Renal Pathophysiology Practice Test

A 70-year-old man with long-standing diabetes and hypertension presents with fatigue and ankle swelling. Meds: amlodipine, insulin, atorvastatin. Exam: BP 168/92 mmHg, periorbital edema, 2+ pitting edema. Labs: BUN 46 mg/dL, creatinine 2.6 mg/dL, K 5.2 mmol/L, HCO3− 19 mmol/L; eGFR 26 mL/min/1.73 m². Urine albumin-to-creatinine ratio: 980 mg/g. Renal ultrasound: bilaterally small echogenic kidneys. What is the underlying pathophysiological process causing these symptoms?

A 52-year-old man presents with 24 hours of oliguria after starting gentamicin for sepsis. History: type 2 diabetes, HTN; meds: lisinopril, metformin. Exam: euvolemic, mild flank tenderness. Urinalysis: muddy brown granular casts, no RBC casts; FeNa 3.2%. Labs: BUN 48 mg/dL, creatinine 4.1 mg/dL (baseline 1.0), K 5.8 mmol/L, HCO3− 18 mmol/L, phosphate 5.6 mg/dL. Renal ultrasound: normal-sized kidneys, no hydronephrosis. Which of the following mechanisms best explains this patient's renal findings?