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Pathogenesis of acute diarrhea in children

Mark A Gilger, MD
Section Editor
William J Klish, MD
Deputy Editor
Alison G Hoppin, MD


Diarrhea is one of the most common causes of morbidity and mortality in children worldwide. Worldwide childhood death secondary to diarrhea declined from an estimated five million per year in 1980 to less than two million in 1999 [1]. The decline is generally attributed to global improvements in sanitation and the use of oral rehydration therapy.

The word diarrhea is derived from the Greek "diarrhoia", meaning to flow through. In clinical terms, diarrhea refers to either an increased stool frequency or a decreased stool consistency, typically a watery quality. Acute diarrhea is generally defined as lasting less than two weeks. Depending upon the etiology, the stool frequency can be dramatic. As an example, patients with cholera may have 20 or more episodes per day.

The evaluation and management of an infant or child with diarrhea requires an understanding of the pathophysiology of diarrhea and water absorption in the gastrointestinal tract. The physiology of fluid absorption and the pathogenesis of acute diarrhea will be discussed here. The approach to diagnosis and treatment are presented separately. Discussions on specific etiologies of acute diarrhea can be found in the corresponding topic reviews. (See "Approach to diarrhea in children in resource-rich countries" and "Treatment of hypovolemia (dehydration) in children".)


The intestine (both the small bowel and colon) is remarkably efficient in its ability to absorb water. The small bowel absorbs the vast majority of the body's fluid needs. Thus, diseases affecting the small bowel can result in significant diarrhea.

The small intestine is presented with approximately eight liters of fluid each day in healthy adults. This amount includes both ingested liquids and secretions contributed by salivary glands and the intestine. By the time the initial eight liters of fluid reaches the ileocecal valve, only about 600 mL remain, representing an efficiency of water absorption of 93 percent [2]. By the time the remaining 600 mL of fluid reaches the anus, only about 100 mL of fluid remains, generally as formed feces [2]. Combined, the efficiency of water absorption in the small and large intestine is approximately 99 percent under normal conditions.


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Literature review current through: May 2017. | This topic last updated: Mar 11, 2016.
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