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The anus is the site of potential infections and other conditions, including cancer (see anal cancer). [4] With anal sex, the anus can play a role in sexuality. Attitudes toward anal sex vary, and it is illegal in some countries. [5] The anus is often considered a taboo part of the body, [5] and is known by many, usually vulgar, slang terms.
The external anal sphincter is far more substantial than the internal anal sphincter. The proximal portion of external anal sphincter overlaps the internal anal sphincter (which terminates distally a little distance proximal to the anal orifice) superficially; where the two overlap, they are separated by the intervening conjoint longitudinal muscle.
The rectum receives fecal material from the descending colon, transmitted through regular muscle contractions called peristalsis. [11] 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 pass feces, a process called defecation. [11]
The canal is differentiated from the rectum by a transition along the internal surface from endodermal to skin-like ectodermal tissue. The anal canal is traditionally divided into two segments, upper and lower, separated by the pectinate line (also known as the dentate line): upper zone (zona columnaris) mucosa is lined by simple columnar ...
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal.It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum.
The final branch which is important for the digestive system is the inferior mesenteric artery, which supplies the regions of the digestive tract derived from the hindgut, which includes the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, and the anus above the pectinate line.
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.
In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. [1] In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a function. Tissues of different types combine to form an organ which has a specific ...