Carbon dioxide is transported in the blood primarily in three ways: physically dissolved (7-10%), bound to hemoglobin (20-30%), and as bicarbonate ions (60-70%). The conversion of CO2 to bicarbonate occurs in red blood cells with the help of carbonic anhydrase, facilitated by a chloride shift mechanism. The Haldane effect describes how oxygen binding to hemoglobin displaces CO2 from the blood, enhancing its release into the alveoli.

1. Transport of Carbon Dioxide

2. Diffusion of
CO2 Between
Tissue and
Capillary
Diffusion of
CO2
Between
Capillary
and Alveoli

3. • Carbon dioxide is transported in the blood
in three ways
• Physically dissolved
• Bound to hemoglobin
• As bicarbonate ion

4. Physically Dissolved
• Part of the carbon dioxide released from
the tissues is dissolved in plasma. But
only a small amount, typically just 7 –
10%, is transported this way.

5. Bound to Hemoglobin
• 30% of the CO2 combines with Hb to form
carbamino hemoglobin (HbCO2)
• The unloading of O2 from Hb in the tissue
capillaries therefore facilitates the picking
up of CO2 by Hb
• 20-30% is transported by this route

6. As Bicarbonate (HCO3) Ion
• The most important means of CO2
transport is as bicarbonate (HCO3), with
60-70% of the CO2 being converted into
HCO3 by the following chemical reaction in
Erythrocytes by the help of enzyme
Carbonic Anhydrase
C.A
• CO2 + H2O » H+ + HCO3-

8. Chloride Shift
• The red blood cell membrane has a HCO3
– Cl carrier that passively facilitates the
diffusion of these ions in opposite
directions across the membrane.
• Consequently, HCO3 efflux and Cl influx
occur, which is known as chloride shift

10. CO2 Dissociation curve

11. Haldane Effect
• binding of O2 with hemoglobin tends to
displace CO2 from the blood is known as
the Haldane effect

12. • The Haldane effect results from the fact that
• combination of O2 with hemoglobin in the lungs causes
the hemoglobin to become a stronger acid.
• This displaces CO2 from the blood and into the alveoli in
two ways.
• First, highly acidic hemoglobin has less tendency to
combine with CO2
• Second, the increased acidity of the hemoglobin also
causes it to release an excess of hydrogen ions.
• These bind with bicarbonate ions to form carbonic acid,
which then dissociates to CO2, and the CO2 is released
from the blood into the alveoli