Acid-base homeostasis · USMLE Step 1

What is the major non-volatile acid elimination pathway in kidneys during chronic acid loads (e.g., metabolic acidosis)?

  1. Excretion of CO₂ by lungs
  2. Ammonium (NH₄⁺) excretion
  3. Excretion of bicarbonate
  4. Sweat acidification
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Correct answer: Ammonium (NH₄⁺) excretion

Excretion of ammonium (NH₄⁺), generated from glutamine metabolism in renal cells, is quantitatively the most important mechanism for eliminating fixed acids in chronic acid load.

Difficulty: Medium Question 9 of 19

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