![]() ![]() These are exquisitely painful, with pain occurring after a motion is passed other symptoms may include minor bleeding, discharge, or itch. The pectinate line, which separates the internal from the external anus, can be seen.Īnal fissures are tears in the external lining of the lining (mucosa) of the anus. Relaxation of the internal and external anal sphincters allows the feces to exit from the anus, finally, as the levator ani muscles pull the anus up over the exiting feces.Ĭlinical significance Image of the anus affected by hemorrhoids. The rectum shortens as feces are pushed into the anal canal and peristaltic waves push the feces out of the rectum. The internal anal sphincter (an involuntary muscle) responds to the pressure by relaxing, thus allowing the feces to enter the canal. Contractions of abdominal and pelvic floor muscles can create intra-abdominal pressure, which further increases intra-rectal pressure. Intra-rectal pressure builds as the rectum fills with feces, pushing the feces against the walls of the anal canal. In some genetic populations, androgenic hair is less common. Although initially sparse, it fills out by the end of puberty, if not earlier. : 285 Developmentĭuring puberty, as testosterone triggers androgenic hair growth on the body, pubic hair begins to appear around the anus. The stratified squamous epithelium gradually accumulates sebaceous and apocrine glands. The pseudostratified columnar epithelium of the gastrointestinal tract transitions to stratified squamous epithelium at the pectinate line. ![]() The anus receives blood from the inferior rectal artery and innervation from the inferior rectal nerves, which branch from the pudendal nerve. : 397 The pectinate line is also the division between the internal and external anus. Below this point, the mucosa of the internal anus becomes skin. This represents the point of transition between the hindgut and the ectoderm in the embryo. The anus is surrounded in its length by folds called anal valves, which converge at a line known as the pectinate line. The top and bottom of the anus are surrounded by the internal and external anal sphincters, two muscular rings which control defecation. The anus passes through the pelvic floor. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum. Some sexually transmitted infections including HIV/AIDS and anal warts can be spread via anal sex. The anus is often considered a taboo part of the body, and is known by many, usually vulgar, slang terms. Attitudes toward anal sex vary, and it is illegal in some countries. With anal sex, the anus can play a role in sexuality. The anus is the site of potential infections and other conditions, including cancer (see anal cancer). In part owing to its exposure to feces, a number of medical conditions may affect the anus, such as hemorrhoids. It is located behind the perineum which is located behind the vulva or scrotum. The inner sphincter is involuntary and the outer is voluntary. These are the internal anal sphincter and the external anal sphincter, which are circular muscles that normally maintain constriction of the orifice and which relaxes as required by normal physiological functioning. Two sphincters control the exit of feces from the body during an act of defecation, which is the primary function of the anus. In humans, the anus ( PL: anuses or ani from Latin ānus, "ring", "circle") is the external opening of the rectum, located inside the intergluteal cleft and separated from the genitals by the perineum. ![]()
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