Introduction:

Inflammatory bowel disease (IBD) is a general term that covers two disorders:

• Ulcerative colitis (UC)
• Crohn's disease (CD)

Some evidence suggests that these two diseases are part of a biologic continuum. At this time, however, they are considered distinct disorders with somewhat different treatment options. The basic distinctions between UC and CD are location and severity. However, as many as 10% of patients with IBD have features and symptoms that match the criteria for both disorders, at least in the early stages. (This is called indeterminate colitis.)

Crohn's disease, also called regional enteritis, is a chronic inflammation of the intestines which is usually found in the terminal portion of the small intestine, the ileum. Ulcerative colitis is a similar inflammation of the colon, or large intestine. These and other IBDs (inflammatory bowel disease) have been linked with an increased risk of colorectal cancer.

Crohn's Disease. Crohn's disease is an inflammation that extends into the deeper layers of the intestinal wall. It is found most often in the area bridging the small and large intestines, specifically in the ileum and the cecum, sometimes referred to as the ileocecal region. Crohn's disease can occur less frequently in other parts of the gastrointestinal tract, including the anus, stomach, esophagus, and even the mouth. It may affect the entire colon or form a string of contiguous ulcers in one part of the colon. It may also develop as multiple scattered clusters of ulcers throughout the gastrointestinal tract, skipping healthy tissue in between.

Ulcerative Colitis. Ulcerative colitis is an inflammatory disease of the large intestine. Ulcers form in the inner lining, or mucosa, of the colon or rectum, often resulting in diarrhea, blood, and pus. The inflammation is usually most severe in the sigmoid and rectum and typically diminishes higher in the colon. The disease develops uniformly and consistently until, in some people, the colon becomes rigid and foreshortened. [For more information, see In-Depth Report #69: Ulcerative colitis.]

The Gastrointestinal Tract

The gastrointestinal tract (the digestive system) is a tube that extends from the mouth to the anus. It is a complex organ system that first carries food from the mouth down the esophagus to the stomach and then through the small and large intestine to be excreted out through the rectum and anus.

Esophagus. The esophagus, commonly called the food pipe, is a narrow muscular tube, about 9 1/2 inches long, that begins below the tongue and ends at the stomach.

Stomach. In the stomach, acids and stomach motion break food down into particles small enough so that nutrients can be absorbed by the small intestine.

Small Intestine. The small intestine, despite its name, is the longest part of the gastrointestinal tract and is about 20 feet long. Food that passes from the stomach into the small intestine first passes through three parts:

• First it enters the duodenum
• Then the jejunum, and
• Finally the ileum

Most of the digestive process occurs in the small intestine.

Large Intestine. Undigested material, such as plant fiber, is passed to the large intestine, mostly in liquid form. The large intestine is approximately 6 feet long and is the final portion of the digestive tract. It follows the small intestine and includes the cecum, the appendix, the colon, and the rectum, which extends to the anus.

Cecum and Appendix. The cecum and the appendix are located in the lower-right quadrant of the abdomen.

Colon. The colon absorbs excess water and salts into the blood. The remaining waste matter is converted to feces through bacterial action. The colon is divided into four major sections.

• The first section, the ascending colon, extends upward from the cecum on the right side of the abdomen.
• The second section, the transverse colon, crosses the upper abdomen to the left side.
• The third section extends downward on the left side of the abdomen toward the pelvis and is called the descending colon.
• The final section is the sigmoid colon.

Rectum and Anus. Feces are stored in the descending and sigmoid colon until they are passed through the rectum and anus. The rectum extends through the pelvis from the end of the sigmoid colon to the anus.