Acid-base homeostasis · USMLE Step 1

According to acid–base physiology, if bicarbonate concentration increases or PaCO₂ decreases, what happens to blood pH (assuming other factors constant)?

  1. pH decreases
  2. pH increases
  3. pH remains unchanged
  4. pH becomes strongly acidic
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Correct answer: pH increases

An increase in bicarbonate or decrease in CO₂ shifts the bicarbonate buffer equilibrium toward less H⁺, raising pH (alkalemia).

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