THE ANUS
The anus is the opening where the gastrointestinal tract ends and exits the body. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine). The anorectal line separates the anus from the rectum.
Tough tissue called fascia surrounds the anus and attaches it to nearby structures.
Circular muscles called the external sphincter ani form the wall of the anus and hold it closed. Glands release fluid into the anus to keep its surface moist.
A plate-like band of muscles, called the levator ani muscles, surround the anus and form the floor of the pelvis. A network of veins lines the skin of the anus.
The abundance of nerve endings in the anal region and rectum can make anal sex pleasurable for men or women. The internal and external sphincter muscles control the opening and closing of the anus; these muscles, which are sensitive membranes made up of many nerve endings, facilitate pleasure or pain during anal sex.
ANAL SEX
Anal sex or anal intercourse is generally the insertion and thrusting of the erect penis into a person's anus, or anus and rectum, for sexual pleasure. Other forms of anal sex include fingering, the use of sex toys for anal penetration, oral sex performed on the anus (anilingus), and pegging.
While anal sex is commonly associated with male homosexuality, not all gay males engage in anal sex and it is not uncommon in heterosexual relationships. Types of anal sex can also be a part of lesbian sexual practices. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect stimulation of the clitoris or an area of the vagina (sometimes called the G-spot) in women, and other sensory nerves. However, people may also find anal sex painful, sometimes extremely so, which may be primarily due to psychological factors in some cases.
Anal sex is considered a high-risk sexual practice because of the vulnerability of the anus and rectum. The anal and rectal tissues are delicate and do not provide lubrication like the vagina does, so they can easily tear and permit disease transmission, especially if a personal lubricant is not used.
MALE TO FEMALE
The anal sphincters are usually tighter than the pelvic muscles of the vagina, which can enhance the sexual pleasure for the inserting male during male-to-female anal intercourse because of the pressure applied to the penis. Men may also enjoy the penetrative role during anal sex because of its association with dominance, because it is made more alluring by a female partner or society in general insisting that it is forbidden, or because it presents an additional option for penetration.
While some women find being a receptive partner during anal intercourse painful or uncomfortable, or only engage in the act to please a male sexual partner, other women find the activity pleasurable or prefer it to vaginal intercourse.
MALE TO MALE
Among men who have anal sex with other men, the insertive partner may be referred to as the top and the one being penetrated may be referred to as the bottom. Those who enjoy either role may be referred to as versatile.
Gay men who prefer anal sex may view it as their version of intercourse and a natural expression of intimacy that is capable of providing pleasure. Some men who have sex with men, however, believe that being a receptive partner during anal sex questions their masculinity.
Men who have sex with men may also prefer to engage in frot or other forms of mutual masturbation because they find it more pleasurable or more affectionate, to preserve technical virginity, or as safe sex alternatives to anal sex.
FEMALE TO MALE
Women may sexually stimulate a man's anus by fingering the exterior or interior areas of the anus; they may also stimulate the perineum (which, for males, is between the base of the scrotum and the anus), massage the prostate or engage in anilingus. Sex toys, such as a dildo, may also be used. The practice of a woman penetrating a man's anus with a strap-on dildo for sexual activity is called pegging.
FEMALE TO FEMALE
With regard to lesbian sexual practices, anal sex includes fingering, use of a dildo or other sex toys, or anilingus. Some lesbians do not like anal sex, and anilingus is less often practiced among female same-sex couples.