Cholecystokinin

CHOLECYSTOKININ (CCK)
  • CCK is synthesized and released by enteroendocrine cells in the mucosal lining of the small intestine (mostly in the duodenum and jejunum), called I cells, neurons of the enteric nervous system, and neurons in the brain.
  • It is released rapidly into the circulation in response to a meal. The greatest stimulator of CCK release is the presence of fatty acids and/or certain amino acids in the chyme entering the duodenum.
FUNCTIONS OF CHOLECYSTOKININ
Digestion

  • CCK mediates digestion in the small intestine by inhibiting gastric emptying. It stimulates the acinar cells of the pancreas to release a juice rich in pancreatic digestive enzymes that catalyze the digestion of fat, protein, and carbohydrates. Thus, as the levels of the substances that stimulated the release of CCK drop, the concentration of the hormone drops as well.
  1. The release of CCK is also inhibited by somatostatin and pancreatic peptide. Trypsin, a protease released by pancreatic acinar cells, hydrolyzes CCK-releasing peptide and monitor peptide, in effect turning off the additional signals to secrete CCK.
  • CCK also causes the increased production of hepatic bile, and stimulates the contraction of the gall bladder and the relaxation of the sphincter of Oddi (Glisson's sphincter), resulting in the delivery of bile into the duodenal part of the small intestine.
  • Enhances small intestinal & colonic motility. 
Satiety
  • CCK mediates satiety by acting on the CCK receptors distributed widely throughout the central nervous system. The mechanism for hunger suppression is thought to be a decrease in the rate of gastric emptying
Exam Question
  • Cholecystokinin is produced from Duodenal mucosa.
  • Release of Cholecystokinin leads to an increase in the secretion of pancreatic enzymes into the small intestine.
  • Gstric emptying is decreased by Cholecystokinin.
  • Cholecystokinin leads to contraction of gall bladder.
  • Cholecystokinin lead to secretion of pancreatic juice rich in enzymes.
  • Cholecystokinin increases small intestinal peristalsis.

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