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The sigmoid colon is the end portion of the large intestine, nearest the rectum. This portion of the intestine is in the form of an s-shaped loop, and is usually approximately 16 inches (40.64 cm) in length. It is able to expand and contract dependent upon the amount of fecal material being stored until it is ready to be evacuated from the body.
The colon is also known as the large intestine or bowel. The colon is comprised of the ascending, transverse, descending, and sigmoid colons, as well as the rectum and anus. The purposes of the colon are to eliminate toxins and wastes from the body, to absorb and transfer nutrients into the bloodstream, and to absorb fluids.
The colon is one long tube that begins at the end of the small intestine. The entire colon measures approximately 5 feet (1.5 m) long, much shorter than the typical 16 feet (4.8 m) of small intestine. It is composed of lymphatic and connective tissues, blood vessels, and muscles. The muscle tissue is responsible for the movement, or peristalsis, necessary to propel waste through the colon.
Most of the water is absorbed from feces as it moves through the ascending colon. The waste then moves on to the transverse colon, beginning at the hepatic flexure. This is the portion of the colon in which the waste is formed into stool. At the splenic flexure, the transverse colon becomes the descending colon, where stools become more solid.
The s-shaped sigmoid colon begins at the end of the descending colon. Stools continue through the sigmoid colon, and may be stored in this area until they are moved into the rectum. The rectum is a short section of bowel that leads to the anus, where stool is expelled.
Since one of the most common causes of cancer death in the United States is colon cancer, many health professionals recommend a sigmoidoscopy for men and women over the age of 50. This procedure evaluates the sigmoid colon for polyps or other lesions. During the procedure, the doctor can visualize the inner lining of this part of the colon, remove polyps, and take tissue samples for biopsy.
As the sigmoid colon must increase pressure to move stool into the rectum, occasional bulging sacs called diverticuli may form. These small sacs, if infected, cause a condition known as diverticulitis, which may be accompanied by abdominal pain and fever. Diagnosis is generally made with a sigmoidoscopy. Treatment will likely include anti-spasmodic drugs and antibiotics.