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Diarrhea is defined as a change in bowel movement pattern resulting
in an increase in stool volume and/or frequency, usually
with loose to watery stool consistency. Acute and chronic diarrhea are
defined based on duration of symptoms. Acute diarrhea lasts <14 days,
whereas chronic diarrhea persists for longer. In general, to be
considered diarrhea, three or more stools are passed per day. Patients
with chronic diarrhea may have periods of loose or frequent stools
with normal bowel movements in between episodes. Diarrhea can also
be defined based on stool volume; however, measuring this accurately
is often difficult. Normal stool volume is about 5–10 g
of stool/kg body weight/day for infants and about
100–200 g of stool/day in children and adults.
A 24-hour stool volume of >10 g/kg in infants and >200 g
in children and adults is considered diarrhea. Acute diarrhea is
common. It is most often secondary to viral infections. Other causes
of acute diarrhea include toxin-induced diarrhea and antibiotic-associated
diarrhea. Infectious diarrhea is most often found in children under
age 5 years with a rate of about one to three episodes per year. Causes
of chronic diarrhea are more diverse and range from functional disorders
such as Toddler’s diarrhea and irritable bowel syndrome
(IBS) to disorders that may impact overall health such as inflammatory
bowel disease or celiac disease.
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Diarrhea occurs due to a derangement in small bowel, colonic,
or pancreatic function. Besides the classification of acute and
chronic, diarrhea may be divided further by pathophysiologic mechanism
(Figure 4–1; Table 4–1).1 The
small bowel both secretes and absorbs water and electrolytes, as
well as absorbs nutrients. Imbalance between secretion and absorption
can lead to diarrhea. The primary function of the colon is to absorb
fluid and electrolytes as well as storage of its contents until
it can be expelled. The colon absorbs fluid and electrolytes. Disruption
of the colon’s function leads to frequent, loose, and occasionally
bloody stools. The motor function of the intestines regulates forward
propulsion of its contents. Abnormalities in this motility may also
lead to diarrhea.
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