TBR Passage XIV #94

[tipitinasjiggy]

Had a question about this one:

Which of the following conditions best describes a patient with a deficiency in PTH secretion

I. Hypocalcemia
II. Hypercalcemia
III. Hyperphosphatemia

My answer: A
TBR answer: C

I get the rationale they have in the book but feel like they are overlooking the impact that deficient PTH will have on dihydroxycholecalciferol. Ok so reduced PTH means decreased Ca uptake and reduced inhibition of PO4 reabsorption. So that is what they based their answer off.

But reduced PTH will lead to reduced activation of dihydroxycholecalciferol right? Which will reduce Ca and PO4 reabsorption...

In my mind Hypocalcemia is a definite answer, but Hyperphosphatemia isnt so clear. Theres a direct increase in PO4 reabsorption from PTH inhibition, but an indirect decrease in reabsorbtion from reduced dihydroxycholecalciferol.

Any error in my logic?

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[sazerac]

No error in your logic. This is more of a third year medical school topic, but when it comes to a parathyroid fight and the kidney is involved, the kidney always wins. Every time.

The fact that you caught this issue means you know more human physiology than is necessary for the MCAT. The real thing won't have a question like this that requires outside empiric knowledge.

Good catch!

 

[tipitinasjiggy]

Thanks so much for the response. Totally get your logic and that helps out a ton.

On a side note: NOLA med student? Sazerac was a giveaway! LA resident here, looking to come back to NOLA for med school.