Download Oxygen Transport Notes

Carbon Dioxide Transport Notes
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Carbon dioxide cannot be allowed to accumulate in the blood as the acid it forms could
lead to fatal changes in pH.
Can be carried in 3 ways:
1) In solution (5%)
2) Combined with protein (10-20%) Carbon dioxide combines with the amino group at the
end of each polypeptide chain of haemoglobin to form a neutral CARBAMINOHAEMOGLOBIN compound. The amount carried like this depends on the amount of
oxygen already being carried by the haemoglobin molecule.
3) As hydrogencarbonate (85%) Carbon dioxide diffuses into blood stream and into red
blood cells. Here, it combines with water to form carbonic acid, using the enzyme
CARBONIC ANHYDRASE (found in red blood cells). Some carbonic acid then
dissociates into ions. What happens to the hydrogen ions? Think back to your
notes on oxygen transport. By accepting lots of hydrogen ions, haemoglobin acts as
a pH buffer allowing large quantities of carbonic acid to be transported to the lungs
without any major change in blood pH. The remaining hydrogencarbonate ions diffuse
out of the red blood cell into the plasma along a concentration gradient. Here they
combine with sodium to form SODIUM HYDROGENCARBONATE. The loss of the –ve
hydrogencarbonate ions from the red blood cell leaves then positively charged.
Negative chloride ions therefore diffuse into the red blood cell to balance the charges.
This is known as the CHLORIDE SHIFT.