Endocrinology: FGF23: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Endocrinology: FGF23

Sample item

Which osteocyte-derived hormone lowers plasma phosphate by reducing phosphate reabsorption in the proximal tubule while also suppressing renal 1-alpha-hydroxylase?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Fibroblast growth factor 23

FGF23, acting with its co-receptor klotho, inhibits the sodium-phosphate cotransporter in the proximal tubule and suppresses 1-alpha-hydroxylase, lowering calcitriol. Its level rises in chronic kidney disease. PTH also reduces phosphate reabsorption but stimulates 1-alpha-hydroxylase.

Option by option

  • A. Calcitriol

    Calcitriol increases phosphate absorption from the gut and kidney.

  • B. Parathyroid hormone

    PTH causes phosphaturia but raises calcitriol synthesis.

  • C. Fibroblast growth factor 23 (correct)

    Correct. FGF23 lowers phosphate and calcitriol.

  • D. Calcitonin

    Calcitonin has little effect on phosphate handling in humans.

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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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Fibroblast growth factor 23. FGF23, acting with its co-receptor klotho, inhibits the sodium-phosphate cotransporter in the proximal tubule and suppresses 1-alpha-hydroxylase, lowering calcitriol.

Why is "Calcitriol" not the answer?

Calcitriol increases phosphate absorption from the gut and kidney.

Why is "Parathyroid hormone" not the answer?

PTH causes phosphaturia but raises calcitriol synthesis.

Why is "Calcitonin" not the answer?

Calcitonin has little effect on phosphate handling in humans.

What concept does this question test?

It tests Endocrinology: FGF23 in Physiology. Its level rises in chronic kidney disease. PTH also reduces phosphate reabsorption but stimulates 1-alpha-hydroxylase.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Endocrinology: FGF23?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.