Renal and acid–base: potassium loss in persistent vomiting: 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 loss in persistent vomiting

Sample item

A man with prolonged vomiting has metabolic alkalosis, volume depletion and a low serum potassium, with a high urinary potassium. Which mechanism contributes most to the renal potassium loss?

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

The answer and the reasoning

A. Aldosterone from volume depletion plus high distal flow with bicarbonate-rich urine

Volume depletion raises aldosterone, and bicarbonaturia from the alkalosis carries sodium to the distal nephron with an unreabsorbable anion. These conditions stimulate potassium secretion in the collecting duct. Gastric potassium loss is small compared with this renal loss.

Option by option

  • A. Aldosterone from volume depletion plus high distal flow with bicarbonate-rich urine (correct)

    Correct. Aldosterone and high distal flow with non-chloride anion promote potassium secretion.

  • B. Reduced distal sodium delivery

    Delivery of sodium to the distal nephron is increased, not reduced, by bicarbonaturia.

  • C. Direct loss of potassium in gastric fluid only

    Gastric juice contains little potassium, so this is a minor contribution.

  • D. Suppressed aldosterone secretion

    Aldosterone is raised, not suppressed, in volume depletion.

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, Aldosterone from volume depletion plus high distal flow with bicarbonate-rich urine. Volume depletion raises aldosterone, and bicarbonaturia from the alkalosis carries sodium to the distal nephron with an unreabsorbable anion.

Why is "Reduced distal sodium delivery" not the answer?

Delivery of sodium to the distal nephron is increased, not reduced, by bicarbonaturia.

Why is "Direct loss of potassium in gastric fluid only" not the answer?

Gastric juice contains little potassium, so this is a minor contribution.

Why is "Suppressed aldosterone secretion" not the answer?

Aldosterone is raised, not suppressed, in volume depletion.

What concept does this question test?

It tests Renal and acid–base: potassium loss in persistent vomiting in Physiology. These conditions stimulate potassium secretion in the collecting duct. Gastric potassium loss is small compared with this renal loss.

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 loss in persistent vomiting?

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.