Symposium on diarrhea. 1. Definition and mechanisms of diarrhea.

Diarrhea, an increase in frequency of evacuation and in water content of the stool, is the result of three categories of mechanism--solute malabsorption, secretion of fluid and motility disturbance. Before diarrhea is considered an abnormal condition, any alteration in stool frequency and content must be related to an individual person's normal bowel habit and to norms for the population, but more than three bowel movements or the passage of liquid stools exceeding 300 g daily should, in general, be considered abnormal. A useful way of understanding the mechanism of diarrhea is to become familiar with the normal functions of the bowel in regard to water and electrolyte absorption and motility, and then to relate these functions to solute malabsorption, fluid secretion and motility disturbance.