Carbon dioxide (CO_2) diffuses into blood from tissue site and...

Blood is the medium of transport of $\mathrm{O}_2$ and $\mathrm{CO}_2$. Nearly 20-25 \% of $\mathrm{CO}_2$ is transported by RBCs as carbaminohaemoglobin whereas $70 \%$ of it is carried as bicarbonate through plasma. About $7 \% of \mathrm{CO}_2$ is carried in dissolved state through plasma. The largest fraction of $\mathrm{CO}_2$ is converted to bicarbonate ions \left(\mathrm{HCO}_3^{-}\right)$and transported in plasma. When$\mathrm{CO}_2$diffuses into the RBCs, it combines with$\mathrm{H}_2 \mathrm{O}$, forming carbonic acid \left(\mathrm{H}_2 \mathrm{CO}_3\right) . \mathrm{H}_2 \mathrm{CO}_3$ is unstable and quickly dissociates into hydrogen ions and bicarbonate ions.