Renal and acid–base: potassium shift in mineral acidosis: 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: potassium shift in mineral acidosis

Sample item

Why does hyperkalaemia occur more readily in a metabolic acidosis due to hydrochloric acid loading than in lactic acidosis?

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

The answer and the reasoning

A. Chloride cannot enter cells with H+, so cells buffer H+ by exchange for K+

In mineral acidosis the anion remains in the extracellular fluid, so intracellular buffering of H+ requires cation exchange, and K+ moves out. Organic anions such as lactate enter cells together with H+, so there is little transcellular K+ shift. Insulin and beta-agonists move potassium into cells.

Option by option

  • A. Chloride cannot enter cells with H+, so cells buffer H+ by exchange for K+ (correct)

    Correct. The impermeant chloride anion forces H+ entry to be matched by K+ exit.

  • B. Lactic acid is fully buffered by the extracellular fluid

    Lactic acid is not completely buffered extracellularly, and this does not explain the difference.

  • C. Lactate anion drives K+ out of cells more strongly

    Organic anions enter with H+, so they lead to less K+ shift.

  • D. Hydrochloric acid stimulates insulin release

    Insulin would shift K+ into cells and lower the potassium.

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, Chloride cannot enter cells with H+, so cells buffer H+ by exchange for K+. In mineral acidosis the anion remains in the extracellular fluid, so intracellular buffering of H+ requires cation exchange, and K+ moves out.

Why is "Lactic acid is fully buffered by the extracellular fluid" not the answer?

Lactic acid is not completely buffered extracellularly, and this does not explain the difference.

Why is "Lactate anion drives K+ out of cells more strongly" not the answer?

Organic anions enter with H+, so they lead to less K+ shift.

Why is "Hydrochloric acid stimulates insulin release" not the answer?

Insulin would shift K+ into cells and lower the potassium.

What concept does this question test?

It tests Renal and acid–base: potassium shift in mineral acidosis in Physiology. Organic anions such as lactate enter cells together with H+, so there is little transcellular K+ shift. Insulin and beta-agonists move potassium into cells.

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 Renal and acid–base: potassium shift in mineral acidosis?

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.