Regarding carbon dioxide transport in blood, all of the following are true EXCEPT:

Explanation

## Carbon Dioxide Transport Pathways **Key Point:** Dissolved CO₂ in plasma accounts for only ~5-10% of total CO₂ transport, NOT 20-25%. ### Quantitative Distribution of CO₂ Transport | Transport Mechanism | Percentage | Details | |---------------------|-----------|----------| | Bicarbonate (HCO₃⁻) | ~70% | Formed via carbonic acid; transported in plasma | | Carbaminohemoglobin | ~20% | CO₂ bound directly to amino groups of Hb | | Dissolved CO₂ | ~5-10% | Dissolved in plasma; follows Henry's law | **High-Yield:** The 70-20-10 ratio is a classic NEET PG memory aid for CO₂ transport distribution. ### The Chloride Shift (Hamburger Phenomenon) ```mermaid flowchart LR A[CO₂ enters RBC] --> B[CO₂ + H₂O → H₂CO₃] B --> C[H₂CO₃ → H⁺ + HCO₃⁻] C --> D[HCO₃⁻ exits RBC] D --> E[Cl⁻ enters RBC] E --> F[Maintains electrical neutrality] style A fill:#e1f5ff style F fill:#c8e6c9 ``` **Key Point:** The chloride shift maintains electroneutrality as negatively charged bicarbonate ions leave the red blood cell. ### Carbaminohemoglobin Formation **Mnemonic:** **CARB** — CO₂ binds to the **CARB**oxyl terminus of hemoglobin globin chains (not the heme iron) - CO₂ + Hb → HbCO₂ (carbaminohemoglobin) - Accounts for ~20% of CO₂ transport - Deoxygenated hemoglobin has higher affinity for CO₂ (Haldane effect) **Clinical Pearl:** The Haldane effect is why venous blood can carry more CO₂ than arterial blood — deoxygenated hemoglobin in venous blood binds CO₂ more readily, facilitating CO₂ pickup from tissues. [cite:Guyton & Hall Ch 41]