Renal Filtration and Electrolyte Balance · USMLE Step 1

Which of the following correctly explains how the kidney conserves potassium when dietary potassium is low?

  1. By increasing distal sodium delivery to enhance potassium secretion
  2. By reducing sodium reabsorption throughout the nephron
  3. By reducing distal flow and downregulating K⁺ secretory channels
  4. By increasing glomerular filtration of potassium
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Correct answer: By reducing distal flow and downregulating K⁺ secretory channels

In potassium depletion, the kidney reduces distal tubular flow and downregulates luminal K⁺ channels in the distal nephron, thereby reducing K⁺ secretion and conserving body potassium.

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