Renal and acid–base: vulnerability of the outer medulla: 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: vulnerability of the outer medulla

Sample item

Which feature makes the thick ascending limb in the outer medulla especially vulnerable to acute tubular injury during hypotension?

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

The answer and the reasoning

A. High oxygen consumption by active transport with a low local PO2

Thick ascending limb cells perform heavy active NaCl transport that needs much oxygen, while countercurrent exchange in the vasa recta keeps the medullary PO2 low. A fall in perfusion therefore produces ischaemic injury here first.

Option by option

  • A. High oxygen consumption by active transport with a low local PO2 (correct)

    Correct. High oxygen demand meets a naturally low medullary PO2.

  • B. Complete dependence on glycolysis

    They are strongly dependent on oxidative metabolism and not on glycolysis.

  • C. Very high local blood flow

    Medullary blood flow is low compared with the cortex.

  • D. Absence of mitochondria in its cells

    These cells are rich in mitochondria, which supports their transport work.

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 A, High oxygen consumption by active transport with a low local PO2. Thick ascending limb cells perform heavy active NaCl transport that needs much oxygen, while countercurrent exchange in the vasa recta keeps the medullary PO2 low.

Why is "Complete dependence on glycolysis" not the answer?

They are strongly dependent on oxidative metabolism and not on glycolysis.

Why is "Very high local blood flow" not the answer?

Medullary blood flow is low compared with the cortex.

Why is "Absence of mitochondria in its cells" not the answer?

These cells are rich in mitochondria, which supports their transport work.

What concept does this question test?

It tests Renal and acid–base: vulnerability of the outer medulla in Physiology. A fall in perfusion therefore produces ischaemic injury here first.

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: vulnerability of the outer medulla?

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.