Expansion
Cyclical waves of contraction every 90 to 120 minutes between meals
Expansion
Occurs only in the fasting state, in cycles of 90 to 120 minutes, with four phases:
- Phase I: quiescence, about half the cycle
- Phase II: irregular contractions
- Phase III: intense regular contractions sweeping from stomach to terminal ileum, lasting 5 to 10 minutes
- Phase IV: brief transition
Driven by motilin, released cyclically from duodenal M cells, and abolished by eating, which switches the gut to the fed pattern.
Functions:
- Clears indigestible residue too large to empty during the fed state
- Sweeps bacteria distally, limiting small bowel colonisation
- Prevents stagnation
Loss of the complex, as in diabetic autonomic neuropathy, scleroderma, opioid use or after surgery, allows small intestinal bacterial overgrowth, with bloating, malabsorption and B12 deficiency.
Erythromycin is a motilin receptor agonist, which is why it is used as a prokinetic and why it can cause abdominal cramps.