Physiology of the Small Intestine

Abstract

Food, once ingested, becomes fragmented by chewing and mixed with saliva to facilitate swallowing. Saliva contains the enzyme α-amylase, which degrades the starch in the food. After passing through the oesophagus the food bolus enters the stomach, where it is further kneaded by vigorous contractions of the gastric wall and mixed with gastric juice, which contains pepsinogens and hydrochloric acid. The secretion of gastric juice is regulated by nervous and hormonal factors, especially by gastrin. The stomach serves as a temporary store for the food ingested. By periodic relaxation of the pyloric muscle, small amounts of the chyme are passed into the duodenum. The mode of evacuation of the stomach is dependent on the volume of stomach contents, the osmotic pressure and fat content of the meal, and the acid concentration (192). In addition to nervous reflexes, intestinal hormones probably also play an important role in the evacuation of the stomach.