Cholecystokinin (CCK) is released from I-cells of the duodenum in response to fat and protein. CCK inhibits gastric emptying primarily through which mechanism involving the enteric nervous system?

• A CCK directly activates the pyloric sphincter smooth muscle via CCK-A receptors on smooth muscle
• B CCK acts on vagal afferent CCK-A receptors, which trigger a vago-vagal reflex causing pyloric contraction and reduced antral motility ✓
• C CCK inhibits secretin release, reducing bicarbonate secretion and indirectly slowing gastric emptying
• D CCK stimulates somatostatin from D-cells, which then suppresses antral gastrin and gastric motility

Explanation

The primary mechanism of CCK-induced delayed gastric emptying is neural rather than hormonal: CCK acts on CCK-A receptors on vagal afferent neurons in the intestinal wall, activating a vago-vagal reflex arc. The efferent limb involves vagal cholinergic neurons activating enteric inhibitory neurons in the pyloric region, causing pyloric contraction (pylorospasm) and inhibition of antral peristalsis. This is why the effect is rapid (seconds) rather than the delayed onset expected of a circulating hormonal effect. CCK-A receptor antagonists abolish the intestinal brake response.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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