Human anus

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"Bumhole" redirects here. Not to be confused with Bunghole.
This article is about the anuses of humans. For the anuses of other animals, see Anus.

Human anus
Superficial inguinal lymph nodes
Identifiers
Latinanus
TA98A05.7.05.013
TA23022
FMA15711
Anatomical terminology]
Major parts of the
Gastrointestinal tract
Upper gastrointestinal tract
Lower gastrointestinal tract
See also

In humans, the anus (pl.: anuses or ani; from Latin ānus, "ring", "circle")[1][2] is the external opening of the rectum located inside the intergluteal cleft. Two sphincters control the exit of feces from the body during an act of defecation, which is the primary function of the anus. These are the internal anal sphincter and the external anal sphincter, which are circular muscles 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 the perineum, which is also located beneath the vulva or scrotum.

In part owing to its exposure to feces, a number of medical conditions may affect the anus, such as

hemorrhoids.[3] The anus is the site of potential infections and other conditions, including cancer (see anal cancer).[4]

With

anal warts
can be spread via anal sex.

Structure

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.[6]: 397  The anus is surrounded in its length by folds called anal valves, which converge at a line known as the pectinate line. This represents the point of transition between the hindgut and the ectoderm 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 the

inferior rectal nerves, which branch from the pudendal nerve.[7]

Microanatomy

The pseudostratified columnar epithelium of the gastrointestinal tract transitions to stratified squamous epithelium at the pectinate line. The stratified squamous epithelium gradually accumulates sebaceous and apocrine glands.[8]: 285 

Development

During

androgenic 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.

Function

Defecation

Main article: Defecation

Intra-rectal pressure builds as the rectum fills with feces, pushing the feces against the walls of the anal 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 and peristaltic 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 the levator ani muscles pull the anus up over the exiting feces.

Clinical significance

hemorrhoids. The pectinate line
, which separates the internal from the external anus, can be seen.

glyceryl trinitrate creams, and constipation is managed with laxatives and improving hydration.[9] Some fissures may require botulinum toxin injection; worst cases may require surgical intervention, such as "lateral internal anal sphincterotomy or advancement anoplasty"[clarification needed].[9]

make motions more soft and prevent straining during constipation. Some haemorrhoids require surgery to manage, which may involve placing a band around the haemorrhoid, in order for it to lose blood supply; or surgical excision.[9]

Other

Infections

anorectal fistula. They are usually managed with surgical drainage[9] and antibiotics.[10][11]

Additional

Cancer

anal intraepithelial neoplasia.[12]

Itching, incontinence and constipation

Itchiness, called

tapeworm and thrush; or skin conditions such as psoriasis and contact 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 (

flatus and/or fecal incontinence, chronic constipation and megacolon.[13]

Society and culture

Sexuality

Main article: Anal sex

The anus has a relatively high concentration of nerve endings and can be an erogenous zone, which can make anal intercourse pleasurable if performed properly. The pudendal nerve that branches to supply the external anal sphincter also branches to the dorsal nerve of the clitoris and the dorsal 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 the

condoms 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 as sodomy or buggery, and is considered taboo in a number of legal systems. It has been, and in some jurisdictions continues to be, a crime carrying severe punishment.[5]

Hygiene

Main article: Anal hygiene

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 a bidet or a wipe with toilet paper is often used for this purpose, though anal cleansing practices vary greatly between cultures.

Cosmetics

Shaving, trimming,

Brazilian waxing can clear the perineum
of hair.

Anal bleaching is a process in which the anus and perineum is lightened.

True anal piercing is rare because it may interfere with the function of the anus. Surface piercings of the perineum are easier to care for and much more common.

Additional images

  • Muscles of the male perineum
    Muscles of the male perineum
  • Muscles of the female perineum
    Muscles of the female perineum
  • The posterior aspect of the rectum and anus exposed by removing the lower part of the sacrum and the coccyx
    The posterior aspect of the rectum and anus exposed by removing the lower part of the sacrum and the coccyx

See also

Look up anus in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Human anus.

References

  1. ^ Martim de Albuquerque (1873). Notes and Queries. Original from the University of Michigan: Oxford University Press. p. 119.
  2. ^ O'Reilly, Edward; O'Donovan, John (1864). An Irish-English Dictionary. Original from Oxford University: J. Duffy. p. 7.
  3. PMID 19598294
    .
  4. ^ "Anal Cancer". The Lecturio Medical Concept Library. Retrieved 24 July 2021.
  5. ^ a b c d "Anal Sex, defined". Discovery.com. Archived from the original on June 13, 2002. Retrieved July 23, 2013.
  6. ^
    ISBN 978-0-8089-2306-0
    .
  7. ISBN 9781451119459
    .
  8. ^ Young, Barbara; Lowe, James S.; Stevens, Alan; Heath, John W. (2006). Wheater's functional histology: a text and colour atlas (5th ed.). Churchill Livingstone, Elsevier.
  9. ^
    ISBN 978-0-7020-7028-0
    .
  10. ^ "Anorectal Abscess". Johns Hopkins Medicine. Archived from the original on 10 August 2021. Retrieved 10 August 2021.
  11. ^ Ansorge, R; Robinson, J (15 September 2019). "Anal Abscess". WebMD. Retrieved 10 August 2021.
  12. ^ "Anal Cancer". The Lecturio Medical Concept Library. Retrieved 10 August 2021.
  13. ^ "Megacolon". The Lecturio Medical Concept Library. Retrieved 10 August 2021.
  14. ^
    ISBN 978-0-8018-9396-4
    . Retrieved January 20, 2014.
  15. ISBN 978-0-618-75571-4
    . Retrieved September 17, 2012.
  16. ISBN 978-1-61608-311-3
    . Retrieved November 6, 2011.
  17. ^ Dunkin, Mary Anne. "Anal Sex Safety: What to Know". WebMD. Retrieved August 19, 2013.
  18. ISBN 978-0-395-29724-7
    . Retrieved November 6, 2011. 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.
  19. ISBN 978-0275995089
    . Retrieved September 15, 2014.
  20. ISBN 978-0-495-60274-3
    . Retrieved 2010-12-19.
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