Question

Describe how CO2 is transported in the blood stream and how this is different than O2 transport.

Answer 1

Answer:

Introduction: Carbon dioxide is a gas which is more soluble in the blood as compared to that of the oxygen. The percentage of the carbon dioxide in the atmosphere is around 0.03% whereas the same is produced within the body tissues as a result of the metabolism and its partial pressure is around 45 mm of Hg. This clearly signifies that the concentration of Co2 within the body is more as compared to that of the atmosphere and henceforth we exhale CO2. The exhalation pathway is as follows:

Body tissues-lungs-bronchioles-bronchi-trachea-larynx-pharnynx-nostrils

There are three mechanisms for the transportation of CO2 from the body tissues till the lungs. They are as follows:

Mechanism of CO2 transport:

1. In the dissolved state: Since CO2 is more soluble as compared to that of the oxygen, a relatively higher percentage of CO2 gets transported in this form. A total of 7 % of CO2 gets transported by getting dissolved in the blood plasma

2. In the form of bicarbonate ions: Nearly 70 % of the total CO2 gets transported to the lungs in the form of bicarbonate ions. Their formation takes place on the surface of the RBCs because of the presence of the enzyme named Carbonic anhydrase on the surface of RBC. The mechanism is as given below:

CO2+H2O forms carbonic acid (H2CO3) on the surface of RBC in the presence of enzyme; Carbonic anhydrase.

However carbonic acid is a weak acid and it readily gets dissociated to form H+ ions and HCO3- ions (bicarbonate ions).

These bicarbonate ions then diffuse out of the RBC to the plasma due to the concentration gradient. However in return, it gets compensated by the movement of chloride ions in order to maintain the ionic balance. This process is called as chloride shift.

3. As carbaminoglobin: Nearly 23% of the CO2 gets bound to the NH2 portion of the hemoglobin present within the RBC of the blood. The product thus formed is called as the carbaminaglobin. It is represented as HbCO2. However, this product also is a very unstable product and it readily gets dissociated to yield CO2 after reaching the alveoli of the lungs.

Thus, these are the different methods of transportation of CO2 to the lungs from the various body parts. These transportation methods differ from that of oxygen in two ways;

a) Oxygen is less soluble in plasma as compared to CO2. Therefore as against 7% (case of CO2), only about 3% of oxygen gets transported in a dissolved state

b) There are only two ways of transport of oxygen from lungs to the different body tissues; first being the dissolved plasma state and the second being the oxyhemoglobin formation that is around 97 % of the oxygen gets bound to the hemoglobin to yield oxyhemoglobin leading to their delivery within the different body tissues.