Question

Most (~70%) of the CO2 that diffuses into systemic capillaries:

A. directly dissolves in the plasma
B. combines with water to form carbonic acid, which then dissociates to bicarbonate and hydrogen ions
C. binds to hemoglobin
D. forms carbonic anhydrase, which combines carbonic acid and water to solubilize the CO2.

Answer 1

Most carbon dioxide in the blood is transported as bicarbonate. Carbonic anhydrase in red blood cells converts CO₂ to carbonic acid, which dissociates into bicarbonate and hydrogen ions, supporting the bicarbonate buffer system.

Step-by-step explanation:

The question revolves around the transport of carbon dioxide (CO₂) in the blood, particularly within systemic capillaries. When CO₂ diffuses into these capillaries, approximately 70% gets converted into bicarbonate. The process involves CO₂ entering red blood cells, where the enzyme carbonic anhydrase facilitates its conversion to carbonic acid (H₂CO₃). This acid quickly dissociates into bicarbonate (HCO₃-) and hydrogen ions (H+).

The bicarbonate ions are then transported out of the red blood cells into the plasma, a process known as the chloride shift. Therefore, the majority of CO₂ is transported as part of the bicarbonate buffer system.