What Is Diarrhea - Diarrhea: Digestive Disorders

Content provided by the Faculty of the Harvard Medical School

What is diarrhea?

Diarrhea is sometimes defined as having more than three bowel movements a day. But a more widely accepted definition of diarrhea is liquid or watery stools. When diarrhea occurs more than three-quarters of the time and lasts at least three months without an identifiable cause, the diarrhea is said to be functional.

Diarrhea is the body's response to something that upsets the intestines; it's the body's way of clearing out whatever is causing the upset. Sometimes you know exactly what caused the intestinal distress — for example, bacterial contamination in food. Other times, it remains a mystery.

In most cases, the problem will clear on its own, and you may not need to call a doctor. Diarrhea isn't usually serious, but it can lead to dehydration and weight loss. And while everybody experiences diarrhea sometimes, for a significant percentage of the population, the condition is persistent. Cases that don't clear in a few days — that is, chronic or functional cases — require a doctor's care.

How diarrhea works

Normal defecation depends on the small intestine, colon, rectum, and anal sphincter working normally. In diarrhea, something goes wrong.

The small intestine usually handles about eight liters of fluid from food and pushes about one liter to the colon. The colon absorbs most of this fluid and moves the compacted residue, which contains a few ounces of water, to the rectum. The rectum can store up to 200 grams of stool before defecation is triggered. However, any interference with this process can cause the colon to be overwhelmed by the fluid load, resulting in diarrhea. In fact, any disturbance in the colon that interferes with the packing, storage, or dehydrating of the stool can result in diarrhea.

Last updated:	August 21, 2007