Gastric physiology

Abstract

Our stomach produces about 2L/day of gastric acid secretion/juice. Its high H+ ions (pH=1-2) kill most of the ingested germs; it catalyzes the conversion of inactive pepsinogen to pepsin. The presence of acid/pepsin begins the digestion of dietary protein. However, pancreatic proteases can hydrolyze all ingested protein in the absence of pepsin. An important component of gastric juice is intrinsic factor (IF), which binds vitamin B12 in the duodenum, allowing it to be eventually absorbed in the distal ileum (see B12 absorption of Chap. 9); it is the only indispensable substance of gastric juice. Its deficiency, following gastric surgery or in pernicious anemia, must take injections of B12 or oral B12 with IF. The surface epithelia cells of stomach secrete mucus and bicarbonate that protect the mucosa from acid/pepsin erosion.