Respiration is the process through which living organisms take in oxygen and give out carbon dioxide to release energy. So, naturally, respiration is a major and vital process of gas exchange. The transport of gases during respiration, both oxygen and carbon dioxide are carried out by the blood cells.
The transportation of gases is a very efficient process. Let us now see how oxygen and carbon dioxide is transported in the human body.
Transport of Oxygen
During respiration, about 97% of oxygen is transported by Red Blood Cells in the blood and the remaining 3% gets dissolved in the plasma. Haemoglobin transports oxygen molecule to all the body cells for cellular respiration. The haemoglobin pigment present in the blood gets attached to O2 molecules that are obtained from breathing and thus forms oxyhaemoglobin. This oxygenated blood is then distributed to all the body cells by the heart. After giving away O2 to the body cells, blood takes away CO2 which is the end product of cellular respiration and blood becomes de-oxygenated.
Transport of carbon dioxide
Since haemoglobin pigment has less affinity for CO2, CO2 is mainly transported in the dissolved form. This deoxygenated blood gives CO2 to lung alveoli and takes O2 in return. Around 20-25% of carbon dioxide is carried by haemoglobin as carbamino-haemoglobin. 7% is in a dissolved state in the plasma and the remaining is carried as bicarbonate. Again, the binding of carbon dioxide with haemoglobin is related to the partial pressure of carbon dioxide, and the partial pressure of oxygen. As mentioned earlier, the partial pressure of carbon dioxide is high in the tissues and this is where more binding of carbon dioxide occurs. In the alveoli where the partial pressure of oxygen is high, carbon dioxide gets dissociated from carbamino-haemoglobin. The enzyme carbonic anhydrase present in a high concentration in RBCs, and in small quantities in the plasma, facilitates this reaction in both the directions. So, the bicarbonate formed at the tissues releases carbon dioxide at the alveoli.