TRUE about secretin includes all of the following EXCEPT (AIPG 2008)
|A||It increases the acidity of biliary and pancreatic secretions|
|B||It decreases gastric acid secretion|
|C||It decreases gastrin secretion and gastric emptying|
|D||Increases flow and velocity of bile|
1. Secretin occupies a unique position in the history of physiology. In 1902,Bayliss and Starling first demonstrated that the excitatory effect of duodenal stimulation on pancreatic secretion was due to a blood- borne factor. Their research led to the identification of secretin. They also suggested that many chemical agents might be secreted by cells in the body and pass in the circulation to affect organs some distance away. Starling introduced the term hormone to categorize such “chemical messengers.” Modern endocrinology is the proof of the correctness of this hypothesis.
2. Secretin is secreted by S cells that are located deep in the glands of the mucosa of the upper portion of the small intestine. The structure of secretin is different from that of CCK and gastrin but very similar to that of glucagons, GLI, VIP, and GIP. Only one form of secretin has been isolated, and the fragments of the molecule that have been tested to date are inactive. Its half-life is about 5 minutes, but little is known about its metabolism.
3. Secretin increases the secretion of bicarbonate by the duct cells of the pancreas and biliary tract. It thus causes the secretion of a watery, alkaline pancreatic juice .Its action on pancreatic duct cells is mediated via cAMP. It also augments the action of CCK in producing pancreatic secretion of digestive enzymes. It decreases gastric acid secretion and may cause contraction of the pyloric sphincter.
4. The secretion of secretin is increased by the products of protein digestion and by acid bathing the mucosa of the upper small intestine. The release of secretin by acid is another example of feedback control secretin causes alkaline pancreatic juice to flood into the duodenum, neutralizing the acid from the stomach and thus inhibiting further secretion of the hormone.