What is the pathophysiology of diarrhea in gastroenteritis?

Updated: Feb 10, 2017
  • Author: Arthur Diskin, MD; Chief Editor: Steven C Dronen, MD, FAAEM  more...
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Infectious agents are the usual cause of acute gastroenteritis. These agents cause diarrhea by several mechanisms, including adherence, mucosal invasion, enterotoxin production, and/or cytotoxin production.

These mechanisms result in increased fluid secretion and/or decreased absorption. This produces an increased luminal fluid content that cannot be adequately reabsorbed, leading to dehydration and the loss of electrolytes and nutrients.

Diarrheal illnesses may be classified as follows:

  • Osmotic, due to an increase in the osmotic load presented to the intestinal lumen, either through excessive intake or diminished absorption

  • Inflammatory (or mucosal), when the mucosal lining of the intestine is inflamed

  • Secretory, when increased secretory activity occurs

  • Motile, caused by intestinal motility disorders

The small intestine is the prime absorptive surface of the gastrointestinal tract. The colon then absorbs additional fluid, transforming a relatively liquid fecal stream in the cecum to well-formed solid stool in the rectosigmoid.

Disorders of the small intestine result in increased amounts of diarrheal fluid with a concomitantly greater loss of electrolytes and nutrients.

Microorganisms may produce toxins that facilitate infection. Enterotoxins, generated by some bacteria (ie, enterotoxigenic Escherichia coli, Vibrio cholera) act directly on secretory mechanisms and produce a typical, copious watery (rice water) diarrhea. No mucosal invasion occurs. The small intestines are primarily affected, and an elevation of the adenosine monophosphate (AMP) levels is the common pathogenic mechanism.

Cytotoxin production by other bacteria (ie, Shigella dysenteriae, Vibrio parahaemolyticus, Clostridium difficile, enterohemorrhagic E coli) results in mucosal cell destruction that leads to bloody stools with inflammatory cells. A resulting decreased absorptive ability occurs.

Enterocyte invasion is the preferred method by which microbes such as Shigella and Campylobacter organisms and enteroinvasive E coli cause destruction and inflammatory diarrhea. Similarly, Salmonella and Yersinia species also invade cells but do not cause cell death. Hence, dysentery does not usually occur. However, these bacteria invade the bloodstream across the lamina propria and can cause enteric fevers such as typhoid.

Diarrheal illness occurs when microbial virulence overwhelms the normal host defenses. A large inoculum may overwhelm the host capacity to mount an effective defense. Normally, more than 100,000 E coli are required to cause disease, while only 10 Entamoeba,Giardia cysts, or norovirus particles may suffice to do the same. Some organisms (eg, V cholera, enterotoxigenic E coli) produce proteins that aid their adherence to the intestinal wall, thereby displacing the normal flora and colonizing the intestinal lumen.

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