Haemaglobin Flashcards
What is the quaternary structure of adult Hb (HbA)?
2 alpha chains
2 beta chains
tetramer structure
4 haem groups which coordinate Fe2+
What is the taute state of HbA?
Deoxygenated state when no O2 is bound
In this state there is a low affinity for O2 binding until the first O2 is bound, when the affinity exponentially increases
What is the relaxed state of HbA?
When all 4 haem sites are occupied by O2
This is when O2 is most likely to dissociate
Binding of O2 occurs via cooperative binding
How does the binding of the first O2 result in binding of remaining O2 molecules?
Process called positive cooperativity
Binding of first O2 mediates conformational change
This forces HbA into a structure where less energy is needed to bind 3x remaining O2
What are the 3 main ways by which CO2 is transported in the body?
bound to Hb (75%)
dissolved in plasma (25%)
buffered with water -> HCO3- (10%)
Why is the conversion of CO2 to HCO3- (and vice versa) in plasma slow? What does this say about plasma’s inherent role in buffering the blood?
No carbonic anhydrase present extracellularly
So conversion between H20 and HCO3- itself is slow
This means that plasma inherently contributes very little to the blood buffering systems
Which law applies to the solubility of CO2 in plasma?
Henry’s Law
number of molecules in solution is proportional to the partial pressure of that molecule at liquid surface
What is the relative solubility of CO2 compared to O2 in plasma?
CO2 is 20x more soluble than O2
What is the relationship between temperature and solubility?
Solubility increases as temperature falls
i.e an inverse relationship
What are the partial pressures of CO2 in blood vessels?
venous blood: 6.1kPa
arterial blood: 5.3kPa
What are the properties of pCO2 in alveoli? How does this affect gas exchange?
high solubility
high diffusing capacity
-> this means that CO2 is readily excreted via airways (breathing out) and easily dissolved in the water vapours within alveoli prior to this
What is the Henderson-Hasselbach equation?
CO2 + H2O -> H2CO3 -> HCO3- + H+
first reaction is reversible and is catalysed by carbonic anhydrase
What are the relative concentrations of H2CO3 and HCO3- in the blood? (physiologically)
1 mole of H2CO3 for every 20 moles of HCO3-
What is found in a blood film after splenectomy or in hyposplenism?
Howell-Jolly bodies Pappenheimer bodies Poikilocytes (Target cells) Erythrocyte containing siderotic granules Heinz bodies
What are stipple cells associated with?
Found in blood film in lead poisoning or in haemaglobinopathies
also known as basophilic stippling
