secretin A hormone produced by the anterior part of the small intestine (the duodenum and jejunum) in response to the presence of hydrochloric acid from the stomach. It causes the pancreas to secrete alkaline pancreatic juice and stimulates bile production in the liver. Secretin, whose function was first demonstrated in 1902, was the first substance to be described as a hormone.

secretin (si-kree-tin) n. a hormone secreted from the duodenum when acidified food leaves the stomach. Secretin stimulates the secretion of relatively enzyme-free alkaline juice by the pancreas and of bile by the liver.

secretin A peptide hormone secreted by the intestinal mucosa which stimulates pancreatic secretion.