quadriceps tendon. The quadriceps tendon is thus commonly referred to as the patellar tendon. The hamstrings are the muscles which bend (flex) the knee at the knee joint. These muscles are located in the back of the thigh.
There are a number of common knee injuries. Severe twisting of the knee will frequently sprain one of the knee ligaments. The difference between a sprain and a strain is often confused. A sprain occurs when a ligament (fibrous connection between bones) is damaged. A strain occurs when a muscle or tendon is damaged. Running can sometimes injure the knee by straining the patellar tendon. The cartilage cushions (menisci) within the knee are also frequently damaged by severe twisting. A torn meniscus is very painful, and usually requires surgical repair.
The Skull
The skull consists of the cranium, which surrounds the delicate brain, and the facial bones. The cranium is formed by eight bones: the frontal bone, two parietal bones, two temporal bones, the occipital bone in the back, the ethmoid bone behind the nose, and the sphenoid bone. The face consists of fourteen bones including the maxilla (upper jaw) and mandible (lower jaw). The bones of the skull are quite hard, and protection of the brain is undoubtedly their most important function. Interestingly, several of the bones are hollow, a feature which reduces their weight. Imagine how heavy your head might feel after a long day if these bones weren't hollow. These air filled spaces are called the paranasal sinuses because they are located all around the nose. The membranes which line the sinuses sometimes become inflamed because of allergy or infection. This is a common condition referred to as sinusitis.
All the skull bones except the mandible are held together by immovable joints called sutures. The mandible and the two temporal bones are held together by freely movable joints which are named, not surprisingly, the temporomandibular joints (TMJ). The TMJ's usually work well to permit all the complex motions required for chewing and talking. Some people, however, develop pain in their TMJ's. This condition is called temporomandibular joint syndrome. TMJ syndrome is usually the result of spasm of the chewing muscles. Headaches, facial pain, and various "popping" noises are all common in patients with TMJ syndrome. Treatment is generally directed at reducing the muscle spasms and relieving the pain.
Besides protecting the brain, the other major function of the skull is to house the special sense organs. The eyes (vision), ears (hearing), nose (smell), and tongue (taste) are all located in the skull. The sense of taste is accomplished by the approximately 10,000 taste buds. These are mostly located on the tongue with a few located at the back of the throat. Surprisingly, there are only four different tastes that can be differentiated by the taste buds alone: bitter, salty, sour, and sweet. The taste buds for each of these four different tastes are grouped together on the tongue. Of note, the taste buds for sweet are all located at the very tip of the tongue. Our ability to distinguish a rich range of tastes is actually due to our sense of smell which is much more developed than our sense of taste. The sense of smell is accomplished by special nerve endings that all sit in a small region in the roof of the nose. Our sense of smell is remarkably sensitive. As few as four individual molecules can produce a recognizable smell.
The Skull
The skull consists of the cranium, which surrounds the delicate brain, and the facial bones. The cranium is formed by eight bones: the frontal bone, two parietal bones, two temporal bones, the occipital bone in the back, the ethmoid bone behind the nose, and the sphenoid bone. The face consists of fourteen bones including the maxilla (upper jaw) and mandible (lower jaw). The bones of the skull are quite hard, and protection of the brain is undoubtedly their most important function. Interestingly, several of the bones are hollow, a feature which reduces their weight. Imagine how heavy your head might feel after a long day if these bones weren't hollow. These air filled spaces are called the paranasal sinuses because they are located all around the nose. The membranes which line the sinuses sometimes become inflamed because of allergy or infection. This is a common condition referred to as sinusitis.
All the skull bones except the mandible are held together by immovable joints called sutures. The mandible and the two temporal bones are held together by freely movable joints which are named, not surprisingly, the temporomandibular joints (TMJ). The TMJ's usually work well to permit all the complex motions required for chewing and talking. Some people, however, develop pain in their TMJ's. This condition is called temporomandibular joint syndrome. TMJ syndrome is usually the result of spasm of the chewing muscles. Headaches, facial pain, and various "popping" noises are all common in patients with TMJ syndrome. Treatment is generally directed at reducing the muscle spasms and relieving the pain.
Besides protecting the brain, the other major function of the skull is to house the special sense organs. The eyes (vision), ears (hearing), nose (smell), and tongue (taste) are all located in the skull. The sense of taste is accomplished by the approximately 10,000 taste buds. These are mostly located on the tongue with a few located at the back of the throat. Surprisingly, there are only four different tastes that can be differentiated by the taste buds alone: bitter, salty, sour, and sweet. The taste buds for each of these four different tastes are grouped together on the tongue. Of note, the taste buds for sweet are all located at the very tip of the tongue. Our ability to distinguish a rich range of tastes is actually due to our sense of smell which is much more developed than our sense of taste. The sense of smell is accomplished by special nerve endings that all sit in a small region in the roof of the nose. Our sense of smell is remarkably sensitive. As few as four individual molecules can produce a recognizable smell.
The Spleen
The spleen is an organ whose major functions are to remove worn out or misshapen red blood cells, and to help fight infections. The spleen has a sponge-like internal structure that is filled with lymphocytes and phagocytes. The phagocytes (engulfing cells) do their job by engulfing foreign particles. The lymphocytes perform their role by producing antibodies which help in the elimination of foreign invaders. In the fetus, the spleen actually serves as the site of red blood cell production, but this job is taken over by the bone marrow after birth. Although helpful, the spleen is not an essential organ. If it is either removed surgically or rendered non-functional because of disease, its functions are taken over by other parts of the body. People without spleens, however, do become more susceptible to infections by certain bacteria. The most common cause for spleen failure is sickle cell disease. The abnormal red blood cells damage the structure of the spleen and cause it to stop working usually before the age of ten years.
]The Stomach
The stomach is the hollow, muscular organ where the process of digesting swallowed food begins. Its walls are quite flexible, expanding to a volume of about 1.5 liters (3 pints) after a meal. The stomach lining secretes strong acids and special enzymes that begin to break down the swallowed food. The muscular walls also churn the food which helps to convert the food into a creamy paste. Of note, the stomach wall also contains glands which secrete mucus. This mucus coats the inner lining of the stomach and prevents the stomach from digesting itself. Occasionally, the mucus barrier is disrupted for some reason, leading to the formation of an ulcer. Most ulcers will heal uneventfully with just antacids taken for therapy. Medications that reduce the output of stomach acid can also be used to help heal ulcers and prevent new ones from forming.
The Torso
The torso is the part of the skeleton that protects the internal organs. In the back, the spinal column encases the all-important spinal cord, while allowing the human to maintain an erect posture. The shoulder blades (scapulae) and clavicles provide an attachment point for the upper extremities. The ribs are important for protecting both the lungs and the heart. The pelvic bones serve to protect the organs of the lower abdomen and pelvis. They also provide an attachment point for the lower extremities.
The Torso
The torso is the part of the skeleton that protects the internal organs. In the back, the spinal column encases the all-important spinal cord, while allowing the human to maintain an erect posture. The shoulder blades (scapulae) and clavicles provide an attachment point for the upper extremities. The ribs are important for protecting both the lungs and the heart. The pelvic bones serve to protect the organs of the lower abdomen and pelvis. They also provide an attachment point for the lower extremities.
íUterus and Ovaries
The uterus is a strong, muscular organ with which a woman is able to nourish a fertilized ovum until it has grown into a fetus ready to be born. The uterus has a remarkable ability to grow tremendously during pregnancy, and then rapidly contract back to its normal size soon after delivery. Before fertilization can occur, however, an egg cell (ovum) must be released and a sperm cell must reach it. A carefully orchestrated hormonal process needs to occur in order for an ovum to mature and be released from one of the ovaries. After this, the ovum must be captured by the feathered edges (fimbriae) of the fallopian tube and guided down toward the uterus. For the sperm to reach the ovum, it must pass through the narrow opening to the uterus. This opening is called the cervix. For most of every month, the cervical opening is blocked with thick mucus that is inhospitable to sperm. At the time of ovulation (egg release), however, the cervical mucus becomes thin and conducive to sperm trying to swim up towards the waiting ovum. Whether or not fertilization takes place, the mucus soon becomes thick again, awaiting the next release of an ovum before it changes back.
íUterus and Ovaries
The uterus is a strong, muscular organ with which a woman is able to nourish a fertilized ovum until it has grown into a fetus ready to be born. The uterus has a remarkable ability to grow tremendously during pregnancy, and then rapidly contract back to its normal size soon after delivery. Before fertilization can occur, however, an egg cell (ovum) must be released and a sperm cell must reach it. A carefully orchestrated hormonal process needs to occur in order for an ovum to mature and be released from one of the ovaries. After this, the ovum must be captured by the feathered edges (fimbriae) of the fallopian tube and guided down toward the uterus. For the sperm to reach the ovum, it must pass through the narrow opening to the uterus. This opening is called the cervix. For most of every month, the cervical opening is blocked with thick mucus that is inhospitable to sperm. At the time of ovulation (egg release), however, the cervical mucus becomes thin and conducive to sperm trying to swim up towards the waiting ovum. Whether or not fertilization takes place, the mucus soon becomes thick again, awaiting the next release of an ovum before it changes back.
