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Part of HP-02 — Breathing & Exchange of Gases

Breathing and Gas Exchange — 5 Exam-Day Bullets

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  1. BCD = 70-23-7: CO2 travels as Bicarbonate (70%), Carbaminohaemoglobin (23%), Dissolved (7%). Never reverse — 70% is always HCO3–.

  2. RV ≠ FRC: RV (1100–1200 mL) = air after MAXIMUM FORCED expiration; FRC (2100–2300 mL) = ERV + RV = air after NORMAL expiration. VC excludes RV; TLC includes RV.

  3. Inspiration muscles = DEx (Diaphragm + External intercostals): Quiet expiration is PASSIVE (elastic recoil). Forced expiration = Internal intercostals + Abdominals.

  4. Right shift = lower O2 affinity = MORE O2 released (CADET: CO2↑, Acid↑, DPG↑, Exercise, Temp↑): Left shift = higher affinity = O2 retained (e.g., HbF, low temperature, alkalosis).

  5. 3-layered diffusion membrane (EBE): Alveolar Epithelium → Basement membrane → Capillary Endothelium. Gas exchange = simple diffusion; O2 gradient = 64 mmHg; CO2 gradient = 5 mmHg (CO2 is 20× more soluble).

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