Secretin

Secretin is a hormone that controls the secretions into the duodenum, and separately, water homeostasis throughout the body. It is produced in the S cells of the duodenum in the crypts of Lieberkühn. Its effect is to regulate the pH of the duodenal contents by the control of gastric acid secretion and buffering with bicarbonate from the centroacinar cells of the pancreas as well as intercalated ducts. It is notable for being the first hormone to be identified. In humans, the secretin peptide is encoded by the SCT gene.

In 2007, it was discovered to play a role in osmoregulation in the hypothalamus, pituitary, and kidney.