Human anus

Anus
The anus of a female (left, with prominent perineal raphe) and a male (right).
Identifiers
TA	A05.7.05.013
FMA	15711
Anatomical terminology []

The human anus (from Latin meaning "ring", "circle") is the external opening of the rectum. 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 vagina in females and behind the scrotum in males.

With anal sex, the anus can play a role in sexuality. Attitudes towards anal sex vary and it is illegal in some countries. The anus is often considered a taboo part of the body, and it is known by a large number of usually vulgar slang terms. The anus is also the site of potential infections and other conditions, including cancer. The traditional polite synonym for anus was , though this euphemism is rarely heard now that medical terms are widely acceptable.

The anus is the final component 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 defeaecation.

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. The pectinate line is also the division between the internal and external anus.