Sekretiini

Sekretiini, known in English as secretin, is a peptide hormone produced by S cells in the mucosa of the proximal small intestine, particularly the duodenum. It is released in response to acidic chyme entering the small intestine from the stomach.

The primary role of secretin is to regulate the environment of the small intestine. It stimulates the pancreatic ductal cells to secrete bicarbonate-rich pancreatic juice, which neutralizes gastric acid and provides an optimal pH for digestive enzymes. Secretin also promotes the secretion of bicarbonate by the liver and biliary system. In addition, it can modestly inhibit gastric acid secretion and slow gastric emptying, contributing to feedback control of digestion.

Release is triggered by low pH in the duodenum, and secretin acts on target tissues via secretin receptors, a class of G protein-coupled receptors that activate cyclic AMP signaling in pancreatic and biliary epithelia.

Discovery and naming: secretin was one of the first hormones described, identified in 1902 by William Bayliss and Ernest Starling. Its discovery helped establish the concept of hormonal regulation of digestion, with the name reflecting its role in stimulating secretion.

Clinical notes: historically, the secretin stimulation test was used to assess pancreatic exocrine function and biliary responses. Today, it is less common, having been largely supplemented by imaging and alternative functional tests, but the hormone remains a fundamental example of digestive endocrinology and physiology.