Renal Filtration and Electrolyte Balance · USMLE Step 1

In conditions of dietary potassium depletion, how does the kidney primarily reduce urinary K⁺ excretion?

  1. Increase electrogenic sodium reabsorption in distal nephron to drive K⁺ secretion
  2. Decrease K⁺ reabsorption in proximal tubule
  3. Decrease distal sodium delivery and reduce K⁺ channel abundance in principal cells
  4. Increase K⁺ filtration at glomerulus
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Correct answer: Decrease distal sodium delivery and reduce K⁺ channel abundance in principal cells

With low dietary potassium, distal sodium delivery is reduced and K⁺-secreting channels are downregulated in the distal nephron, decreasing K⁺ excretion to conserve potassium.

Difficulty: Medium Question 7 of 20

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