Secretin
Hormone that neutralizes duodenal pH and regulates water balance.
Secretin is a peptide hormone produced in the S cells of the duodenum that regulates water homeostasis, influences duodenal pH, and modulates secretions in the stomach, pancreas, and liver. Secretin is encoded by the SCT gene in humans and plays roles in digestion, osmoregulation, and food intake.
- discovered_by
- William Bayliss and Ernest Starling
- type
- Peptide hormone
- gene
- SCT
- primary_function
- Regulates duodenal pH and water homeostasis
- amino_acids
- 27
Lore & Background
They discovered that cutting all nerves to the pancreas did not prevent pancreatic secretion in response to chyme entering the duodenum, indicating a chemical messenger transported via blood. The mature peptide is 27 amino acids long with a helix between positions 5 and 13. It shares sequence similarities with glucagon, vasoactive intestinal peptide (VIP), and gastric inhibitory peptide (GIP). Secretin release is triggered by low duodenal pH (2–4.5) and inhibited by H2 antagonists that reduce gastric acid. Secretin neutralizes duodenal pH by stimulating bicarbonate secretion from pancreatic ductal cells and cholangiocytes, inhibiting gastric acid secretion, and promoting water and bicarbonate from Brunner's glands. Secretin reduces food intake via the central melanocortin system and is used in diagnostic tests for pancreatic function.
Reader's Guide
Although adrenaline was identified earlier, secretin's discovery catalyzed the field of hormonal regulation. Its primary physiological role—neutralizing duodenal pH to enable optimal pancreatic enzyme function—is critical for digestion. Beyond digestion, secretin's roles in osmoregulation and food intake reveal its broader influence on homeostasis. A wave of interest in secretin as a treatment for autism in the 1990s was disproven by NIH clinical trials. Secretin remains a model for understanding hormone action, receptor signaling, and the integration of digestive and fluid balance systems.
Did You Know?
- Secretin is canonically recognized as the first hormone—the term 'hormone' was coined based on its discovery. Adrenaline's physiological effects were described earlier, but it was not identified as a hormone at that time
- The mature secretin peptide is 27 amino acids long and shares 14 of those positions with glucagon.
Frequently Asked Questions
Who is Secretin?
Secretin is a 27-amino-acid peptide hormone made by the S cells of the duodenal wall and encoded by the SCT gene in humans. It holds the distinction of being the first hormone ever identified, marking the birth of endocrinology.
What are Secretin's powers/role?
Its core job is to raise duodenal pH by prompting the pancreas and liver to release bicarbonate-rich fluid that neutralizes incoming acidic chyme. It also fine-tunes water homeostasis and dampens gastric acid secretion.
Who discovered Secretin?
William Bayliss and Ernest Starling isolated its action in 1902 and coined the name 'secretin' because it caused the pancreas to secrete its digestive juice. Their experiment is widely regarded as the founding moment of the hormone concept.
Why is Secretin important?
Without it, acidic stomach contents would erode the duodenal lining and inactivate pancreatic enzymes, collapsing the entire digestive cascade. It also contributes to osmoregulation and food-intake signaling, linking digestion to systemic water balance.
How does Secretin's story end?
After entering the bloodstream, it reaches the pancreas, liver, and stomach to trigger bicarbonate and water secretion, then is quickly cleaved by circulating peptidases. This rapid degradation keeps the signal tightly matched to the meal that prompted its release.
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