Acid-base homeostasis · USMLE Step 1

What compensatory mechanism does the respiratory system provide in response to a primary metabolic acidosis?

  1. Decrease alveolar ventilation to retain CO₂
  2. Increase alveolar ventilation to blow off CO₂
  3. Activate renal bicarbonate reabsorption immediately
  4. Increase hepatic acidogenesis
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Correct answer: Increase alveolar ventilation to blow off CO₂

In metabolic acidosis (low HCO₃⁻ / high H⁺), the respiratory system increases ventilation to lower PaCO₂, reducing carbonic acid and helping partially normalize pH.

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