GASTRO-INTESTINAL MUCOSA -
It develops from the endoderm of the embryo.
Inner most layer of the wall of the alimentary canal is called mucosa. Certain cells of the mucosa of the stomach and intestine secrete important hormones.
(a) STOMACH. The mucosa of the pyloric region of the stomach synthesizes, stores and secretes the hormone gastrin. This hormone stimulates the secretion of gastric juice and movements of the stomach.
(b) INTESTINE. It secretes the following hormones.
(i) Secretin. It is secreted by the intestinal mucosa of duodenum and jejunum. It causes the release of water and sodium bicarbonate from the pancreas in the pancreatic juice and from the liver in the bile. Secretin also inhibits the secretion and movements of the stomach. Secretin was the first hormone discovered by Bayliss & Sturling.
(ii) Cholecystokinin-pancreozymin (CCK-PZ). This hormone is secreted by the mucosa of entire small intestine. The actions of cholecystokinin and pancreozymin were discovered independently.
This hormone stimulates the gall bladder to release the bile and also stimulates the pancreas to release its enzymes.
(iii) Enterogastrine (= Gastric Inhibitory Peptide-GIP). It is secreted by duodenal mucosa that inhibits gastric secretion and contractions.
(iv) Duocrinin. This hormone is also secreted by duodenal mucosa. It stimulates the Brunner's glands to release mucus and a few enzymes into the intestinal juice.
(v) Enterocrinin. It is also secreted by duodenal mucosa. It stimulates the crypts of Lieberkuhn to secrete the enzymes in the intestinal juice.
(vi) Vasoactive Intestinal Peptide (VIP). It is secreted by the small intestine. It dilates peripheral blood vessels of the small intestine and inhibits gastric acid secretion.
(vii) Villicrinin. It is secreted by the mucosa of entire small instestine. It accelerates the movement of intestinal villi to facilitate the absorption of food in the small intestine.