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Gastrointestinal Hormones

A. Classification : The GI peptides can be classified as below :

  1. Gastrin family : The primary hormones in this group are gastrin and cholecystokinin (CCK)
  2. Secretin family : The primary hormones in this group are secretin, glucagon, glicentin (GLI), VIP, and gastrin inhibitory peptide (GIP).
  3. Others : Many of the GI peptides do not belong to the above two groups e.g. somatostatin, motilin, substance P, guanylin, neuropeptide YY etc.

B. The GI cells secreting the GI peptides can be classified as Enterochromaffin (or ECL)cells :

These cells secrete serotonin also (in addtion to secreting polypeptides)


2. APUD (or amine precursor uptake and decarboxylase) cells : These cells secrete amines also (in addition to secreting polypeptides). Apart from the GIT, APUD cells can also be found in other organs e.g. lungs.  Carcinoid tumors arise from APUD cells.


The important GI hormones are discussed below :

Gastro – Intestinal Hormones







Micro and macro heterogenecity

Micro and heterogencity

Only one from



G – cells, antrum

I – cells – Upper SI

S cells – upper SI

K cells – upper S1


Stimulates acid and pepsin; stimulates gastric motility; stimulates insulin; stimulates glucagons; closure of G-E

Stimulates GB; relaxes sphincter of Oddi; stimulates pancreatic juice (rich in enzymes); inhibits gastric emptying; may stimulate pyloric sphincter; stimulates insulin and glucagons; trophic to pancreas; increases enterokinase; may increase motility of SI and colon; augments secretion

Stimulates secretion of pancreatic juice (alkaline); inhibits gastric acid secretion; may stimulate pyloric A1 sphincter; stimulates insulin; augments CCK; action of secretion is to decrease H+ in SI

In large dose it inhibits gastric motility and inhibits gastric secretion; stimulates insulin


Increased by: peptides, distension, vagus, cold, epinephrine decreased by calcitonin, acid, somatostatin, secretion, GIP, VIP

Increased by peptides, aminoacids, fatty acids (not triglycerides)

Increased by products of food digestion, acid in duodenum

Increased by fatty acids, amino acids, glucose







D cells of GIT

EC cells duodenum

Nerve in ileum

Stimulates intestinal secretion of electrolytes and water; relaxation of intestinal smooth muscle; dilation of peripheral blood vessels; inhibits gastric acid secretion – stimulated gastric acid secretion; potentiates action of acetylcholine on salivary glands; stimulates pancreatic bicarbonate secretion and inhibits H secretion

Inhibits secretion of gastrin, VIP, GIP, secretion, motilin; inhibits pancreatic exocrine secretion; inhibits gastric secretion and motility; inhibits gall bladder contraction; inhibits absorption of aminoacids, triglycerides, Increased by acid in lumen; decreased by vagus

Contraction of intestinal smooth muscle; regulator of MMC (migrating motor complex)

Inhibits gastrointestinal motility; increase ileal blood flow

Increased by fat in jejunum

Increased by acid in lumen decreased by vagus




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