Renal and acid–base: osmotic diuresis: 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: osmotic diuresis

Sample item

A man with uncontrolled diabetes mellitus has polyuria and glycosuria, and his plasma glucose is 450 mg/dL. Which mechanism accounts for the polyuria?

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

The answer and the reasoning

D. Unreabsorbed glucose holds water in the tubular lumen, limiting water reabsorption

When the filtered load of glucose exceeds the proximal transport maximum, the excess stays in the tubular fluid and exerts an osmotic effect that reduces water reabsorption along the nephron. The result is an osmotic diuresis with loss of water and electrolytes.

Option by option

  • A. Excess ADH secretion lowers water reabsorption

    ADH would increase, not decrease, water reabsorption.

  • B. Increased aquaporin-2 expression in the collecting duct

    Greater aquaporin-2 expression would increase water reabsorption and concentrate the urine.

  • C. Aldosterone excess promotes sodium and water excretion

    Aldosterone promotes sodium retention, not loss.

  • D. Unreabsorbed glucose holds water in the tubular lumen, limiting water reabsorption (correct)

    Correct. Non-reabsorbed solute retains water in the tubule.

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 D, Unreabsorbed glucose holds water in the tubular lumen, limiting water reabsorption. When the filtered load of glucose exceeds the proximal transport maximum, the excess stays in the tubular fluid and exerts an osmotic effect that reduces water reabsorption along the nephron.

Why is "Excess ADH secretion lowers water reabsorption" not the answer?

ADH would increase, not decrease, water reabsorption.

Why is "Increased aquaporin-2 expression in the collecting duct" not the answer?

Greater aquaporin-2 expression would increase water reabsorption and concentrate the urine.

Why is "Aldosterone excess promotes sodium and water excretion" not the answer?

Aldosterone promotes sodium retention, not loss.

What concept does this question test?

It tests Renal and acid–base: osmotic diuresis in Physiology. The result is an osmotic diuresis with loss of water and electrolytes.

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: osmotic diuresis?

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.