Detailed Composition and Differences of Inspired and Expired Air

  1. Oxygen Diffusion Gradient

    • Respiring cells consume oxygen, lowering blood oxygen concentration.

    • Oxygen diffuses down its concentration gradient from alveoli into blood.

  2. Carbon Dioxide Excretion

    • Respiration produces carbon dioxide as waste, which enters blood.

    • Diffuses from higher concentration in blood into alveoli to be exhaled.

  3. Water Vapour Evaporation

    • Body heat evaporates water from the moist alveolar lining into expired air.

  4. Inert Role of Nitrogen

    • Nitrogen is chemically unreactive and unused by the body, remaining constant at 78%78\% in expired air.