Migrating Motor Complex (MMC)

• The migrating motor complex (MMC) is a cyclical, recurring pattern of distinct motor activity in the gastrointestinal (GI) tract that occurs in the fasted state

Phases of the Migrating Motor Complex

• Phase I (quiescent period): Characterized by the absence of contractile activity
• Phase II (period of increasing activity): Random, intermittent contractions occur
• Phase III (period of peak activity): A burst of intense, repetitive contractions that propagate aborally
• Phase IV (period of declining activity): A short transition period between phase III and phase I of the next cycle
• Each MMC cycle lasts approximately 90-120 minutes
• The MMC starts in the stomach or small intestine and propagates distally
• The MMC is regulated by both neural and hormonal factors

Functions of the Migrating Motor Complex

• Housekeeping function: sweeps undigested material, cellular debris, and bacteria from the stomach and small intestine into the colon, preventing bacterial overgrowth in the upper GI tract
• Prevents stasis: reduces the risk of bacterial overgrowth and subsequent inflammation or infection
• Stimulates gallbladder contraction and pancreatic secretion: helps to deliver bile and pancreatic enzymes to the small intestine in preparation for the next meal
• MMCs are inhibited by feeding

Regulation of the Migrating Motor Complex

• Neural control: enteric nervous system (ENS) plays a crucial role
  • Motilin: a peptide hormone secreted by enteroendocrine cells in the small intestine, is a primary regulator of the MMC
  • Motilin stimulates contraction of gastric and intestinal smooth muscle, promoting the initiation and propagation of phase III
• Hormonal control: several hormones, including ghrelin, insulin, and somatostatin, have effects on the MMC
  • Ghrelin stimulates MMC activity
  • Insulin and somatostatin inhibit MMC activity

Clinical Significance of the Migrating Motor Complex

• Disturbances in MMC activity have been implicated in several GI disorders
• Small intestinal bacterial overgrowth (SIBO): impaired MMC can lead to bacterial overgrowth in the small intestine
• Gastroparesis: delayed gastric emptying, can be associated with abnormal MMC activity in the stomach
• Irritable bowel syndrome (IBS): some patients with IBS exhibit altered MMC patterns, which may contribute to their symptoms
• Postoperative ileus: temporary paralysis of the GI tract, which can disrupt MMC activity and delay recovery of bowel function after surgery
• Medications: certain drugs, such as opioids and anticholinergics, can inhibit MMC activity and contribute to GI dysfunction

Motilin Receptor Agonists

• Used to treat gastroparesis and constipation by stimulating gastric emptying and intestinal motility
• Erythromycin is a macrolide antibiotic that acts as a motilin receptor agonist
• Can be used to improve gastric emptying in patients with gastroparesis or to stimulate bowel movements in patients with constipation

Factors that Disrupt the Migrating Motor Complex

• Neurological disorders: can disrupt the autonomic nervous system and affect MMC activity
• Surgical procedures: can cause postoperative ileus and disrupt MMC activity
• Medications: Opioids, anticholinergics, and other drugs can inhibit MMC activity
• Stress and psychological factors: can influence MMC activity via the brain-gut axis
• Medical conditions: such as diabetes mellitus and hypothyroidism, can affect MMC activity