The anus is that part of the intestinal tract that passes through the muscular canal of the pelvis and anal sphincters. It is the final orifice through which stool passes out of the body. In adults, the anus is 4 to 5 centimeters long. The lower half of the anal canal has sensitive nerve endings.
The anus is an opening in the lower part of the digestive tract. When stool fills the rectum, the sphincter muscle relaxes, letting stool pass through the anus and out of the body. The external anal sphincter closes off the anus when stool has passed.
Sometimes anal cancer causes no symptoms at all. But bleeding is often the first sign of the disease. The bleeding is usually minor. At first, most people assume the bleeding is caused by hemorrhoids painful, swollen veins in the anus and rectum that may bleed. They are a benign and fairly common cause of rectal bleeding.