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. Young, Barbara; Lowe, James S.; Stevens, Alan; Heath, John W. (2006). Wheater's functional histology: a text and colour atlas (5thed.). Churchill Livingstone, Elsevier. During puberty, as testosterone triggers 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. 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. Some sexually transmitted infections including HIV/AIDS and anal warts can be spread via anal sex.

Rosenthal, Martha (2012). Human Sexuality: From Cells to Society. Cengage Learning. pp.133–135. ISBN 978-0-618-75571-4 . Retrieved September 17, 2012. O'Reilly, Edward; O'Donovan, John (1864). An Irish-English Dictionary. Original from Oxford University: J. Duffy. p.7.Moore, Keith L.; Dalley, Arthur F.; Agur, A. M. R. (2013-02-13). Clinically Oriented Anatomy. Lippincott Williams & Wilkins. ISBN 9781451119459. The anus is the final part of the gastrointestinal tract, and directly continues from the rectum. The anus passes through the pelvic floor. The anus is surrounded by muscles. 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 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 Miletich, John J.; Tia Laura Lindstrom (2010). An Introduction to the Work of a Medical Examiner: From Death Scene to Autopsy Suite. ABC-CLIO. p.29. ISBN 978-0275995089 . Retrieved September 15, 2014. A GREAT FAMILY GAME FOR ADULTS AND KIDS: Looking for fun new family card games or family-friendly animal quizzes? This new and amusing card game is loved by adults and teenagers and makes a hilarious party game to play with friends and family! Makes a great travel game that can also be played at home on the sofa, or at a table. It’s a perfect addition to holiday games!

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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 and separated from the genitals by the perineum. 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 relaxes as required by normal physiological functioning. The inner sphincter is involuntary and the outer is voluntary. It is located behind the perineum which is located behind the vulva or scrotum. a b Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell (2005). Gray's anatomy for students. illustrations by Richard; Richardson, Paul. Philadelphia: Elsevier/Churchill Livingstone. ISBN 978-0-8089-2306-0. Anorectal Abscess". Johns Hopkins Medicine. Archived from the original on 10 August 2021 . Retrieved 10 August 2021.

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. Damage or injury to the anal sphincter ( patulous anus in more severe cases) as a result of damage during surgery, such as to the perineal region, or resulting from anal sex; can lead to flatus and/or fecal incontinence, chronic constipation and megacolon. [13] Martim de Albuquerque (1873). Notes and Queries. Original from the University of Michigan: Oxford University Press. p.119. a b Komisaruk, Barry R.; Whipple, Beverly; Nasserzadeh, Sara; Beyer-Flores, Carlos (2009). The Orgasm Answer Guide. JHU Press. pp.108–109. ISBN 978-0-8018-9396-4 . Retrieved January 20, 2014.

Anal cancer, also called "anal carcinoma", and anal intraepithelial neoplasia. [12] Itching, incontinence and constipation