Rectum

About the Rectum

The rectum is the final straight section of the large intestine, lying in the pelvis in front of the sacrum and continuing from the sigmoid colon to the anal canal. Despite its name, from the Latin for straight, it has several curves. Its wall can stretch to store feces, and stretch receptors in the wall signal the urge to defecate. Continence is maintained by the internal anal sphincter, an involuntary smooth muscle, the voluntary external anal sphincter, and the puborectalis muscle, which forms a sling around the junction of the rectum and anal canal. Defecation involves coordinated relaxation of these muscles and contraction of the abdominal wall. The rectum is one of the most common sites of colorectal cancer, which is why it is examined during colonoscopy and sigmoidoscopy screening. Other conditions include hemorrhoids, which arise from vascular cushions in the anal canal, rectal prolapse, and proctitis, inflammation of the rectal lining that can occur in ulcerative colitis.