In which form is the majority of CO2 carried in the blood?

The majority of carbon dioxide (CO2) is transported in the blood as bicarbonate (HCO3). This is a crucial part of the carbon dioxide transport system. When CO2 enters red blood cells, it interacts with water to form carbonic acid, which is a reversible reaction facilitated by the enzyme carbonic anhydrase. Carbonic acid then dissociates into bicarbonate and hydrogen ions.

This bicarbonate is then transported in the plasma to the lungs, where it can be converted back into CO2 and exhaled. This method of transport is efficient and is responsible for about 70% of CO2 transport in the blood. The bicarbonate buffer system also plays a vital role in maintaining the pH balance in the body.

While some CO2 is transported dissolved in plasma and some is bound to hemoglobin (forming carbaminohemoglobin), these forms account for a lesser amount of CO2 transport compared to bicarbonate. This highlights the importance of the bicarbonate system not just in transport, but also in regulating blood pH and facilitating gas exchange in the lungs.