In what form is CO2 transported in the blood?

Carbon dioxide (CO2) is primarily transported in the blood in three main forms, with the majority being carried as bicarbonate ions in the plasma. When CO2 is produced during cellular metabolism, it diffuses into red blood cells where it reacts with water to form carbonic acid, catalyzed by the enzyme carbonic anhydrase. This carbonic acid quickly dissociates into bicarbonate and hydrogen ions.

The bicarbonate ions then enter the plasma, which is the liquid component of blood that carries various substances, including electrolytes, nutrients, and waste products. A significant proportion of CO2—about 70%—is transported this way in the plasma.

While red blood cells, white blood cells, and platelets play essential roles in different functions within the circulatory system, they are not the primary carriers of CO2. Red blood cells are mainly responsible for transporting oxygen, white blood cells are crucial for immune defense, and platelets are involved in blood clotting. Therefore, the primary form of CO2 transport in the blood being in plasma as bicarbonate ions highlights the critical balance of gases necessary for maintaining the acid-base equilibrium in the body.