gastric secretion

Gastric juice contains the enzymes chymosin (in infants) and lipase, the inactive precursor of pepsin (pepsinogen), intrinsic factor, mucin, and hydrochloric acid. The acid is secreted by the parietal cells at a strength of 0.16 mol/L (0.5-0.6% acid); the same cells also secrete intrinsic factor, and failure of acid secretion (achlorhydria) is associated with a failure to absorb vitamin B₁₂ because of lack of intrinsic factor (see anaemia, pernicious) and reduced absorption of iron. Gastric secretion declines with increasing age, as a result of gastric atrophy.

Pepsinogen is secreted by the chief cells of the gastric mucosa, and is activated to pepsin by either gastric acid or the action of existing pepsin; it is a proteolytic enzyme. The only function of chymosin is to coagulate milk; the lipase hydrolyses a proportion of dietary fat.