The rectum is a muscular tube about
5 in. (12.7 cm) long that is at
the end of the large intestine (colon). The rectum connects the colon to the
anus, which is the opening where stool exits the body.
internal and external anal sphincters are rings of muscle at the opening of the
anus. The sphincters keep the anus closed as stool collects in the rectum.
Eventually the pressure on the rectum wall causes the internal anal sphincter
to relax. Conscious control over the external anal sphincter allows stool to
pass out of the body through the anus.