Gastrointestinal: bile acid diarrhoea: 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 · Gastrointestinal: bile acid diarrhoea

Sample item

A man with Crohn's disease has had 40 cm of terminal ileum resected. He now has watery diarrhoea without marked steatorrhoea, which improves with cholestyramine. Which mechanism explains the diarrhoea?

AUnabsorbed bile acids inhibit colonic bacteria and cause constipationBLoss of vitamin B12 absorption inhibits water absorptionCUnabsorbed bile acids reach the colon and stimulate water and electrolyte secretionDExcess fat in the stool causes osmotic diarrhoea

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

The answer and the reasoning

C. Unabsorbed bile acids reach the colon and stimulate water and electrolyte secretion

The terminal ileum reabsorbs bile acids, and after a limited resection the liver can compensate by increasing synthesis, so fat absorption stays near normal. The bile acids that reach the colon stimulate colonic secretion and motility, causing watery diarrhoea, which binding resins such as cholestyramine reduce.

Option by option

A. Unabsorbed bile acids inhibit colonic bacteria and cause constipation
Bile acids in the colon cause diarrhoea rather than constipation.
B. Loss of vitamin B12 absorption inhibits water absorption
B12 malabsorption causes anaemia and neurological problems, not diarrhoea through water malabsorption.
C. Unabsorbed bile acids reach the colon and stimulate water and electrolyte secretion (correct)
Correct. Bile acids in the colon act as secretagogues and speed transit.
D. Excess fat in the stool causes osmotic diarrhoea
Steatorrhoea is not marked in a limited resection, and it would not respond to cholestyramine.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Unabsorbed bile acids reach the colon and stimulate water and electrolyte secretion. The terminal ileum reabsorbs bile acids, and after a limited resection the liver can compensate by increasing synthesis, so fat absorption stays near normal.

Why is "Unabsorbed bile acids inhibit colonic bacteria and cause constipation" not the answer?

Bile acids in the colon cause diarrhoea rather than constipation.

Why is "Loss of vitamin B12 absorption inhibits water absorption" not the answer?

B12 malabsorption causes anaemia and neurological problems, not diarrhoea through water malabsorption.

Why is "Excess fat in the stool causes osmotic diarrhoea" not the answer?

Steatorrhoea is not marked in a limited resection, and it would not respond to cholestyramine.

What concept does this question test?

It tests Gastrointestinal: bile acid diarrhoea in Physiology. The bile acids that reach the colon stimulate colonic secretion and motility, causing watery diarrhoea, which binding resins such as cholestyramine reduce.

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 Gastrointestinal: bile acid diarrhoea?

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.