Renal and acid–base: renal ammonium excretion: 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: renal ammonium excretion

Sample item

A patient with chronic metabolic acidosis from kidney disease excretes more acid over several days without a change in urinary pH. Which adaptation provides most of the increased acid excretion?

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

The answer and the reasoning

C. Increased ammonium production and excretion

Proximal tubular glutamine metabolism rises in chronic acidosis, producing ammonium that is trapped in the collecting duct lumen. This is the main adaptive route since titratable acid is limited by filtered buffer.

Option by option

  • A. Reduced glutamine uptake

    Glutamine uptake rises, not falls, in chronic acidosis.

  • B. Increased titratable acid as phosphate

    Titratable acid is limited by the amount of filtered phosphate.

  • C. Increased ammonium production and excretion (correct)

    Correct. Ammonium excretion is the major adaptive increase in acid excretion.

  • D. Increased bicarbonate reabsorption alone

    Bicarbonate reabsorption does not excrete acid.

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 C, Increased ammonium production and excretion. Proximal tubular glutamine metabolism rises in chronic acidosis, producing ammonium that is trapped in the collecting duct lumen.

Why is "Reduced glutamine uptake" not the answer?

Glutamine uptake rises, not falls, in chronic acidosis.

Why is "Increased titratable acid as phosphate" not the answer?

Titratable acid is limited by the amount of filtered phosphate.

Why is "Increased bicarbonate reabsorption alone" not the answer?

Bicarbonate reabsorption does not excrete acid.

What concept does this question test?

It tests Renal and acid–base: renal ammonium excretion in Physiology. This is the main adaptive route since titratable acid is limited by filtered buffer.

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: renal ammonium excretion?

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.