Renal and acid-base: metabolic alkalosis: 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.

Try it

Physiology · Renal and acid-base: metabolic alkalosis

Sample item

A 5-week-old infant with projectile vomiting has plasma Cl 82 mmol/L, K 2.9 mmol/L and bicarbonate 38 mmol/L, yet the urine is acidic. What explains the paradoxical aciduria?

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

The answer and the reasoning

D. Volume depletion and hypokalaemia drive aldosterone-mediated sodium reabsorption with hydrogen secretion in the distal nephron

Vomiting loses gastric hydrochloric acid, causing hypochloraemic alkalosis and volume contraction. Raised aldosterone promotes sodium reabsorption in exchange for potassium and hydrogen ions, and potassium depletion also favours hydrogen secretion, so the urine is acid despite systemic alkalosis. Saline with potassium corrects the problem.

Option by option

  • A. Excess hydrogen ion loss from the stomach is excreted again in the urine

    Hydrogen ion is lost from the stomach and is not returned to the urine.

  • B. Lactic acid from hypoperfusion overrides the alkalosis in urine

    Lactate is not the cause of the aciduria in pyloric stenosis.

  • C. Distal renal tubular acidosis impairs bicarbonate generation

    Distal RTA causes acidosis, not alkalosis, with an alkaline urine.

  • D. Volume depletion and hypokalaemia drive aldosterone-mediated sodium reabsorption with hydrogen secretion in the distal nephron (correct)

    Correct. Sodium conservation takes priority over acid-base balance, so hydrogen is secreted.

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.

More Physiology questions

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Volume depletion and hypokalaemia drive aldosterone-mediated sodium reabsorption with hydrogen secretion in the distal nephron. Vomiting loses gastric hydrochloric acid, causing hypochloraemic alkalosis and volume contraction.

Why is "Excess hydrogen ion loss from the stomach is excreted again in the ur…" not the answer?

Hydrogen ion is lost from the stomach and is not returned to the urine.

Why is "Lactic acid from hypoperfusion overrides the alkalosis in urine" not the answer?

Lactate is not the cause of the aciduria in pyloric stenosis.

Why is "Distal renal tubular acidosis impairs bicarbonate generation" not the answer?

Distal RTA causes acidosis, not alkalosis, with an alkaline urine.

What concept does this question test?

It tests Renal and acid-base: metabolic alkalosis in Physiology. Raised aldosterone promotes sodium reabsorption in exchange for potassium and hydrogen ions, and potassium depletion also favours hydrogen secretion, so the urine is acid despite systemic alkalosis. Saline with potassium corrects the problem.

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: metabolic alkalosis?

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.