Renal and acid–base: glomerulotubular balance: 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 · Renal and acid–base: glomerulotubular balance

Sample item

In a healthy kidney, when the GFR rises moderately, the proximal tubule absorbs a larger absolute amount of sodium and water. What is this phenomenon called and what does it achieve?

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

The answer and the reasoning

D. Glomerulotubular balance, keeping fractional proximal reabsorption near two-thirds

Proximal reabsorption increases in proportion to the filtered load, so the reabsorbed fraction remains roughly constant at about two-thirds. This prevents large fluctuations in the delivery of solute to the distal nephron. It is partly explained by changes in peritubular oncotic pressure and luminal flow.

Option by option

  • A. Pressure natriuresis

    Pressure natriuresis refers to the rise in sodium excretion with arterial pressure.

  • B. Autoregulation of renal blood flow

    Autoregulation stabilises renal blood flow and GFR, not tubular reabsorption.

  • C. Tubuloglomerular feedback, lowering the GFR

    Tubuloglomerular feedback adjusts GFR in response to macula densa signals.

  • D. Glomerulotubular balance, keeping fractional proximal reabsorption near two-thirds (correct)

    Correct. Reabsorption follows the filtered load, so the fraction stays constant.

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 D, Glomerulotubular balance, keeping fractional proximal reabsorption near two-thirds. Proximal reabsorption increases in proportion to the filtered load, so the reabsorbed fraction remains roughly constant at about two-thirds.

Why is "Pressure natriuresis" not the answer?

Pressure natriuresis refers to the rise in sodium excretion with arterial pressure.

Why is "Autoregulation of renal blood flow" not the answer?

Autoregulation stabilises renal blood flow and GFR, not tubular reabsorption.

Why is "Tubuloglomerular feedback, lowering the GFR" not the answer?

Tubuloglomerular feedback adjusts GFR in response to macula densa signals.

What concept does this question test?

It tests Renal and acid–base: glomerulotubular balance in Physiology. This prevents large fluctuations in the delivery of solute to the distal nephron. It is partly explained by changes in peritubular oncotic pressure and luminal flow.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Renal and acid–base: glomerulotubular balance?

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.