Lipids: pulmonary surfactant: 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 · Lipids: pulmonary surfactant

Sample item

A diabetic mother at 34 weeks has amniocentesis showing a lecithin to sphingomyelin ratio of 1.2. What is the correct interpretation?

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

The answer and the reasoning

C. Immature fetal lungs with a risk of respiratory distress syndrome

Surfactant is mainly dipalmitoylphosphatidylcholine (lecithin) made by type II pneumocytes. A lecithin to sphingomyelin ratio above 2 indicates lung maturity, and below 2 suggests risk of respiratory distress syndrome. Maternal diabetes delays surfactant synthesis because fetal hyperinsulinaemia antagonises the effect of cortisol.

Option by option

  • A. Fetal hypoxia from placental insufficiency

    Hypoxia is assessed by cardiotocography and Doppler, and does not change this ratio.

  • B. A neural tube defect in the fetus

    Neural tube defects are screened with alpha-fetoprotein, not with the lecithin to sphingomyelin ratio.

  • C. Immature fetal lungs with a risk of respiratory distress syndrome (correct)

    Correct. A ratio well below 2 predicts surfactant deficiency.

  • D. Mature fetal lungs, so delivery is safe without any lung-maturity measure

    A mature profile needs a ratio above 2, and this value is lower.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Immature fetal lungs with a risk of respiratory distress syndrome. Surfactant is mainly dipalmitoylphosphatidylcholine (lecithin) made by type II pneumocytes.

Why is "Fetal hypoxia from placental insufficiency" not the answer?

Hypoxia is assessed by cardiotocography and Doppler, and does not change this ratio.

Why is "A neural tube defect in the fetus" not the answer?

Neural tube defects are screened with alpha-fetoprotein, not with the lecithin to sphingomyelin ratio.

Why is "Mature fetal lungs, so delivery is safe without any lung-maturity mea…" not the answer?

A mature profile needs a ratio above 2, and this value is lower.

What concept does this question test?

It tests Lipids: pulmonary surfactant in Biochemistry. A lecithin to sphingomyelin ratio above 2 indicates lung maturity, and below 2 suggests risk of respiratory distress syndrome. Maternal diabetes delays surfactant synthesis because fetal hyperinsulinaemia antagonises the effect of cortisol.

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 Lipids: pulmonary surfactant?

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.