3.1.2j) The oxygen dissociation curve for fetal and human haemoglobin Flashcards
(9 cards)
Oxygen dissociation curve
The percentage saturation haemoglobin in the blood is plotted against the partial pressure of oxygen (pO₂)
Shows the affinity of haemoglobin for oxygen
Curve levels out at the highest partial pressure as all haem groups are bound to oxygen - haemoglobin is fully saturated
Bottom portion of curve
At low pO₂, few haem groups are bound to oxygen - so haemoglobin does not carry much oxygen
Middle portion of curve
At higher pO₂ more haem groups are bound to oxygen making it easier for more oxygen to be picked up
Top portion of curve
The haemoglobin becomes saturated at very high pO₂ as all the haem groups become bound
Bohr shift (the effect of carbon dioxide)
As the partial pressure of CO₂ rises (higher partial pressure of CO₂) - haemoglobin gives up oxygen more easily
Bohr effect is important in the body
Active tissues - with a high partial pressure of CO₂, haemoglobin gives up O₂ more easily
In the lungs - proportion of CO₂ in the air is relatively low, O₂ binds to the haemoglobin molecules
Fetal haemoglobin
Fetus is dependent on the mother to supply it with O₂
Oxygenated blood from the mother runs close to the deoxygenated fetal blood in the placenta
Fetal blood has higher affinity for O₂ (at every point of the curve) to transfer O₂ to the fetus
Fetus removes O₂ from the maternal blood as they move past each other
Transporting carbon dioxide
5% - carried dissolved in the plasma
10-20% - combined with the amino groups in the polypeptide chains of haemoglobin (Carbaminohaemoglobin)
75-85% - converted into hydrogen carbonate ions in the cytoplasm of RBC
Carbonic acid reaction
CO₂ reacts slowly with water to form carbonic acid
Carbonic acid then dissociates to form H+ ions & hydrogen carbonate ions
Takes place in the blood plasma
In the cytoplasm of RBCs - high levels of carbonic anhydrase (catalyses the reversible reaction)
