USMLE (United States Medical Licensing Examination) Practice Exam 11
Practice exam for USMLE (United States Medical Licensing Examination).
Question 1
MEDIUMA 58-year-old man with long-standing hypertension is started on a medication that decreases angiotensin II formation. Two weeks later, his serum creatinine increases from 1.0 mg/dL to 1.6 mg/dL. He feels well and has no edema. Which of the following changes in renal arteriolar tone most directly explains the rise in creatinine?
ACE inhibitors (and ARBs) reduce angiotensin II, which normally constricts the efferent arteriole to maintain glomerular capillary pressure and GFR. Loss of angiotensin II causes efferent arteriolar dilation, lowering intraglomerular pressure and decreasing GFR, which can raise creatinine. Afferent constriction would also lower GFR but is not the characteristic mechanism of ACE inhibition. Efferent constriction would increase intraglomerular pressure and tend to increase GFR.
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