Flashcards in 8.4 Transport of CO2 and O2 In The Blood Deck (13):
What is haemoglobin? Describe its structure
A large protein with a quaternary structure - it’s made up of four polypeptide chains.
Each chain has a haem group which contains iron and gives haemoglobin its red colour.
It is carried around by red blood cells.
Where are how is oxyhaemoglobin formed?
In the lungs, oxygen joins to the iron in the haemoglobin to form oxyhaemoglobin.
Hb + 4O2 ( reversible reaction ) HbO8
This is a reversible reaction - when oxygen dissociates from oxyhaemoglobin near the body cells, it turns back to haemoglobin
How many oxygen molecules can haemoglobin carry?
What does partial pressure of oxygen mean?
Measure of oxygen concentration
How does haemoglobins affinity for oxygen change in different partial pressures?
Oxygen loads onto haemoglobin ( high affinity) to form oxyhaemoglobin where there’s high partial pressures of O2.
Oxyhaemoglobin unloads it’s oxygen ( low partial pressure ) where there’s a low partial pressure of O2.
Describe how haemoglobin acts at the lungs and at respiring cells?
Oxygen enters blood capillaries at the alveoli in the lungs.
Alveoli have a high partial pressure of oxygen, so oxygen loads onto haemoglobin to form oxyhaemoglobin.
When cells respire, they use up oxygen and this leads to a lower partial pressure of oxygen.
Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads it’s oxygen .
It then returns to the lungs to pick up more oxygen.
Explain why dissociation curves are shaped the way they are
It is S shaped because when Hb combines with the first O2 molecule, it’s shape alters in a way that makes it easier for other molecules to join too.
As the Hb gets more saturated, it gets harder for more oxygen molecules to join.
As a result, the curve has a steep bit where it’s really easy for oxygen to join and a shallow bit at each end where it’s harder.
When the curve is steep, a small change in pO2 causes a big change in the amount of oxygen carried by the Hb.
How is fetal haemoglobin different from adult haemoglobin ?
It has a higher affinity for oxygen than adult haemoglobin at the same partial pressure.
Why is fetal haemoglobin different?
It gets oxygen from its mothers blood across the placenta.
This blood has a low partial pressure of oxygen because some had been used up by the mother already.
Therefore it needs to have higher affinity to get enough oxygen to survive.
How does haemoglobins affinity for oxygen change at different partial pressures of CO2?
Haemoglobin gives up it’s oxygen more readily at higher partial pressures of CO2.
Describe how the carbon dioxide produced in respiring tissues dissociates and travels to the alveoli
At respiring tissues :
CO2 and water combine to form carbonic acid ( catalysed by carbonic anhydride )
Carbonic acid dissociates into H+ ions and HCO3- ions
Increase in H+ causes oxyhemoglobin to unload it’s oxygen so that haemoglobin can take up the H+ ions, forming haemoglobinic acid.
HCO3- ions diffusion out of the red blood cells and are transported in the blood plasma.
At lungs :
The low pCO2 causes some of the HCO3- and H+ ions to recombine into CO2 and water.
The CO2 then diffuses into the alveoli and is breathed out.
What is the chloride shift?
To compensate for the loss of HCO3- ions from the red blood cells, chloride (cl-) ions diffuse into the red blood cells.
This maintains the balance of the charge between the red blood cell and the plasma.