The purpose of the gastrointestinal (GI) tract is to extract fluid and essential nutrients from the food we eat and to eliminate wastes. All the way along the tract, food is propelled by involuntary rhythmic muscular contractions called peristalsis. From the mouth, ingested food proceeds down a straight tube called the esophagus into the stomach. It is here that the process of digestion begins, with stomach acid being secreted to break down food. Enzymes that also facilitate the breakdown of...
The purpose of the gastrointestinal (GI) tract is to extract fluid and essential nutrients from the food we eat and to eliminate wastes. All the way along the tract, food is propelled by involuntary rhythmic muscular contractions called peristalsis. From the mouth, ingested food proceeds down a straight tube called the esophagus into the stomach. It is here that the process of digestion begins, with stomach acid being secreted to break down food. Enzymes that also facilitate the breakdown of chemicals in food, permitting absorption into the bloodstream, are secreted here and in subsequent sections of the GI tract. From the stomach, food passes into the small intestine, a relatively thin, long (12 feet) tube with three distinct portions: duodenum, jejunum, and ileum. Enzymes from the pancreas and the gallbladder enter at the duodenum and have specific roles in the digestion of food. Generally several hours later, the remaining food passes from the ileum into the large intestine or colon. The appendix is a pouch of uncertain function close to the junction between the large and small intestines. Water and some remaining nutrients are extracted in the large intestine, before the remains are excreted through the rectum as stool.
Most of the time, the GI tract functions without problems, but there are a number of ways in which the system can go awry. Irritable bowel syndrome is a rather ill-defined syndrome said to affect 15% of people in Western countries. For unclear reasons, it appears to affect women more often than men. The essential elements of IBS are chronic abdominal pain associated with either constipation (constipation-predominant IBS) or diarrhea (diarrhea-predominant IBS); some patients alternate between constipation and diarrhea.
IBS itself is not a life-threatening condition, although it can be debilitating. The diagnosis of IBS should be based on a set of internationally recognized symptoms known as the Rome II Criteria (see box under alosetron (LOTRONEX)) and requires the exclusion of treatable causes of the patient’s symptoms, such as ulcerative colitis. This is especially important if the following signs of ulcerative colitis are present: onset after age 50, rectal bleeding, fever, weight loss, or anemia. There are no abnormal laboratory tests or changes in the cells of the GI tract on biopsy that can objectively establish the diagnosis of IBS. In fact, the diagnosis of IBS can only be made if all tests for other diseases that might explain the patient’s symptoms are negative. For young, otherwise healthy patients, extensive testing may not be necessary.
The FDA has approved drugs for both diarrhea-predominant and constipation-predominant IBS. The former, alosetron (LOTRONEX), had to be removed from the market after it caused serious constipation and a condition of decreased blood flow to the intestine called ischemic colitis. The latter, tegaserod (ZELNORM), has also been associated with ischemic colitis and severe, disabling diarrhea, and it is barely effective.
Instead, we recommend that you manage IBS through a combination of dietary and drug treatments targeted at your particular symptoms. There is also a report of a successful multidisciplinary approach, including psychological counseling, to this disease.