| Human anus | |
|---|---|
 A woman's anus, without pubic hair | |
 Scheme ofdigestive tract, with anus marked | |
| Details | |
| Precursor | Proctodeum |
| System | Alimentary |
| Artery | Inferior rectal artery |
| Vein | Inferior rectal vein |
| Nerve | Inferior rectal nerves,pudendal nerve |
| Lymph | Superficial inguinal lymph nodes |
| Identifiers | |
| Latin | anus |
| TA98 | A05.7.05.013 |
| TA2 | 3022 |
| FMA | 15711 |
| Anatomical terminology | |
 |
| Major parts of the |
| Gastrointestinal tract |
|---|
Inhumans, theanus (pl.:anuses orani; fromLatinānus, "ring", "circle")[1][2] is the external opening of therectum located inside theintergluteal cleft. Twosphincters control the exit offeces from the body during an act ofdefecation, which is the primary function of the anus. These are theinternal anal sphincter and theexternal anal sphincter, which are circularmuscles that normally maintain constriction of the orifice and which relax as required by normal physiological functioning. The inner sphincter is involuntary and the outer is voluntary. Above the anus is theperineum, which is also located beneath thevulva orscrotum.
In part owing to its exposure to feces, a number of medical conditions may affect the anus, such ashemorrhoids.[3] The anus is the site of potentialinfections and other conditions, includingcancer (seeanal cancer).[4]
Withanal sex, the anus can play a role insexuality. Attitudes toward anal sex vary, and it is illegal in some countries.[5] The anus is often considered ataboo part of the body,[5] and is known by many, usually vulgar,slang terms. Somesexually transmitted infections includingHIV/AIDS andanal warts can be spread via anal sex.
The anus is the final part of thegastrointestinal tract, and directly continues from therectum, passing through thepelvic floor. The top and bottom of the anus are surrounded by theinternal andexternal anal sphincters, two muscular rings which control defecation.[6]: 397 The anus is surrounded in its length by folds calledanal valves, which converge at a line known as thepectinate line. This represents the point of transition between thehindgut and theectoderm in the embryo. Below this point, the mucosa of the internal anus becomes skin.[6]: 397 The pectinate line is also the division between the internal and external anus.
The anus receives blood from theinferior rectal artery and innervation from theinferior rectal nerves, which branch from thepudendal nerve.[7]
The pseudostratified columnarepithelium of the gastrointestinal tract transitions to stratified squamous epithelium at the pectinate line. The stratified squamous epithelium gradually accumulatessebaceous andapocrine glands.[8]: 285
Duringpuberty, as testosterone triggersandrogenic hair growth on the body,pubic hair begins to appear around the anus. Although initially sparse, it fills out by the end of puberty, if not earlier. In some genetic populations, androgenic hair is less common.
Intra-rectal pressure builds as the rectum fills with feces, pushing the feces against the walls of theanal canal. Contractions of abdominal and pelvic floor muscles can create intra-abdominal pressure, which further increases intra-rectal pressure. The internal anal sphincter (an involuntary muscle) responds to the pressure by relaxing, thus allowing the feces to enter the canal. The rectum shortens as feces are pushed into the anal canal andperistaltic waves push the feces out of the rectum. Relaxation of the internal and external anal sphincters allows the feces to exit from the anus, finally, as thelevator ani muscles pull the anus up over the exiting feces.
Anal fissures are tears in the external lining of the lining (mucosa) of the anus. These are exquisitely painful, with pain occurring after a motion is passed; other symptoms may include minor bleeding, discharge, or itch.[9] Generally, fissures are due to injury to the mucosa, or because of a poor local blood supply that prevents proper healing, with spasm of the external anal sphincter contributing.[9] The external anal sphincter can be relaxed by the application ofglyceryl trinitrate creams, andconstipation is managed withlaxatives and improving hydration.[9] Some fissures may requirebotulinum toxin injection; worst cases may require surgical intervention, such as "lateral internalanal sphincterotomy or advancement anoplasty"[clarification needed].[9]
Hemorrhoids are visible blood vessels from the internal or externalvenous plexuses of the anus. Haemorrhoids may; cause bleeding after passing a motion; be painful; cause an itch; orprolapse out of the anus.[9] Haemorrhoids are often associated with straining due to constipation, andpregnancy.[9] Usually, haemorrhoids are managed with medications tomake motions more soft and prevent straining during constipation. Some haemorrhoids require surgery to manage, which may involveplacing a band around the haemorrhoid, in order for it to lose blood supply; or surgical excision.[9]
Other
Anal abscesses usually result from infection of the normal glands of the anus, or sometimes because ofCrohn's disease.[9] They usually occur to the sides of the sphincters, and between the internal and external sphincters, either on the surface, or deeper. They may get bigger, enlarging in the direction of the rectum, and resulting in an abnormal connection called ananorectal fistula. They are usually managed with surgical drainage[9] and antibiotics.[10][11]
Additional
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Anal cancer, also called "anal carcinoma", andanal intraepithelial neoplasia.[12]
Itchiness, calledpruritus ani, can affect the anus area. It is most often due to long-term exposure of the anus to faeces, with reasons including diseases of the anus such as haemorrhoids, fistulas and fissures; poor hygiene or chronic diarrhoea; local infections such astapeworm andthrush; or skin conditions such aspsoriasis andcontact dermatitis. If there is a specific cause identified, the cause may be treated to relieve the itch. Otherwise, treatment includes keeping the area clean and dry, ceasing topical creams and ointments, and potentially bulk-forming laxatives to reduce the chance of faecal contamination.[9]
Damage or injury to the anal sphincter (patulous anus in more severe cases) as a result of damage during surgery, such as to theperineal region, or resulting fromanal sex; can lead toflatus and/orfecal incontinence, chronic constipation andmegacolon.[13]
The anus has a relatively high concentration ofnerve endings and can be anerogenous zone, which can make anal intercourse pleasurable if performed properly. The pudendal nerve that branches to supply the external anal sphincter also branches to thedorsal nerve of the clitoris and thedorsal nerve of the penis.[14]
In addition to nerve endings, pleasure from anal intercourse may be aided by the close proximity between the anus and theprostate for males, andvagina,clitorallegs and anal area for females. This is because of indirect stimulation of the prostate and vagina or clitoral legs.[14][15][16] For a male insertive partner, the tightness of the anus can be a source of pleasure via the tactile pressure on the penis.[17][18] Pleasure from the anus can also be achieved throughanal masturbation,anal fingering,[5]facesitting,anilingus, and other penetrative andnon-penetrative acts. Anal stretching orfisting is pleasurable for some, but it poses a more serious threat of damage due to the deliberate stretching of the anal and rectal tissues; its injuries include anal sphincter lacerations and rectal andsigmoid colon (rectosigmoid) perforation, which might result in death.[19] Lubricant andcondoms are widely regarded as a necessity while performing anal sex, as well as a slow and cautious penetration.[20]
Anal intercourse is sometimes referred to assodomy or buggery, and is consideredtaboo in a number of legal systems. It has been, and in somejurisdictions continues to be, a crime carrying severe punishment.[5]
To prevent diseases of the anus[citation needed] and to promote general hygiene, humans often clean the exterior of the anus after emptying the bowels. A rinse with water from abidet or a wipe withtoilet paper is often used for this purpose, though anal cleansing practices vary greatly between cultures.
Shaving, trimming,depilatory (hair removal), orBrazilian waxing can clear theperineum of hair.
Anal bleaching is a process in which the anus and perineum is lightened.Perineum sunning is a process in which the anus issun tanned by deliberate exposure to sunlight, resulting in a darkening of the area.[21]
A trueanal piercing is rare because it may interfere with the function of the anus and cause infections. Surface piercings of the perineum are easier to care for and much more common.
Some people have their anusestattooed.
The anus has many slang terms includingasshole,butthole (and their respective British equivalentsarsehole,bumhole),cornhole, andbunghole.
Many men find anal intercourse more exciting than penile-vaginal intercourse because the anal opening is usually smaller and tighter than the vagina. Probably the forbidden aspect of anal intercourse also makes it more exciting for some people.
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