Hormones Controlling Digestion
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Direct answer
Four hormones do nearly all the endocrine regulation of the human gut, and NCERT names exactly these: gastrin, secreted by the gastric mucosa, stimulates the stomach to secrete hydrochloric acid and pepsinogen and strengthens its motility; secretin, released from the duodenal mucosa when acidic chyme arrives, makes the pancreas pour out water and bicarbonate while inhibiting gastric secretion; cholecystokinin (CCK) from the same region contracts the gall bladder to release bile and drives the pancreas to secrete its digestive enzymes; and gastric inhibitory peptide (GIP) slows gastric secretion and motility, braking the stomach as the duodenum fills. All four act as true hormones — released into blood, returning to their target glands — and secretin has the historical distinction of being the first hormone ever discovered, by Bayliss and Starling in 1902.
What you must remember
- Gastrin: source, gastric mucosa (G cells of the pyloric region); stimulus, food especially proteins; action, stimulates HCl and pepsinogen secretion and gastric motility.
- Secretin: source, duodenal mucosa; stimulus, acidic chyme entering the duodenum; action, stimulates release of water and bicarbonate-rich pancreatic juice and inhibits gastric acid.
- Cholecystokinin: source, duodenum and jejunum; stimulus, fats and proteins in chyme; action, contracts the gall bladder (bile release) and stimulates pancreatic enzyme secretion.
- GIP: source, duodenum; action, inhibits gastric secretion and motility — the name states the function.
- Endocrine mode: these hormones travel in blood to their targets (stomach, pancreas, gall bladder), unlike local paracrine or neural signals.
- Historical payload: secretin was the first hormone discovered (Bayliss and Starling, 1902), and the word "hormone" itself arose from that line of work — a viva-classic.
- Boundary: NCERT's list stops at four; extras like motilin and VIP belong to higher textbooks and are not expected.
Follow one fatty meal through the duodenum
Eat a plate of fried food and watch the sequence. In the stomach, protein and the arriving food trigger gastrin, which raises acid output so pepsin can work. When the acidic, fat-rich chyme squirts through the pylorus, three things happen almost together. The acid bathes the duodenal lining and secretin fires: the pancreas sends water and bicarbonate to neutralise the acid, protecting the duodenal wall and setting the right pH for pancreatic enzymes. Fats in the chyme release CCK: the gall bladder squeezes bile into the duodenum to emulsify the fat, while the pancreas exports its enzyme cocktail. As the duodenum fills, GIP reins in the stomach so chyme delivery matches duodenal processing capacity.
Notice the elegance: each hormone is triggered by the very condition it corrects. Acid stimulates the hormone that brings base; fat stimulates the hormone that brings the fat-handling secretions; duodenal distension stimulates the hormone that slows delivery. This negative-feedback grammar — stimulus, messenger, corrective secretion — is the template for endocrine questions throughout the syllabus, and the gut provides its cleanest demonstration.
How the exam frames it
The dominant question type is source-and-action matching, and the pair students shuffle most often is secretin versus CCK: secretin brings pancreatic water and bicarbonate, CCK brings pancreatic enzymes and bile. Anchor them by the stimulus — acid calls secretin, fat calls CCK. The second trap is direction: GIP inhibits the stomach; gastrin stimulates it; a statement swapping these is false on sight. Assertion items also recycle the "first hormone" credit — secretin, 1902, Bayliss and Starling — so carry that date-credit pair. Finally, remember all four act through blood on glands, which distinguishes them from the nervous reflexes of the gut in any "how is digestion coordinated" question.
Frequently asked questions
Which gut hormone stimulates hydrochloric acid secretion?
Gastrin, released from the gastric mucosa, mainly in response to protein-rich food.
What are the two main actions of cholecystokinin?
It contracts the gall bladder to release bile and stimulates the pancreas to secrete digestive enzymes.
Which hormone was the first ever discovered, and from where is it released?
Secretin, discovered by Bayliss and Starling in 1902, is released from the duodenal mucosa in response to acidic chyme.
How does secretin protect the duodenum?
It triggers a watery, bicarbonate-rich pancreatic secretion that neutralises the acidic chyme.
What does gastric inhibitory peptide do?
It inhibits gastric secretion and motility, slowing the stomach as the duodenum fills.