Lipid metabolism: bile acid diarrhoea after ileal resection: practice question

A Biochemistry 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

Biochemistry · Lipid metabolism: bile acid diarrhoea after ileal resection

Sample item

After resection of 60 cm of terminal ileum for Crohn disease, a man has watery diarrhoea but no steatorrhoea. The diarrhoea improves with cholestyramine. What explains the diarrhoea?

ALoss of the pancreatic lipase that digests triglyceridesBUnabsorbed bile acids reach the colon and stimulate water and electrolyte secretionCOvergrowth of bacteria that deconjugate vitamin B12DReduced uptake of lactose due to lost brush border lactase

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

The answer and the reasoning

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

The terminal ileum reabsorbs bile acids by an active transporter. After limited resection the liver can compensate for the loss, so fat absorption stays adequate, but excess bile acids in the colon stimulate secretion and cause watery diarrhoea. Bile acid sequestrants bind them and relieve it. Larger resections deplete the bile acid pool and cause steatorrhoea.

Option by option

A. Loss of the pancreatic lipase that digests triglycerides
Pancreatic lipase is secreted upstream and is unaffected by ileal resection.
B. Unabsorbed bile acids reach the colon and stimulate water and electrolyte secretion (correct)
Correct. Bile acids entering the colon stimulate secretion, and a sequestrant binds them.
C. Overgrowth of bacteria that deconjugate vitamin B12
Bacterial overgrowth can occur after resection but would not explain a response to a bile acid sequestrant.
D. Reduced uptake of lactose due to lost brush border lactase
Lactase is a jejunal brush border enzyme, so it is not lost by terminal ileal resection and 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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Unabsorbed bile acids reach the colon and stimulate water and electrolyte secretion. The terminal ileum reabsorbs bile acids by an active transporter.

Why is "Loss of the pancreatic lipase that digests triglycerides" not the answer?

Pancreatic lipase is secreted upstream and is unaffected by ileal resection.

Why is "Overgrowth of bacteria that deconjugate vitamin B12" not the answer?

Bacterial overgrowth can occur after resection but would not explain a response to a bile acid sequestrant.

Why is "Reduced uptake of lactose due to lost brush border lactase" not the answer?

Lactase is a jejunal brush border enzyme, so it is not lost by terminal ileal resection and would not respond to cholestyramine.

What concept does this question test?

It tests Lipid metabolism: bile acid diarrhoea after ileal resection in Biochemistry. After limited resection the liver can compensate for the loss, so fat absorption stays adequate, but excess bile acids in the colon stimulate secretion and cause watery diarrhoea. Bile acid sequestrants bind them and relieve it. Larger resections deplete the bile acid pool and cause steatorrhoea.

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 Lipid metabolism: bile acid diarrhoea after ileal resection?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.