Cardiovascular system: coronary circulation: 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 · Cardiovascular system: coronary circulation

Sample item

During exercise, myocardial oxygen demand rises, yet the heart cannot meet it by extracting more oxygen from each unit of blood. Why not?

AMyocardial cells store large amounts of oxygenBOxygen extraction in the coronary circulation is already about 70 percent at restCHaemoglobin affinity for oxygen is too low in the coronary circulationDCoronary veins do not drain into the coronary sinus

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

The answer and the reasoning

B. Oxygen extraction in the coronary circulation is already about 70 percent at rest

The myocardium extracts around 70 percent of delivered oxygen even at rest, so coronary sinus blood is highly desaturated. Extra oxygen must come from increased coronary blood flow, driven by metabolic vasodilators such as adenosine.

Option by option

A. Myocardial cells store large amounts of oxygen
The myocardium stores very little oxygen, mostly bound to myoglobin.
B. Oxygen extraction in the coronary circulation is already about 70 percent at rest (correct)
Correct. Near-maximal resting extraction leaves flow as the only way to raise supply.
C. Haemoglobin affinity for oxygen is too low in the coronary circulation
Haemoglobin affinity is the same as elsewhere and is not the limiting factor.
D. Coronary veins do not drain into the coronary sinus
Most coronary venous blood does drain into the coronary sinus.

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 B, Oxygen extraction in the coronary circulation is already about 70 percent at rest. The myocardium extracts around 70 percent of delivered oxygen even at rest, so coronary sinus blood is highly desaturated.

Why is "Myocardial cells store large amounts of oxygen" not the answer?

The myocardium stores very little oxygen, mostly bound to myoglobin.

Why is "Haemoglobin affinity for oxygen is too low in the coronary circulation" not the answer?

Haemoglobin affinity is the same as elsewhere and is not the limiting factor.

Why is "Coronary veins do not drain into the coronary sinus" not the answer?

Most coronary venous blood does drain into the coronary sinus.

What concept does this question test?

It tests Cardiovascular system: coronary circulation in Physiology. Extra oxygen must come from increased coronary blood flow, driven by metabolic vasodilators such as adenosine.

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 Cardiovascular system: coronary circulation?

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.