Mass movements, mainly stimulated by the gastrocolic reflex, push the feces into the rectum, which is usually empty.

Distension of the rectum stimulates the defecation reflex .

• Largely a spinal reflex mediated via the pelvic nerves, and results in reflex relaxation of the internal anal sphincter followed by voluntary relaxation of the external anal sphincter and defecation.

• In humans, defecation can be prevented by voluntary constriction of the external sphincter. When this happens, the rectum soon relaxes and the internal sphincter again contracts, a state which persists until another bolus of feces is forced into the rectum.