UWorld Physiology 2

Question 1

During which phase of the cardiac cycle does left ventricular volume remain at its maximum?

Accepted Answer

Isovolumetric contraction

Answer

After the mitral valve closes and before the aortic valve opens, the ventricle contracts with volume fixed at end-diastolic volume.

Question 2

A patient stands up quickly from a supine position. Which immediate change occurs in the carotid sinus baroreflex?

Accepted Answer

Decreased baroreceptor firing and increased sympathetic outflow

Answer

Venous pooling lowers arterial pressure, reducing carotid sinus stretch and firing, which disinhibits sympathetic output.

Question 3

Oxygen consumption is 250 mL/min, arterial O2 content is 200 mL/L, and mixed venous O2 content is 150 mL/L. What is the cardiac output?

Accepted Answer

5 L/min

Answer

By the Fick principle, CO = 250 / (200 − 150) = 5 L/min.

Question 4

Which substance's clearance provides the most accurate measurement of glomerular filtration rate?

Accepted Answer

Inulin

Answer

Inulin is freely filtered and neither reabsorbed nor secreted, so its clearance equals GFR.

Question 5

Selective constriction of the efferent arteriole produces which combination of changes?

Accepted Answer

↑GFR, ↓RPF, ↑filtration fraction

Answer

Efferent constriction raises glomerular capillary pressure (↑GFR) while reducing plasma flow, so FF = GFR/RPF rises.

UWorld Practice Test