Confusion Regarding Questions from the Retired NBME Exams

[anondukie9]

One of the questions asks which will be decreased in a patient with severe diarrhea: Preload, Afterload, Both or Neither

The answer key suggests that the answer is both. Can someone explain why this is the case? Isn't this a case of hypovolemic shock? So after load should be high...

Also, another question asks which of the following will increase conversion of 25-OH hydroxycholecalciferol: Increase in PTH, decrease in blood calcium, increase in blood phosphate

The answer key says only increase in PTH and decrease in calcium are correct. However, a different question suggests that phosphate levels also regulate PTH. So why isn't an increase in phosphate also correct?

Any thoughts/suggestions are welcome. Thanks.

---

Members don't see this ad.

 

[studentdocftw]

No idea to both. I agree, with severe diarrhea presumably to the point of hypovolemia, preload is decreased as a result of dehydration, and SVR should be increased to compensate for lack of volume.

For the 2nd, PTH acts to increase calcium, decrease phosphate and increase vitD levels. Increase in PTH will result in increased 1 alpha hydroxylase activity, where in the kidney it acts to increase conversion of 25-OH. A decrease in blood Ca will result in increased PTH, resulting in increased conversion of 25-OH secondarily. Increase in blood phosphate also increases PTH activity, resulting in increased conversion of 25-OH, and increased phosphate wasting in the kidney.