Physiology, Gastrocolic Reflex

Excerpt

The gastrocolic reflex is a physiological reflex that controls the motility of the lower gastrointestinal tract following a meal. As a result of the gastrocolic reflex, the colon has increased motility in response to the stretch of the stomach with the ingestion of food. The gastrocolic reflex allows room for the consumption of more food via control over peristalsis and movement of ingested food distally toward the rectum. Myoelectric recordings demonstrate the reflex in the large intestine that shows a spike in electrical activity within minutes of food consumption. The gastrocolic reflex initiates and controls migrating motor complexes throughout the colon. These motor complexes act cyclically during the digestion process and can be broken up into four phases.

The control of these phases is multifactorial, involving neurological, mechanical, and paracrine mediators. Several neuropeptides are suspected mediators of the reflex, including cholecystokinin, serotonin, neurotensin, and gastrin. Three centers of control have been identified and studied and include myogenic control, hormonal control, and neural control. The sigmoid colon is the region most affected during the phasic response of digestion, which consists of cyclical periods of contraction followed by relaxation to propel food distally toward the rectum. These contractions are generated in the myenteric plexus and accomplished by the muscularis externa — the gastrocolic reflex results in the urge to defecate after a meal. When food enters the rectum and drives pressures up, the gastrocolic reflex stimulates expulsion of the contents of the rectum via defecation.