Figure 48.14 Carbon Dioxide Is Transported as Bicarbonate Ions The left panel represents the circulation through the tissues of the body where carbonic anhydrase (CA) in capillary endothelial cells and in RBCs facilitates conversion of CO2 produced in the tissues to bicarbonate ions in the blood. The right panel shows the process reversing in the lungs as CO2 diffuses from blood to alveolar air and is exhaled.