GI physiology: colonic function: 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 · GI physiology: colonic function

Sample item

A patient on prolonged broad-spectrum antibiotics develops watery diarrhoea. Which colonic function loss helps to explain this?

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

The answer and the reasoning

D. Reduced bacterial fermentation to short-chain fatty acids that fuel colonocytes and drive sodium absorption

Colonic bacteria ferment unabsorbed carbohydrate and fibre to short-chain fatty acids, mainly acetate, propionate and butyrate. Butyrate is the main fuel of colonocytes, and these acids also promote sodium and water absorption. Antibiotic disruption of the flora reduces them and leaves unabsorbed carbohydrate osmotically active, and may allow Clostridioides difficile overgrowth.

Option by option

  • A. Failure of bile acid synthesis in the liver

    Bile acid synthesis is hepatic and is not directly altered by antibiotics.

  • B. Reduced pancreatic bicarbonate secretion

    Pancreatic bicarbonate is unaffected by colonic flora.

  • C. Reduced mucus secretion by gastric surface cells

    Gastric mucus is unrelated to colonic bacterial changes.

  • D. Reduced bacterial fermentation to short-chain fatty acids that fuel colonocytes and drive sodium absorption (correct)

    Loss of short-chain fatty acids impairs colonocyte nutrition and fluid absorption.

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, Reduced bacterial fermentation to short-chain fatty acids that fuel colonocytes and drive sodium absorption. Colonic bacteria ferment unabsorbed carbohydrate and fibre to short-chain fatty acids, mainly acetate, propionate and butyrate.

Why is "Failure of bile acid synthesis in the liver" not the answer?

Bile acid synthesis is hepatic and is not directly altered by antibiotics.

Why is "Reduced pancreatic bicarbonate secretion" not the answer?

Pancreatic bicarbonate is unaffected by colonic flora.

Why is "Reduced mucus secretion by gastric surface cells" not the answer?

Gastric mucus is unrelated to colonic bacterial changes.

What concept does this question test?

It tests GI physiology: colonic function in Physiology. Butyrate is the main fuel of colonocytes, and these acids also promote sodium and water absorption. Antibiotic disruption of the flora reduces them and leaves unabsorbed carbohydrate osmotically active, and may allow Clostridioides difficile overgrowth.

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 GI physiology: colonic function?

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.