Question 214

Question:

A 40-year-old woman receives an intravenous infusion of drug X that selectively constricts the efferent arterioles in her kidneys. Following the infusion, total cardiac output and renal afferent arteriolar tone are unchanged, but renal efferent arteriolar tone and total renal vascular resistance have both increased. Which of the following sets of changes most likely occurred following the infusion of drug X?

Correct Answer: E.  Increased GFR, Increased Filtration Fraction, Decreased Renal Blood Flow

Selective constriction of the efferent arterioles will cause the changes described in choice E. It will increase GFR by causing an increase in the glomerular capillary pressure causing an increase in the net pressure in the glomerulus. There will also be decreased renal blood flow as constriction of either the afferent or efferent arterioles will cause a decrease in perfusion to the kidneys. As the filtration fraction is the GFR devided by renal plasma flow, which is effectively renal blood flow, this number will increase as GFR has increased and renal blood flow has decreased.
The other choices give an incorrect combination of answers.