Describe the location, function, and structure of the stomach. What are the gastric juices; how is the stomach protected from them? What must food pass through to enter the duodenum from the stomach?
The stomach, a large muscular sac, lies just below the ribs in the upper left-hand part of the abdominal cavity. Besides acting as a storage organ for food, thus permitting discontinuous feeding, the stomach has two other functions. The stomach is composed of three layers, including an outer layer of connective tissue, a thick middle layer of smooth muscle, and an inner layer of connective tissue and columnar epithelial cells. The stomach helps with the mechanical breakup of food. Waves of contraction in the muscular middle layer of the stomach churn the food, breaking it up as well as mixing it with gastric juices. The stomach also aids in the enzymatic digestion of food. Some of the inner layers' glands secrete a mucous lining for the stomach, protecting it from the gastric juices, a mixture of hydrochloric acid and digestive enzymes that are secreted by the other set of stomach-lining glands. The highly acidic mixture of food and gastric juices leaves the stomach for the small intestine through the pyloric sphincter.
