Main Page | See live article | Alphabetical index The rectum is the final portion of the large intestine in some mammals, and the gut in others, terminating in the anus. Table of contents 1 The rectum in human defecation 2 Muscular anatomy of the human pelvis and rectum 3 Anal sex The rectum in human defecation The rectum acts as a temporary storage facility for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed. If defecation is delayed for a prolonged period constipation and hardened feces results. When the rectum is full the increase in intrarectal pressure forces the walls of the anal canal apart allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincters of the anus allow the feces to be passed by muscles pulling the anus up over the exiting feces. See defecation for a fuller treatment. Muscular anatomy of the human pelvis and rectum The Levatores ani constrict the lower end of the rectum and vagina. They elevate and invert the lower end of the rectum after it has been protruded and everted during the expulsion of the feces. They are also muscles of forced expiration. The Coccygei pull forward and support the coccyx, after it has been pressed backward during defecation or parturition. The Levatores ani and Coccygei together form a muscular diaphragm which supports the pelvic viscera. Anal sex Anal sex or anal intercourse is human sexual behavior involving the anus and rectum, especially the insertion of the erect penis into the rectum via the anus. See also: Gastrointestinal tract This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.