Transportation.of CO2 in blood, 3 main forms-
1. Dissolved CO2
About 7 % CO2 is dissolved In plasma, reaching the lungs, it diffuses into alveoli
2. Carbaminohemoglobin
About 20-25 % is combine with hemoglobin to form Carbahemoglobin.
Hb+CO2- HbCO2
Haemoglobin carbondioxide carbaminohemoglobin
In tissue capillaries PCO2 is high and promotes formation of carbamino-Hb but in pulmonary capillary PCO2 is high.
3. Bicarbonate ions
About 70% CO2 is transmitted in plasma and RBC as bicarbonate ion (HCO3-).
CO2 diffuses into tissue capillaries and enters erythrocytes, it reacts with water in presence of enzyme carbonic anhydrase (CA), to form carbonic acid (H2CO3).
The carbonic acid dissociates into H+ and HCO3- (bicarbonate ion)
Many of H+ combine with haemoglobin-H.Hb
HCO3- accumulates inside erythrocyte, diffuses into plasma.
In exchange, chloride ions (cl-) diffuse from plasma into erythrocytes.
This exchange of negative ions maintain electrical balance between plasma and erythrocytes.
Carbondioxide and pH
CO2 - pH (acidic)
CO2- pH (alkaline)
Hb lower affinity for oxygen secondary to increase in partial pressure of CO2 / or decreased blood pH.
This lower affinity enhances uploading of oxygen into tissue to meet oxygen demand of tissue.
Function of Hemoglobin - transport oxygen
High contraction of CO2- in tissue cell
High contraction of O2 - in lungs
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