Question

What is the function of secretin?

Answer 1

Hint: The activities of the gastro-intestinal tract are under neural and hormonal control for proper coordination of different parts. The sight, smell and/or the presence of food in the oral cavity can stimulate the secretion of saliva. The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS.

Complete answer:
Hormonal control of the secretion of digestive juices is carried out by the local hormones produced by the gastric and intestinal mucosa. Some of the major hormones are:
(i) Gastrin- Its source of secretion is the stomach and the target organ is also the stomach, its action is to stimulate the gastric gland to secrete and release gastric juice.
(ii) Enterogastrone- It is also known as Gastric inhibitory peptide or GIP. Its source of secretion is duodenum and the organ of target is the stomach. It inhibits gastric secretion and motility i.e., slows gastric motility.
(iii) Secretin- It was the first hormone discovered by scientists. The source of secretion is duodenum and it acts on the pancreas, liver and stomach. Its function is to release bicarbonates in the pancreatic juice. It increases secretion of bile and decreases gastric secretion and motility.
(iv) Cholecystokinin-pancreazymin (CCK-PZ)- It is released by the small intestine and acts on the gallbladder and pancreas. It contracts the gallbladder to release bile. Stimulates pancreas to secrete and release digestive enzymes in the pancreatic juice.
(v) Enterocrinin- It acts on the small intestine to stimulate the Crypts of Lieberkuhn to release enzymes into the intestinal juice.
(vi) Vasoactive Intestinal Peptide (VIP) - It acts on the small intestine and stomach to dilate the peripheral blood vessels of the gut. It also inhibits gastric acid secretion.
(vii) Somatostatin (SS) - It is released from the Delta cells of islets of Langerhans of the pancreas. It acts on the pancreas and gastrointestinal tract. It inhibits the secretion of glucagon by alpha cells and insulin by beta cells. It also inhibits absorption of nutrients from the gastrointestinal tract. Argentaffin cells of gastric glands also secrete this hormone where it suppresses the release of hormones from the digestive tract.

Note:
Duocrinin is a hormone that is secreted by duodenum and acts on duodenum. Its function is to stimulate the Brunner’s glands to release mucus and enzymes into intestinal juice. Pancreatic Polypeptide (PP) acts on pancreas and inhibits the release of pancreatic juice from the pancreas.