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The human rectum is a part of the lower gastrointestinal tract. The rectum is a continuation of the sigmoid colon, and connects to the anus. The rectum follows the shape of the sacrum and ends in an expanded section called an ampulla where feces is stored before its release via the anal canal.
Anatomy of the human anus. Frontal section. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum, passing through the pelvic floor. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation.
The anal verge refers to the distal end of the anal canal, a transitional zone between the epithelium of the anal canal and the perianal skin. It should not be confused with the pectinate line between the upper and lower zones within the anal canal. The anal gland secretes lymphal discharge and built-up fecal matter from the colon lining.
Anal columns (Columns of Morgagni or less commonly Morgagni's columns) are a number of vertical folds, produced by an infolding of the mucous membrane and some of the muscular tissue in the upper half of the lumen of the anal canal. They are named after Giovanni Battista Morgagni, who has several other eponyms named after him.
The pelvic cavity also contains major arteries, veins, muscles, and nerves. These structures coexist in a crowded space, and disorders of one pelvic component may impact upon another; for example, constipation may overload the rectum and compress the urinary bladder, or childbirth might damage the pudendal nerves and later lead to anal weakness.
The combining forms reflect the rectum (recto-, -rectal) and uterus (utero-, -uterine). In Obstetrics and gynaecology, it is commonly referred to as the pouch of Douglas or the posterior cul-de-sac. [7] The Douglas fold (rectouterine plica), Douglas line, and Douglas septum are likewise named after the same James Douglas.
The external anal sphincter (or sphincter ani externus) is an oval tube of skeletal muscle fibers. [1] Distally, it is adherent to the skin surrounding the margin of the anus . [ 2 ] It exhibits a resting state of tonical contraction [ 1 ] and also contracts during the bulbospongiosus reflex .
The rectococcygeal muscles are composed of smooth muscle and run from the anterior surface of the 2nd and 3rd coccygeal vertebrae down the posterior wall of the rectum as a triangular shaped muscle before branching and inserting among the various muscles and fascial structures associated with the pelvic diaphragm and anal canal and collectively called longitudinal anal muscles.