Irritable Bowel Syndrome (cont.)

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What are symptoms of irritable bowel syndrome (IBS)?

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The primary purpose of the gastrointestinal tract is to digest (break down) and absorb (take into the blood stream) food. In order to fulfill this purpose, food must be ground, mixed, and transported through the intestines, where it is digested and absorbed. In addition, undigested and unabsorbed portions of the food must be eliminated from the body.

In functional diseases of the gastrointestinal tract, the grinding, mixing, digestion, and absorption functions are disturbed to only a minor degree. These functions are essentially maintained, perhaps because of a built-in over-capacity of the gastrointestinal tract to perform these functions. The most commonly affected function in these diseases is transportation. In the stomach and small intestine, the symptoms of slowed transportation are nausea, vomiting, abdominal bloating (the sensation of abdominal fullness), and abdominal distention (enlargement). The symptom of rapid transportation usually is diarrhea. The interpretation of symptoms, however, may be more complicated than this. For example, let's say that a person has abnormally rapid emptying of the stomach. The sensing of this rapid emptying by the intestinal sensory nerves normally brings about a motor nerve response to slow down the emptying of the stomach and transportation through the small intestine. Thus, rapid emptying of the stomach may give rise to symptoms of slowed transportation.

In the colon, abnormally slow or rapid transportation results in constipation or diarrhea, respectively. In addition, there may be increased amounts of mucus coating the stool or a sense of incomplete evacuation after a bowel movement.

As discussed previously, normal sensations may be abnormally processed and perceived. Such an abnormality could result in abdominal bloating and pain. Abnormally processed sensations from the gastrointestinal organs also may lead to motor responses that cause symptoms of slow or rapid transportation.

Slow transportation of food through the small intestine may be complicated, for example, by bacterial overgrowth. In bacterial overgrowth, gas-producing bacteria that are normally restricted to the colon move up into the small intestine. There, they are exposed to greater amounts of undigested food than in the colon, which they turn into gas. This formation of gas can aggravate bloating and/or abdominal distention and result in increased amounts of flatus (passing gas, or flatulence) and diarrhea.

The gastrointestinal tract has only a few ways of responding to diseases. Therefore, the symptoms often are similar regardless of whether the diseases are functional or non-functional. Thus, the symptoms of both functional and non-functional gastrointestinal diseases are nausea, vomiting, bloating, abdominal distention, diarrhea, constipation, and pain. For this reason, when functional disease is being considered as a cause of symptoms, it is important that the presence of non-functional diseases be excluded (ruled out). In fact, the exclusion of non-functional diseases is more important in evaluating patients who are suspected of having functional disease because the tests for diagnosing functional disease are complex, not readily available, and often not very reliable. In contrast, the tests for diagnosing non-functional diseases are widely available and sensitive (able to diagnose most cases). IBS is often referred to by medical personnel as a "diagnosis of exclusion."

Medically Reviewed by a Doctor on 10/15/2014

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