Gastro Intestinal hormones
Gastro-Intestinal Tract is the largest endocrine organ by it’s size but not defined as endocrine gland. Diffused distribution of entero-endocrine cells through out GIT is present-
- Endocrine cells decrease progressively towards the colon
- Enterochromaffin cells contain 5-OH tryptophan (Serotonin)
- GI hormones show both endocrine and paracrine activities
There are no feed back regulation for Gastro Intestinal hormones hormones. Presence of food or GIT environment stimulates their secretion and Removal of the stimulus stops secretion.
There are several polypeptide substances synthesized and secreted by cells of GI tract. These include gastrin, secretin, cholecystokinin (CCK) or (pancreozymin), gastric inhibitory peptide(GIP), motilin, vasoactive intestinal polypeptide (VIP), somatostatin, bombesin and substance P.
Some of these hormones act as paracrine hormones; others enter circulation and act as general hormones. Many of these hormones are also found in the nervous system.
Based on structural and functional similarity, GI tract hormones are grouped into two families-
- Gastrin family – gastrin, CCK
- Secretin family – secretin, glucagon, glycentin, VIP, GIP
| Hormone | Site of production | Stimulus for release | Action |
| Gastrin | Distal stomach G cells | Protein in stomach, high gastric pH, vagal stimulus | Stimulates HCl, Pepsinogen secretions, gastric motility, growth of stomach epithelium |
| Secretin | Duodenum S cells | Acid in duodenum | Stimulates NaHCO3 secretion of bile and pancreas, inhibits GI motility and gastric secretions |
| CCK | Duodenum to Ileum. Also found in brain; CCK 8, 16 & 32. | Protein and fat in small intestine | Stimulates enzyme secretions of pancreas and gall bladder contraction, inhibits gastric emptying |
| GIP | Duodenum and upper jejunum | Carbohydrates and fat in small intestine | Stimulates pancreatic insulin secretion, inhibits gastric motility and secretion |
| Motilin | Duodenum and jejunum K cells | Acetylcholine | Regulates gastric motility between meals, tone of lower esophageal sphincter |