Transport of oxygen and CO2 in the blood 8.4 Flashcards
How are erythrocytes specialised?
No nucleus which helps store maximum amounts of haemoglobin
Its biconcave shape which increases surface area and helps them squeeze through the small capillaries
They are formed continuously in bone marrow
How do erythrocytes bind to oxygen?
They contain haemoglobin which is a conjugated protein made of 4 subunits, each one containing an iron haem prosthetic group. It can bind to 4 oxygen molecules
Haemoglobin + Oxygen
Hb + 4O2 Oxyghaemoglobin Hb(O2)4
It’s reversible
How is oxygen picked up?
When erythrocytes travel around the alveoli, they have low oxygen conc compared to the alveoli, so oxygen will diffuse in and an oxygen molecule will bind to the haemoglobin. This will change the shape of it which will make it easier for the rest of the oxygens to bind to it. When the oxygen is bound, the oxygen conc in the erythrocyte will still be low, so the rest of the oxygens will enter the same way until the haemoglobin is saturated.
How is oxygen released?
When the erythrocytes travel to the cells that need the oxygen, there is a high oxygen conc on the inside of the erythrocyte compared to inside the cell, so the oxygen will be removed from the haemoglobin. This then changes the shape of the haemoglobin again so it is easier for oxygen to be removed, and this will continue until all the oxygen is gone.
Partial Pressure
It’s how the concentration of a mixture of gases will change over time. For example, in an airtight room, the amount of air will not change but the partial pressure of oxygen will decrease and the partial pressure of co2 will increase as you breathe.
Oxygen Dissociation Curve
Shows how oxygen is transported by the blood. The % saturation of haemoglobin is plotted against the partial pressure of oxygen so will show how the haemoglobin binds to the oxygen.
Explaining the oxygen dissociation curve
At the bottom, if the partial pressure of oxygen is low, the haemoglobin won’t be bound to too much oxygen so won’t be transporting a lot. If the partial pressure of oxygen started increasing, then the curve would sharply start increasing as the haemoglobin would bind to oxygen moe easily so more would be bound to oxygen. Then as the partial pressure gets even higher, the curve will level off as the haemoglobin will be saturated and can’t take up any more
Bohr Effect
As the partial pressure of CO2 increases, the easier it is for haemoglobin to give up oxygen which is known as the Bohr Shift. The curve is moved to the right. This is useful because in tissues with high CO2 partial pressure, oxygen can be given up more easily so gas exchange can occur faster
Fetal Haemoglobin
When the fetus is developing, it’s completely dependent on its mother for oxygen. The mother’s oxygenated blood will travel to the fetus with deoxygenated blood and because the fetal haemoglobin has a higher affinity for oxygen it will take it up easier so the curve will be moved to the left.
How is carbon dioxide transported in the body?
5% is transported in the plasma and dissolved
20% is combined with the amino acids in haemoglobin to make carbaminohaemoglobin
75% reacts with water in the erythrocytes to make carbonic acid which then dissociates into hydrogen ions and hydrogen carbonate ions which is catalysed by carbonic anhydrase in the erythrocytes.
Chlorine Shift
When the hydrogen carbonate ions have been made in the erythrocyte, they will diffuse out into the blood and chloride ions will move into the erythrocyte which will maintain the electrical balance. This also means that more CO2 will diffuse into the erythrocytes as the CO2 gets converted so there’s a low conc inside.
What happens when carbon dioxide has to be released?
When the erythrocyte reaches the lungs where there is a low amount of CO2, the carbonic anhydrase will break down carbonic acid into Co2 and water again and the Co2 will diffuse into the lungs. The chloride will also diffuse out back into the blood.
How does haemoglobin act as a buffer?
It maintains the pH by accepting any extra hydrogen ions to produce haemoglobinic acid
