The first hormone ever described (1902) — the discovery that founded endocrinology.
Part of the Metabolic & GLP-1 peptides cluster
Overview
Secretin is a 27-amino-acid hormone released from duodenal S-cells in response to stomach acid entering the small intestine. Discovered by Bayliss and Starling in 1902, it was the first substance ever called a hormone and remains a landmark in the history of endocrinology.
Source & context
Biological / chemical source: Duodenal S-cells
Primary research or clinical context: Endogenous hormone; used diagnostically (e.g., pancreatic function and gastrinoma testing)
Historic significance
Secretin's discovery demonstrated that a chemical messenger carried in the blood — not just nerves — could coordinate organs. That insight launched the entire concept of hormones. It gives its name to the 'secretin family' of related peptides that includes glucagon, GLP-1 and GIP.
Physiology and diagnostic use
When acidic chyme reaches the duodenum, secretin signals the pancreas to release bicarbonate-rich fluid, neutralizing the acid and protecting the intestinal lining. Its predictable action is exploited in diagnostic stimulation tests. Coverage here is educational and describes physiology rather than any therapeutic protocol.
Sequence
One-letter sequence commonly cited for Secretin (educational; isoforms and modifications may differ):
HSDGTFTSELSRLREGARLQRLLQGLV
Residues plotted ~100° apart around an α-helix — clustering of one color reveals an amphipathic face.
FAQ about Secretin
What is Secretin?+
Secretin is a 27-amino-acid hormone released from duodenal S-cells in response to stomach acid entering the small intestine. Discovered by Bayliss and Starling in 1902, it was the first substance ever called a hormone and remains a landmark in the history of endocrinology.
Is Secretin an approved medicine?+
Secretin is discussed here as a research / educational topic. Endogenous hormone; used diagnostically (e.g., pancreatic function and gastrinoma testing). This is not medical advice.
What is the typical length of Secretin?+
Secretin is commonly described as approximately 27 amino acids (Hormone).