Secretin, also known as secretin, is a polypeptide hormone released by the S cells of the small intestinal mucosa. This hormone is more abundant in the mucosa of the upper part of the small intestine and is less present farther away from the pylorus. Hydrochloric acid is the strongest contributor to the release of this hormone, followed by protein breakdown products, followed by sodium libatate. This hormone mainly acts on the epithelial cells of the small ducts of the pancreas, causing them to secrete a large amount of water and bicarbonate, which increases the secretion of pancreatic juice and the enzyme content is very low. In addition, it can also promote the secretion of pepsinogen, duodenal gland, small intestine gland and insulin release. The main physiological effects are: (1) promoting the secretion of pancreatic juice; (2) antagonize the oxytic effect of gastrin; (3) Inhibition of gastrointestinal motility and gastric emptying.