The Haldane effect describes which property of CO₂ transport in blood?
- A Deoxygenated hemoglobin carries more CO₂ as carbamino-Hb and raises blood CO₂ content at the same PCO₂ compared to oxygenated Hb ✓
- B Increasing PCO₂ shifts the oxyhemoglobin dissociation curve to the right (Bohr effect)
- C CO₂ more soluble in plasma than O₂; total CO₂ transport is primarily as dissolved gas
- D Carbon monoxide binds hemoglobin with 240× higher affinity than oxygen
Explanation
The Haldane effect states that deoxygenated (reduced) hemoglobin is a better carbamino-CO₂ carrier and better buffer for H⁺ (from carbonic acid) than oxygenated Hb. This is because deoxy-Hb has more available amino groups (especially Val-1 of β-chain) for carbamino formation and higher pKa histidines for H⁺ buffering. At the same PCO₂, deoxygenated blood carries more CO₂. This effect facilitates CO₂ loading in tissues (where Hb becomes deoxygenated) and CO₂ unloading in the lung (where Hb becomes oxygenated), accounting for approximately 30% of total CO₂ transport.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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