secretin

Secretin is the gut’s “neutralize the acid” call. When acidic stomach contents arrive in the small intestine, secretin signals the pancreas to flush in watery, bicarbonate-rich fluid that buffers the acid and protects the delicate intestinal lining.

Secretin is a peptide hormone released by S-cells in the duodenum when they sense a drop in pH from incoming gastric acid. It stimulates the pancreatic duct cells and bile ducts to secrete bicarbonate (alkaline) fluid, raising intestinal pH so digestive enzymes can work. It also gently slows gastric emptying and reduces stomach acid production, working in concert with the buffering response.

Secretin holds a place in history as the first hormone ever discovered, identified in 1902 by Bayliss and Starling — the experiment that introduced the very concept of a “hormone,” a blood-borne chemical messenger. Today it is mainly used as a diagnostic agent in tests of pancreatic and gastrin-secreting tumor function rather than as a treatment.