Blood in Respiration: O2/CO2 Transport, pH Regulation, Buffering, and Gas Exchange Facilitation

1. Oxygen Transport

98.5% bound to hemoglobin (Hb) as oxyhemoglobin; 1.5% dissolved in plasma. Cooperative binding (sigmoidal curve) enables loading in lungs (high pO₂) and unloading in tissues (low pO₂).

2. Carbon Dioxide Transport

• 70% as bicarbonate (HCO₃⁻) via carbonic anhydrase in RBCs.
• 23% as carbaminohemoglobin (Hb-CO₂).
• 7% dissolved in plasma.

3. pH Regulation (Acid-Base Balance)

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. Respiratory compensation: hyperventilation blows off CO₂ (raises pH); hypoventilation retains CO₂ (lowers pH). Renal compensation adjusts HCO₃⁻ reabsorption/excretion.

4. Buffering Systems

• Bicarbonate/carbonic acid (primary extracellular).
• Hemoglobin (intracellular; binds H⁺).
• Phosphate, proteins.

5. Gas Transport Integration

Haldane effect: deoxyHb binds more CO₂/H⁺; Bohr effect: H⁺/CO₂ reduce Hb-O₂ affinity. These reciprocal interactions optimize loading/unloading in lungs and tissues.