Secretin is a twenty-seven amino-acid peptide produced by S cells that are sparsely scattered throughout the duodenal and jejunal mucosa. Its main physiological function is to stimulate the secretion of watery alkaline juices from the pancreatic ducts. In common with other members of this family of peptides, secretin inhibits secretion of gastric acid and stimulates insulin release, although these effects occur only at pharmacological doses. The main stimulus to secretin secretion is a duodenal pH of less than 4. This occurs rarely, but the secretion of alkaline juices may protect the duodenum in the fasted state.
