Renal Filtration and Electrolyte Balance · USMLE Step 1

Which of the following statements about potassium handling by the kidney is correct under normal dietary potassium intake?

  1. All filtered potassium is reabsorbed, so none appears in urine
  2. Freely filtered, mostly reabsorbed proximally, then fine-tuned distally
  3. Potassium is mostly secreted in the proximal tubule
  4. Potassium is neither filtered nor reabsorbed by the nephron
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Correct answer: Freely filtered, mostly reabsorbed proximally, then fine-tuned distally

Potassium is freely filtered at the glomerulus; a large portion is reabsorbed (e.g., proximal tubule), and the distal nephron/collecting duct adjust K⁺ excretion to match dietary intake and maintain balance.

Difficulty: Medium Question 13 of 20

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