Renal System MCAT Practice Question
A 68-year-old man with a 10-year history of type 2 diabetes mellitus presents with progressive dyspnea and lower extremity edema. Laboratory studies show serum creatinine 4.2 mg/dL (baseline 0.9), potassium 5.8 mEq/L, and bicarbonate 18 mEq/L. Plasma renin activity is markedly elevated at 12 ng/mL/hr (normal: 1-4), but aldosterone level is only 8 ng/dL (normal: 4-30 in upright position). Urinalysis reveals 3+ proteinuria. Blood pressure is 162/94 mmHg. Which of the following best explains the paradoxically low aldosterone level despite elevated renin activity in this patient?
Answer choices
- AAldosterone synthase inhibition by accumulated uremic toxins in advanced renal failure
- BReduced angiotensinogen synthesis due to hepatic dysfunction from diabetic cirrhosis
- CImpaired conversion of angiotensin I to angiotensin II by ACE inactivation
- DAdrenal infiltration by diabetic amyloidosis causing zona glomerulosa atrophy
- EVolume expansion-mediated suppression of aldosterone that overwhelms the renin signalCorrect answer
- FLoss of juxtaglomerular cell responsiveness to hypotension and hyperkalemia
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