How is Carbon Dioxide transported?
In addition to its role in O2 transport, hemoglobin helps transport CO2 and assists in buffering the blood - that is, preventing harmful changes in pH.
Only about 7% of the CO2 released by respiring cells is transported in solution in blood plasma.
Another 23% binds to the amino ends of hemoglobin polypeptide chains, and about 70% is transported in the blood in the form of bicarbonate ions (HCO3-)
Carbon dioxide from respiring cells diffuses into the blood plasma and then into enthrocytes.
There the CO2 reacts with water (assisted by the enzyme carbonic anhydrase) and foms H2CO3, which dissociates into H+ and HCO3-.
Most of the H+ binds to hemoglobin and other proteins, minimizing the change in blood pH.
The HCO3 diffuses into the plasma.
When blood flows through the lungs, the relative partial presures of CO2 favor the diffusion of CO2 out of the blood
As CO2 diffuses into alveoli, the amount of CO2 in the blood decreases.
This decrease shifts the chemical equilibrium in favour of the conversion of HCO3- to CO2 enabling further net diffusion of CO2 into alveoli