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Physiology · Endocrine physiology
Sample itemWhat is the main immediate effect of parathyroid hormone on serum calcium homeostasis?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
A. Increase serum calcium concentration
Parathyroid hormone raises serum calcium by acting on bone and kidney and by increasing activation of vitamin D, while it promotes renal phosphate excretion rather than complete phosphate retention.
Option by option
A. Increase serum calcium concentration (correct)
Correct: PTH acts to raise circulating calcium.
B. Lower serum calcium by blocking bone turnover
Blocking bone turnover and lowering calcium is not PTH's main action.
C. Increase insulin sensitivity only
Insulin sensitivity is not the principal calcium-regulating action of PTH.
D. Reduce renal phosphate excretion completely
PTH increases, not eliminates, renal phosphate excretion.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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