Asthma is a condition characterized by breathlessness and wheezing.
To understand how asthma causes shortness of breath, one must look at the normal respiratory system.
Air enters the lungs through a large tube known as the trachea, which is supported by concentric rings of cartilage connected to each other by annular ligaments.
The trachea splits into a right and left primary bronchus and from there, each primary bronchus subdivides into secondary and tertiary bronchi.
Tertiary bronchi continue to branch into smaller tubes called bronchioles.
Unlike the larger tubes, bronchioles do not contain cartilage, and must rely on smooth muscle in their walls to keep these airways open.
The smallest and final branch of bronchioles, called terminal bronchioles, end blindly into the alveolar sacs.
Alveolar sacs are made up of grapelike clusters of alveoli.
Within these alveoli, gas is exchanged and vital oxygen enters the bloodstream.
Throughout the bronchiolar tree, mucus is secreted from specialized cells in the walls to trap foreign particles and irritants that may be in the air we breathe.
The walls consist of cells that are covered with cilia, whose main role is to push mucus up and out of the bronchiolar tree, disposing of the trapped particles and irritants.
Looking at a cross section of a bronchiole, its is evident that under normal conditions, there is little resistance offered to the incoming rush of inspired air.
The wall of the bronchiole is relaxed and provides an open airway.
Asthma is a chronic condition in which various irritants cause bronchioles to become inflamed.
Some of the most common irritants are dust mites, pollen, smoke, stress and infections.
These irritants can cause a cascade of events, such as the release of leukotrienes and histamine from leukocytes and mast cells.
The result is inflammation, overproduction of mucous and bronchiole constriction.
All three block the airways, making it difficult for air to move in the lungs, and thus triggering an asthmatic attack.
There are several treatments for asthma.
The most common is epinephrine and related compounds.
Epinephrine stimulates beta-adrenergic receptors in the bronchioles and promotes the dilation of bronchioles.
Epinephrine can be inhaled as a spray to open up clogged bronchioles, which in turn will relieve the symptoms of an asthmatic attack.
