Stomach

A hollow, bag-like organ of the digestive system located in the left side of the abdomen under the diaphragm. Food enters the stomach from the oesophagus and exits into the duodenum. The sight and smell of food, and its arrival in the stomach, stimulate gastric secretion from the stomach lining. Gastric juice contains pepsin, an enzyme that breaks down protein; hydrochloric acid, which kills bacteria and creates the optimum pH for pepsin activity; and intrinsic factor, which is essential for absorption of vitamin B in the small intestine. The gastric lining also secretes mucus to stop the stomach digesting itself. The muscular stomach wall produces rhythmic contractions that churn the food and gastric juice to aid digestion. Partly digested food is squirted into the duodenum at regular intervals by stomach contractions and by relaxation of the ring of muscle at the stomach outlet.