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NBME 13 Answers

nbme13/Block 4/Question#35 (4.1 difficulty score)
A 55-year-old man with hepatic encephalopathy ...

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submitted by skip_lesions(10),

Colonic bacteria convert lactulose into lactic acid and acetic acid, which acidifies colonic contents. This leads to the conversion of ammonia (NH3), which is a weak base, into its nonabsorbable protonated form, ammonium (NH4+). Once protonated, the positive charge prevents ammonium from crossing cell membranes, keeping the molecule in the colon. As the levels of ammonia in circulation gradually declines, the symptoms of hepatic encephalopathy improve