Haustral churning, Gastrocolic reflex and mass peristalsis & Defecation

• As the cecum becomes filled and distends, a local reflex causes: • Closure of the ileocecal valve. • Activation of haustral churning. • Haustral churning mixes the chyme, which helps absorption of water, salts, and vitamins. • Haustral churning propels the contents of the colon along the large intestine. • The gastrocolic reflex is also triggered when food enters and distends the stomach. • This reflex intensifies strong mass peristalsis movements that force feces into the rectum • The defecation reflex is activated by stretch receptors stimulated by the filling of the rectum. • Defecation is an ANS reflex in which sensory impulses are sent to the control center in the spinal cord. • Parasympathetic impulses travel down the spinal sacral nerves and: • Stimulate longitudinal contractions of the rectum forcing feces into the anal canal. • Relax the internal anal sphincter allowing the feces to move toward the external anal sphincter. • Voluntary relaxation of the external anal sphincter allows defecation to be completed.

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