Question: It is not uncommon to see diarrhea when the enterohepatic bile salt circulation is disrupted.  For example, in a case of severe Crohn disease requiring a > 100 cm resection of terminal ileum, a patient starts to have profuse diarrhea.  The mechanism of this diarrhea is most similar to which other etiology of diarrhea?

A. cholera

B. lactase deficiency

C. dumping syndrome

D. lactulose administration

Answer: Diarrhea comes in two major categories, osmotic and secretory, although in practice there is frequent overlap.  When the enterohepatic circulation of bile salts is disrupted, as in the case of large resections of the terminal ileum, the bile salts cannot be absorbed and instead migrate distally into the colon.  The colonic mucosa is irritated by this detergent and a weeping, secretory process ensues. 

A secretory process is also seen in choleric diarrhea, when a constitutively activated chloride channel in the apical membrane leads to secretion of chloride into the intestinal lumen.  Cholestyramine is a binder of bile salts and prevents their interaction with the colonic wall; this occasionally relieves the diarrhea.  The other choices are all osmotic etiologies of diarrhea.

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