Why We Exhale: Removing CO₂ and Regulating Lung Volume, Not Excess O₂

Primary Purpose

Exhalation eliminates carbon dioxide (CO₂), a metabolic waste product, and maintains gas balance and lung volume.

Gas Exchange Cycle

1. Inhale: O₂‑rich air enters alveoli.
2. O₂ diffuses into blood; CO₂ diffuses from blood into alveoli.
3. Exhale: CO₂‑rich air leaves lungs.

Not About Excess Oxygen

Blood O₂ is tightly regulated; exhalation does not primarily remove “extra” O₂.