- The epithelium present in the alimentary canal secretes hormones.
- These hormones are carried by blood to the digestive glands which then release their digestive secretions (enzymes) for the digestion of food.
- Different hormones secreted in the GI tract are as follows:
- Gastrin:
- Source: It is secreted by the mucosa of pyloric stomach.
- Stimulus for secretion: Distension of stomach on food entry.
- Target organ: Stomach
- Action:
- It stimulates the secretion of gastric juice in the stomach.
- It constricts the cardiac sphincter.
- Enterogastrone:
- Source: It is secreted by the duodenal epithelium.
- Stimulus for secretion: Chyme entry into the duodenum
- Target organ: Stomach
- Action:
- It slows down gastric contractions to delay its emptying.
- It stops the secretion of gastric juice.
- Secretin:
- Source: Duodenal epithelium
- Stimulus for secretion: Acidic chyme entry into the duodenum.
- Target organ: Stomach, Pancreas and Liver
- Action:
- It inhibits the secretion of gastrin in stomach.
- It stimulates the release of sodium bicarbonate in pancreatic juice from the pancreas.
- It stimulates liver for the secretion of bile.
- Cholecystokinin (CCK) or Pancreozymin:
- Source: Duodenal epithelium
- Stimulus for secretion: Presence of fats in the duodenum.
- Target organ: Pancreas and Gall bladder
- Action:
- It stimulates the pancreas to release enzymes like amylase, lipase, trypsin etc. in pancreatic juice.
- It stimulates the release of stored bile from the gall bladder.
- Villikinin:
- Source: Intestinal epithelium
- Stimulus for secretion: Food in the small intestine
- Target organ: Small intestine
- Action:
- It accelerates the movement of villi to increase the flow of blood and lymph and to enhance absorption.
- Duocrinin:
- Source: Intestinal epithelium
- Stimulus for secretion: Acidic chyme in the small intestine
- Target organ: Small intestine
- Action:
- It stimulates Brunner’s glands for the secretin of viscous mucus so that duodenum is protected from the acidic digestive enzymes secreted by the stomach.
- Enterocrinin:
- Source: Intestinal epithelium
- Stimulus for secretion: Acidic chyme in the small intestine
- Target organ: Small intestine
- Action:
- It stimulates Crypts of Lieberkuhn to release a group of digestive enzymes called carhohydrases (amylase, proteases, and lipases) that bring about the complete digestion of food.