Hormone

Source

Chemistry

Physiological stimulus for release

Action

1. Gastrins

Antral mucosa and duodenal bulb

Polypeptides consisting of G14, G17, G34 and a big gastrin with 45 amino acid residues (in both sulfated and non-sulfated forms)

Protein breakdown products distension of stomach, vagal stimulation of Calcium, Epinephrine

Gastric acid, pepsins and intrinsic factor stimulation.

Increases growth of gastric mucosa Stimulation of gastric motility.

Closure of gastro-oesophageal junction.

Stimulates glucagon secretion.

2. Cholecystokinin pancreozymin (CCK-PZ or CCK)

Mucosa of the upper small intestine and nerves of the distal part of ileum and colon

Polypeptides with 39 amino acids. Also present in various forms (structure resembles gastrins)

Secretin products of protein digestion soaps and fats

Secretion of enzyme rich pancreatic juice.

Trophic action on pancreas.

Contraction of gall bladder.

Relaxation of sphincter of Oddi.

Inhibits gastric emptying and prevents regurgitation of duodenal contents into the stomach.

Stimulates glucagon secretion.

3. Secretin

Cells present in the deep-seated glands from the upper intestine

Linear polypeptide structure similar to glucagon, glicentin (GLI) VIP, GIP

Acid chyme in duodenum, vagal stimulation products or protein digestion.

Copious bicarbonate rich pancreatic juice secretion.

Increase bile secretion. (Choleretics) decreases gastric acid secretion.

Causes contraction of pyloric. sphincter.

Augments cholecystokinin action.

4. Somatostatin

Gastrointestinal mucosa

14 amino acid residues with disulphide bridge

-----

Inhibits gastric secretion

5. VIP (Vasoactive Intestinal peptide)

Gland cells and nerves of the Gl tract

28 amino acid residues

-----

Stimulates intestinal secretion of water and electrolytes.

Inhibits gastric acid secretion.

Potentiates the action of acetylcholine on salivary glands

6. Enterogastrone

-do-

-do

Fats & fatty acids secretion.

Inhibition of gastric secretion

7. Substance P

Endocrine cells of the GI tract

11 amino acid residues

----

Stimulates intestinal motility

8. Motilin

Duodenal mucosa

22 amino acid residues

----

Stimulates gastric acid secretion

9. Glucagon

(Intestinal glucagon)

A' cells of the mucosa of stomach and duodenum

29 amino acid residues

----

Plays a role in hyperglycemia of diabetes

Functions in GIT are not known.

10. Glicantin

(glucagon like immunoreactivity GLI)

-do-

Larger molecule than glucagon

----

Exact mode of action in GIT is not known

11. Villikinin

Acid chyme in the intestine

Movements of the villi

12. Enterocrinin

Mechanical distension of small intestine presence of food

Increases secretion of intestinal enzymes and sulcus entericus