i always get confused with this

[twesting2173]

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[acab]

I'm not sure about this one, but here's how I'd approach it:

Initially, not even looking at answers choices, vit D seems to be deficient (loose bulky stools, demineralization), so serum Ca is decreased, PTH will increase because body senses low serum Ca. As PTH increases, serum phosphate decreases (increased excretion), and I assume alkaline phosphatase increases because of bone destruction.

Choice A.

 

[xjacob]

Yeah, this stuff is always confusing to me as well. One hormone/electrolyte change leads to another, and the key is knowing at what equilibrium the sequence stops.
My method (not necessarily right), is just projecting the primary changes by the defect, trying to ignore any 2nd or 3rd line consquences (if possible). So with low vitD, you have low Ca (no absorption in the gut), and low P (no (re)absorption in the kidney and gut). PTH will rise (both low Ca and low vitD cause this).
Now the fact that PTH will try to bring up Ca (a SECONDARY effect) is true, but it is not going to be able to compensate (let alone overcompensate). Thus Ca will be low. PTH will also cause P wasting, and this just adds up to the low P caused by lack of vitD (so no ambiguity there).
And yes, a high bone turnover usu. implies high alk phosph.
So I agree with acab.