Question

Describe how pancreatic exocrine secretion is regulated by secretin and CCK (site of secretion, stimuli, and actions of secretin and CCK).

Answer 1

Answer) pancreatic exocrine secretion is pancreatic juice and pancreatic enzymes by the secretory acinar cells and duct cells of exocrine portion of pancreas.

It is regulated by secretin and CCK.

Site of secretion of secretin and cholecystokinin(CCK) -

Secretin - It is secreted by argentaffin ( or S) cells in the crypts of the mucosa of upper part of the small intestine i.e duodenum and jejunum.

It is secreted as prosecretin(inactive) which gets activated into secretin(active form) in presence of gastric hydrochloric acid.

Cholecystokinin-It is produced by granular mucosal cells of upper part of small intestine i.e duodenum and jejunum.

STIMULI for secretion-

Factors which increase secretin and Cholecystokinin(CCK) release are-

1)Acid in the duodenum causes more secretin liberation and feeble stimulation of CCK.

2)Products of Carbohydrates, fats and protein digestion in the small intestine(specially peptides, amino acids are major stimuli) cause more CCK release.

ACTIONS-

Secretin -

It acts on the duct cell of the pancreas and stimulates the secretions of water and bicarbonates of the pancreatic juice to produce alkaline watery pancreatic juice.

It also stimulates bile secretion and potentiates the effect of CCK on the pancreas.

It along with CCK causes the contraction of pyloric sphincter of stomach and delays gastric emptying. Thus, preventing the reflux of duodenal contents into the stomach.

Cholecystokinin -

-It causes contraction of gall bladder to release bile and also causes secretion of pancreatic juice rich in pancreatic enzymes by causing discharge of zymogen granules from the pancreatic acinar cells.

-It also increases the secretion of enterokinase from the duodenum and may also increase the motility of small and large intestine.

-It produces increased growth effect on pancreas.

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