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Retired NBME Step 2 CK Form 8 Answers

step2ck_form8/Block 3/Question#1 (reveal difficulty score)
A 52-year-old woman comes to the physician ...
Decreased lactase activity in the brush border ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: GI

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 +2  upvote downvote
submitted by โˆ—azibird(279)
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Was anyone else torn because you thought the colonic hydrogen travelled backwards up the entire gut to be exhaled via mouth fart? So that the small-bowel must have decreased pH?

Maybe just me...

Well apparently that's not how the test works. Or the human body. "The hydrogen produced by the bacteria is absorbed through the wall of the small or large intestine or both. The hydrogen-containing blood travels to the lungs where the hydrogen is released and exhaled in the breath where it can be measured." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3155069/

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 +1  upvote downvote
submitted by โˆ—step_prep(148)
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  • Middle-aged woman experiencing increased abdominal cramps and diarrhea associated with increased milk consumption, consistent with lactose intolerance
  • Key idea: Pathophysiology is that many people lose activity of the lactase enzyme on the brush border of their small bowel as they become adults, such that lactose can no longer be broken down into glucose and galactose and absorbed (remember that small bowel can only accept carbohydrate monomers)
  • Key idea: Lactose hydrogen breath test would be positive because the lactose would not be absorbed in the small bowel and would therefore travel into the large intestine, where there are many bacteria that will break down the lactose via anaerobic glycolysis, leading to release of hydrogen gas (and cause of bloating in patients)

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