Secretin at a glance
| Feature | What researchers understand |
|---|---|
| Peptide length | 27 amino acids |
| Main source | S cells in the duodenum and upper small intestine |
| Primary trigger | Acidic stomach contents entering the duodenum |
| Main target | Pancreatic and bile duct cells |
| Key action | Stimulates bicarbonate-rich fluid to neutralise acid |
| Receptor type | Class B G protein-coupled receptor, or GPCR |
| Research areas | Digestion, fluid balance, gut–brain signalling and neurobiology |
Why was secretin historically important?
The problem: scientists could not explain how the intestine controlled the pancreas
At the beginning of the twentieth century, many researchers believed the nervous system controlled digestion almost entirely. Bayliss and Starling challenged this view in 1902 while studying pancreatic secretion.
They observed that acid placed in the intestine could cause the pancreas to release digestive fluid, even when normal nerve connections were not responsible for the response. They then prepared an extract from intestinal tissue and found that it could stimulate pancreatic activity when introduced into the bloodstream.
They named the substance secretin.
The solution: a new model of internal communication
Secretin showed that one organ could release a chemical messenger into the blood, which then travelled to another organ and changed its behaviour. This helped establish the modern endocrine concept.
Think of the body as a large construction site:
- The stomach delivers a load of acidic material.
- The duodenum acts as the site supervisor.
- Secretin is the urgent radio message.
- The pancreas and bile ducts receive the message and send alkaline bicarbonate to neutralise the load.
That discovery made secretin more than another digestive molecule. It helped create the scientific language used to describe hormones today.
Short summary: Secretin helped prove that the body communicates through chemical messages, not only nerves.
