Peristalsis: The Coordinated Wave That Moves Gut Contents

Peristalsis is the involuntary, rhythmic contraction of smooth muscle in the gastrointestinal tract that propels contents forward.

Mechanism

• Circular muscle contraction behind bolus → narrows lumen.
• Longitudinal muscle contraction ahead → shortens segment, pulls tube forward.
• Coordinated by enteric nervous system (myenteric plexus) and modulated by autonomic input.
• Pacemaker activity: interstitial cells of Cajal (ICC) generate slow waves.

Regional Patterns

• Esophagus: Primary peristalsis (swallow-initiated) + secondary (distension-triggered).
• Stomach: 3/min slow waves; peristalsis mixes and grinds, pushes chyme through pylorus.
• Small intestine: Segmenting contractions (mixing) + migrating motor complex (MMC) fasting cleansing waves.
• Colon: Haustral shuffling, mass movements (1–3/day) → defecation urge.

Clinical Relevance

• Ileus: absent peristalsis (post-op, electrolyte imbalance, opioids).
• Diarrhea: exaggerated peristalsis + secretion.
• Constipation: reduced frequency/strength.
• Achalasia: failed LES relaxation + absent esophageal peristalsis.