NBME Comprehensive Basic Science 3

Question 1

A 55-year-old man develops digitalis toxicity. Which electrolyte abnormality most potentiates this toxicity?

Accepted Answer

Hypokalemia

Answer

Hypokalemia potentiates digoxin toxicity because K+ and digoxin compete for the same binding site on the Na+/K+-ATPase.

Question 2

The Frank-Starling mechanism states that increased ventricular end-diastolic volume leads to which of the following?

Accepted Answer

Increased stroke volume

Answer

Greater sarcomere stretch from increased preload optimizes actin-myosin overlap, increasing the force of contraction and stroke volume.

Question 3

A patient with renal artery stenosis has elevated renin. Which of the following is the direct product of renin's enzymatic action?

Accepted Answer

Angiotensin I

Answer

Renin cleaves angiotensinogen to angiotensin I, which is then converted to angiotensin II by ACE in the lungs.

Question 4

A drug inhibits cyclooxygenase irreversibly. Which cell type is most functionally impaired because it cannot synthesize new enzyme?

Accepted Answer

Platelets

Answer

Platelets are anucleate and cannot synthesize new COX; aspirin's irreversible inhibition affects them for their entire 10-day lifespan.

Question 5

During a Valsalva maneuver, which phase is associated with a transient increase in venous return and cardiac output upon release?

Accepted Answer

Phase IV (post-release overshoot)

Answer

Phase IV shows reflex bradycardia and BP overshoot as thoracic venous blood surges back to the heart after intra-thoracic pressure normalizes.

NBME Practice Test