Carbon Dioxide Transport in the Blood

Carbon dioxide (CO₂) transport in the blood is critical to human physiology. On average, our body cells produce around 200 mL of CO₂ per minute, precisely the quantity expelled by the lungs. This process involves the transportation of CO₂ from the tissue cells to the lungs in three primary forms.

Forms of CO₂ Transport

1. Dissolved in plasma: A small percentage (7-10%) of CO₂ is transported and dissolved directly in the plasma.

2. Carbaminohemoglobin: Just over 20% of CO₂ is chemically bound to hemoglobin, forming

carbaminohemoglobin. In this process, CO₂ binds directly to the amino acids of globin, not the heme part of hemoglobin. pCO₂ levels significantly influence the formation of carbaminohemoglobin. High pCO₂ levels in tissue capillaries promote carbaminohemoglobin formation, while low pCO₂ levels in pulmonary capillaries facilitate the separation of CO₂ from globin, allowing it to enter the alveoli via diffusion.

3. Bicarbonate ions (HCO₃^–): Approximately 70% of CO₂ is transported as bicarbonate ions in the blood plasma. This process begins when CO₂ diffuses into systemic capillaries and enters red blood cells, where it reacts with water under the influence of the enzyme carbonic anhydrase to form carbonic acid. This acid then dissociates into H⁺ and HCO₃^–. In the lungs, the process reverses, and CO₂ is released to be exhaled.

The Haldane effect

The amount of CO₂ transported in the blood is profoundly affected by the degree of blood oxygenation, known as the Haldane effect. This effect states that lower pO₂ and hemoglobin oxygen saturation allow the blood to carry more CO₂ due to an increased affinity of hemoglobin for CO₂ in these conditions.

Summary

The transport of CO2 in the blood is a complex but efficient process, primarily involving the formation of carbaminohemoglobin and bicarbonate ions. This intricate system ensures the body maintains a stable balance of CO2 production and expulsion, a testament to the body's remarkable regulatory mechanisms, which are crucial for optimal physiological functioning.