The migrating motor complex (MMC) in the fasting state has a cycle of approximately 90 minutes and is divided into four phases. Phase III (activity front) is primarily regulated by which peptide hormone?
- A Cholecystokinin (CCK), released postprandially; suppresses phase III and initiates phase I (quiescence)
- B Gastrin, released by G cells in antrum; initiates activity front by acting on gastrin receptors on interstitial cells of Cajal
- C Secretin, released by S cells in duodenum in response to acid; triggers phase III by inhibiting motilin release
- D Motilin, released from M cells of the duodenum and jejunum; acts on motilin receptors (also the target of erythromycin) ✓
Explanation
The fasting MMC begins in the stomach and propagates aborally to the terminal ileum approximately every 90 minutes. Phase III (the 'housekeeper' contraction wave) is initiated by motilin, a 22-amino-acid peptide secreted by enteroendocrine M cells of the proximal small intestine. Motilin plasma levels peak just before phase III begins. Erythromycin and other macrolides act as motilin receptor agonists and are used clinically as prokinetic agents. Food suppresses motilin secretion and MMC cycling, replacing it with the fed (segmentation) pattern. CCK is postprandial and inhibits phase III.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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