How are respiratory gases transported in human blood

Transport of respiratory gases in the blood:

Blood is the medium of transport for O₂ and CO₂.

(i) Tranport of oxygen

- About 97% of the oxygen is transported by the erythrocytes in the form of

oxyhaemoglobin and 3% is carried in a dissolved form in the plasma.

- Oxygen binds with the Fe²⁺ part of the haemoglobin in a reversible manner to

form oxyhaemoglobin.

- Each haemoglobin molecule can carry a maximum of four molecules of oxygen.

(ii) Transport of carbon dioxide

- About 4 ml of carbon dioxide is transported by 100 ml of blood.

It is transported in three forms:

(i) In the dissolved form in the plasma (5-7%).

(ii) As bicarbonates in the plasma and in the erythrocytes (70%).

(iii) As carbaminohaemoglobin in the erythrocytes (23%).

- In the erythrocytes, carbonic anhydrase catalyses the formation of bicarbonates

from carbon dioxide and water.

- Most of the bicarbonates leak out into plasma in exchange of Cl^- ions.

- In the plasma CO₂ is carried in the form of sodium bicarbonate while in the

erythrocytes, as potassium bicarbonates.

- Some CO₂ combines with the amine radical of globin part of haemoglobin and

forms carbaminohaemoglobin.