Overview of the anus and rectum

[Marquetta]

The anus is the opening at the end of the digestive tract where stool leaves the body.
The rectum is the section of the digestive tract above the anus where stool is held before it passes out of the body through the anus.
The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine. The rectal lining consists of glistening red tissue containing mucus glands—much like the rest of the intestinal lining. The lining of the rectum is relatively insensitive to pain, but the nerves from the anus and nearby external skin are very sensitive to pain.
The veins from the rectum and anus drain mostly into the portal vein, which leads to the liver, and then into the general circulation. Some of these veins drain directly into the pelvic veins and then into the general circulation. The lymph vessels of the rectum drain into lymph nodes in the lower abdomen. The lymph vessels of the anus drain into the lymph nodes in the groin.
A muscular ring (anal sphincter) keeps the anus closed. This sphincter is controlled subconsciously by the autonomic nervous system. However, part of the sphincter can be relaxed or tightened at will.
Disorders of the anus and rectum include

Anal cancer
Anal fissure
Anal itching
Anorectal abscess
Anorectal fistula
Colorectal cancer
Fecal incontinence
Foreign objects in the anus and rectum
Hemorrhoids
Levator syndrome
Pilonidal disease
Proctitis
Rectal prolapse