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Question: The bulk of carbon dioxide \[\left[ {C{O_2}} \right]\] released from body tissues into the blood is ...

The bulk of carbon dioxide [CO2]\left[ {C{O_2}} \right] released from body tissues into the blood is present as
A. Bicarbonate in blood plasma and RBCs
B. Free CO2C{O_2} in blood plasma
C. 70%70\% carbamino haemoglobin and 30%30\% as bicarbonate
D. Carbamino haemoglobin in RBCs

Explanation

Solution

The exchange of respiratory gases occurs at the cellular and the alveolar layers in the human body. The oxygen is carried towards the cells and the carbon dioxide is taken out from the cells. Moreover, the carbon dioxide reacts with the water of the plasma and RBCs to form the carbonic acid which dissociates into the protons and bicarbonate ions.

Complete answer: The gaseous exchange at the cellular layer:
The carbon dioxide transports in three forms to the cells -
1. In the form of carbonic acid: Seven percent of the carbon dioxide reacts with the water of the plasma to form the carbonic acid. This carbonic acid later dissociates and passes out through the urine.
2. In the form of bicarbonate ions: Seventy percent of the carbon dioxide reacts with the water of the red blood cells to form the carbonic acid in the presence of the carbonic anhydrase enzyme. This carbonic acid dissociates into the protons and the bicarbonate ions respectively. These bicarbonate ions participate in the Hamburger’s process of chloride shift or the Hamburger’s phenomenon.
3. In the form of carbamino haemoglobin: Twenty-three percent of the carbon dioxide transports in the gaseous form and reacts with the haemoglobin to form the complex of Haemoglobin and carbonic acid. In the RBCs, the dissociation of the oxyhemoglobin occurs on the cellular layer. In the plasma the Sodium Bicarbonate forms, which is then excreted out of the urine.
4. The gaseous exchange at the alveoli layer: The deoxygenated blood reaches the alveoli layer with the haemoglobin-carbonic acid complex in the RBCs. Ninety-seven percent of the oxygen diffuses in the gaseous form while the three percent remains dissolved in the plasma.
Thus, based on the above information we can conclude that the bulk of Carbon dioxide [CO2]\left[ {C{O_2}} \right] released from body tissues into the blood is present as Bicarbonate in blood plasma and RBCs.
Hence, the correct answer is option (A).

Note: The shifting of the bicarbonate ions outside and chloride ions inside is known as the chloride shift or the Hamburger’s process. Due to the protons, the splitting of the oxyhemoglobin occurs, but the high concentration of the bicarbonate ions could coagulate the red blood cells. Therefore, to maintain the ionic equilibrium of the red blood cells, the chloride ions from the sodium chloride of the plasma dissociates and shift into the red blood cells and in turn, the bicarbonate ions dissociate into the plasma. This process is known as the chloride shift of Hamburger’s phenomenon.