The anus is located at the end of the digestive tract; it is the passage way that excretes stool.
In anatomy, the anus (from Latin ?nus "ring, anus") is the external opening of the rectum. Closure is controlled by sphincter muscles. Feces are expelled from the body through the anus during the act of defecation, which is the primary function of the anus. Most animals — from simple worms to elephants and humans — have a tubular gut, with a mouth at one end and an anus at the other.
The human anus is situated between the buttocks, posterior to the perineum. It has two anal sphincters, one internal, the other external. These hold the anus closed until time to defecate. One sphincter consists of smooth muscle and its action is involuntary; the other consists of striated muscle and its action is voluntary. In many animals, the anus is surrounded by anal sacs.
Role in defecation
When the rectum is full, the increase in intrarectal pressure forces the walls of the anal canal apart allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincters of the anus allow the feces to be passed by muscles pulling the anus up over the exiting feces.
To prevent diseases of the anus and to promote general hygiene, humans often clean the anus after emptying the bowels. A wash with a bidet or a wiping with toilet paper are often used to clear the anus of fecal matter.
During puberty, as testosterone triggers hair growth on the body, pubic hair begins to appear around the anus. Although intially sparse, it fills out by the end of puberty, if not earlier.
Hygiene is important for good anal health and anal sex. Washing with a mild soap and water will keep the anus clean. Harsh soaps or wiping vigorously with toilet paper can irritate the skin around the anus, making it itchy or sore.
Care should be taken not to strip the anus of natural oils that keep the skin around the opening supple and elastic.
Kegel exercises can improve the tone of the outer sphincter muscle.
There are many health conditions that can affect the anus. Generally conditions of the digestive tract, such as Crohn's disease, Ulcerative colitis, Inflammatory bowel disorder, or any other conditions that impact the regularity of the stool. Those who suffer chronic diarrhea or constipation, often have issues in the anus, such as fistulas, skin tags, or hemorrhoids.