Lipid metabolism: cholestasis and fat malabsorption: 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.

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Biochemistry · Lipid metabolism: cholestasis and fat malabsorption

Sample item

A 55-year-old man with a carcinoma obstructing the common bile duct has pale, greasy stools. Which defect in lipid digestion explains the steatorrhoea?

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

The answer and the reasoning

D. Failure of bile salts to reach the gut and form micelles

Bile salts emulsify dietary fat and form mixed micelles that carry fatty acids and monoacylglycerol to the enterocyte. With biliary obstruction they cannot reach the gut, so fat and fat-soluble vitamins are malabsorbed. Pancreatic lipase and colipase remain normal.

Option by option

  • A. Failure of apoB-48 synthesis in enterocytes

    ApoB-48 failure is a rare inherited defect of chylomicron assembly and does not result from bile duct obstruction.

  • B. Absence of pancreatic colipase

    Colipase deficiency impairs lipase function but is not caused by an obstructing bile duct tumour.

  • C. Loss of brush-border lactase

    Lactase deficiency leads to osmotic diarrhoea from lactose, not fatty stools.

  • D. Failure of bile salts to reach the gut and form micelles (correct)

    Correct. Without bile salts in the gut, micelles cannot form and fat is malabsorbed.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Failure of bile salts to reach the gut and form micelles. Bile salts emulsify dietary fat and form mixed micelles that carry fatty acids and monoacylglycerol to the enterocyte.

Why is "Failure of apoB-48 synthesis in enterocytes" not the answer?

ApoB-48 failure is a rare inherited defect of chylomicron assembly and does not result from bile duct obstruction.

Why is "Absence of pancreatic colipase" not the answer?

Colipase deficiency impairs lipase function but is not caused by an obstructing bile duct tumour.

Why is "Loss of brush-border lactase" not the answer?

Lactase deficiency leads to osmotic diarrhoea from lactose, not fatty stools.

What concept does this question test?

It tests Lipid metabolism: cholestasis and fat malabsorption in Biochemistry. With biliary obstruction they cannot reach the gut, so fat and fat-soluble vitamins are malabsorbed. Pancreatic lipase and colipase remain normal.

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 Lipid metabolism: cholestasis and fat malabsorption?

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.