Last updated: 11/24/2009

The large bowel, also called the large intestine, is a part of the digestive system. It runs from the small bowel (small intestine) to the rectum, which receives waste material from the small bowel. Its major function is to store waste and to absorb...

water from waste material. It consists of the following sections, any of which may become diseased:

• Colon. The colon averages some 60 in (150 cm) in length. It is divided into four segments: the ascending colon, transverse colon, descending colon, and sigmoid colon. There are two bends (flexures) in the colon. The hepatic flexure is where the ascending colon joins the transverse colon. The splenic flexure is where the transverse colon merges into the descending colon.
• Cecum. This is the first portion of the large bowel that is joined to the small bowel. The appendix lies at the lowest portion of the cecum.
• Ascending colon. This segment is about 8 in (20 cm) in length, and it extends upwards from the cecum to the hepatic flexure near the liver.
• Transverse colon. This segment is usually more than 18 in (46 cm) in length and extends across the upper abdomen to the splenic flexure.
• Descending colon. This segment is usually less than 12 in (30 cm) long and extends from the splenic flexure downwards to the start of the pelvis.
• Sigmoid colon. An S-shaped segment that measures about 18 in (46 cm); it extends from the descending colon to the rectum.

The wall of the colon is composed of four layers:

• Mucosa. This single layer of cell lining is flat and regenerates itself every three to eight days. Small glands lie beneath the surface.
• Submucosa. The area between the mucosa and circular muscle layer that is separated from the mucosa by a thin layer of muscle, the muscularis mucosa.
• Muscularis propria. The inner circular and outer longitudinal muscle layers.
• Serosa. The outer, single-cell, thick covering of the bowel. It is similar to the peritoneum, the layer of cells that lines the abdomen.

The large intestine is also responsible for bacterial production and absorption of vitamins. Resection of a portion of the large intestine (or of the entire organ) may become necessary when it becomes diseased. The exact reasons for large bowel resection in any given patient may be complex and are always carefully evaluated by the treating physician or team. The procedure is usually performed to treat the following disorders or diseases of the large intestine:

• Cancer. Colon cancer is the second most common type of cancer diagnosed in the United States. Colon and rectum cancers, which are usually referred to as colorectal cancer, grow on the lining of the large intestine. Bowel resection may be indicated to remove the cancer.
• Diverticulitis. This condition is characterized by the inflammation of a diverticulum, especially of diverticula occurring in the colon, which may undergo perforation with abscess formation. The condition may be relieved by resecting the affected bowel section.
• Intestinal obstruction. This condition involves a partial or complete blockage of the bowel that results in the failure of the intestinal contents to pass through. It is usually treated by decompressing the intestine with suction, using a nasogastric tube inserted into the stomach or intestine. In cases where decompression does not relieve the symptoms, or if tissue death is suspected, bowel resection may be considered.
• Ulcerative colitis. This condition is characterized by chronic inflammation of the large intestine and rectum resulting in bloody diarrhea. Surgery may be indicated when medical therapy does not improve the condition. Removal of the colon is curative and also removes the risk of colon cancer. About 25–40% of ulcerative colitis patients must eventually have their colons removed because of massive bleeding, severe illness, rupture of the colon, or risk of cancer.
• Traumatic injuries. Accidents may result in bowel injuries that require resection.
• Pre-cancerous polyps. A colorectal polyp is a growth that projects from the lining of the colon. Polyps of the colon are usually benign and produce no symptoms, but they may cause rectal bleeding and develop into malignancies over time. When polyps have a high chance of becoming cancerous, bowel resection may be indicated.
• Familial adenomatous polyposis (FAP). This is a hereditary condition caused by a faulty gene. Most people discover that they have it at a young age. People with FAP grow many polyps in the bowel. These are mostly benign, but because there are so many, it is really only a question of time before one becomes cancerous. Since people with FAP have a very high risk of developing bowel cancer, bowel resection is thus often indicated.
• Hirschsprung's disease (HD). This condition usually occurs in children. It causes constipation, meaning that bowel movements are difficult. Some children with HD cannot have bowel movements at all; the stool creates a blockage in the intestine. If HD is not treated, stool can fill up the large intestine and cause serious problems such as infection, bursting of the colon, and even death.