Potassium Handling

A 52-year-old man with chronic kidney disease (eGFR 28 mL/min/1.73 m²) presents with fatigue and palpitations. His wife reports he has been taking an ACE inhibitor for hypertension for the past 6 months. Laboratory investigations reveal: Na⁺ 138 mEq/L, K⁺ 6.8 mEq/L, Cl⁻ 104 mEq/L, HCO₃⁻ 22 mEq/L, creatinine 2.1 mg/dL. ECG shows peaked T waves and prolonged PR interval. Which of the following mechanisms best explains the hyperkalemia in this patient?

In the collecting duct, which cell type is primarily responsible for potassium secretion?

A 68-year-old woman with type 2 diabetes mellitus presents to the emergency department with severe muscle weakness and an irregular heartbeat. Her medications include metformin, insulin, and a thiazide diuretic for hypertension. Laboratory values are: K⁺ 2.9 mEq/L, Na⁺ 142 mEq/L, Cl⁻ 108 mEq/L, HCO₃⁻ 28 mEq/L, glucose 280 mg/dL, pH 7.48. ECG shows U waves and flattened T waves. Which renal mechanism is primarily responsible for the potassium wasting in this patient?

Which segment of the nephron is responsible for the majority of potassium reabsorption?