Renal Filtration and Electrolyte Balance · USMLE Step 1

Under conditions of volume depletion, activation of the renin–angiotensin–aldosterone system (RAAS) will have which effect on the nephron?

  1. Decrease sodium reabsorption in the proximal tubule
  2. Increase excretion of both sodium and water
  3. Reabsorb more sodium and water; excrete potassium
  4. Promote water excretion independent of sodium
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Correct answer: Reabsorb more sodium and water; excrete potassium

RAAS activation leads to aldosterone release, which increases sodium (and water) reabsorption and enhances potassium excretion — restoring fluid volume at the cost of increased K⁺ loss.

Difficulty: Medium Question 17 of 20

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