The migrating motor complex (MMC) serves as the 'housekeeper' of the gut. Phase III of the MMC is characterised by which features?

• A Regular burst of intense propagating contractions sweeping from the stomach to the terminal ileum, occurring every 90–120 minutes during fasting, mediated primarily by motilin released from M cells of the upper GI tract ✓
• B Irregular contractile activity corresponding to the fed state, driven by GLP-1 and peptide YY
• C Phase III occurs postprandially and is initiated by CCK release from the duodenum
• D Phase III consists of quiescent smooth muscle activity allowing mucosal recovery between eating episodes

Explanation

The MMC is a cyclically recurring pattern of gut motility during fasting, consisting of 3–4 phases: Phase I (quiescence, 45–60 min), Phase II (irregular contractions), and Phase III (activity front, 5–15 min) — a burst of regular, intense propagating contractions beginning in the gastric antrum and sweeping to the terminal ileum, propelling undigested residue and bacteria distally. The MMC repeats every 90–120 minutes. Motilin, released from M cells (enterochromaffin-like cells in the upper gut) in a cyclic, fasting-driven pattern, is the primary initiator of Phase III in the stomach. Erythromycin acts as a motilin agonist and mimics Phase III. Feeding abolishes the MMC and switches to the fed motor pattern (option B). Options C and D are incorrect.

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

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