Lecture 17 Flashcards
Why do we need haemoglobin to transport oxygen?
Oxygen isn’t very dissolvable in blood (only 0.03 ml of oxygen per litre of blood for each mmHg), this makes it very ineffective for oxygen transport and instead we must use haemoglobin to carry the oxygen.
Describe oxygen’s reaction with haemoglobin.
Oxygen forms an easily reversible combination with haemoglobin to give oxyhaemoglobin. The binding depends on the partial pressure of oxygen (binds in lungs where this is high, unbinds when in places which need oxygen where this is lower), this leads to a disassociation curve with saturation.
Describe the oxygen saturation curve for haemoglobin. What are the advantages of this curve?
Oxygen saturation tells us how full the haemoglobin is, it is the percentage of the available binding sites on haemoglobin which have O2 attached, for venous blood this is roughly 75% for arterial blood it is roughly 95-100%. At 25mmHg the Haemoglobin is 50% saturated. Overall this is a sigmoidal relationship (not linear).
The advantages of the sigmoidal curve shape are: the steep part means a small change in partial pressure of oxygen will lead to a big change in saturation, particularly good during exercise, the flat part means that we have a large reserve of extra oxygen.
What is oxygen capacity? How do we calculate it and what are some common values?
How is it related to oxygen content?
Oxygen capacity tells us how much oxygen the blood could carry, it is the maximal amount of oxygen that can be combined with haemoglobin (100% saturated), typically there is roughly 150 g of haemoglobin per litre of blood and one gram can combine with 1.34 ml of oxygen (leading to 200 ml of oxygen per litre of blood (150 g x 1.34)).
Oxygen content is the capacity x the saturation out of 100 + the dissolved oxygen (0.03 x partial pressure of oxygen).
What is the graph of oxygen content vs partial pressure of oxygen like?
The curve of oxygen content is essentially the same as the percent haemoglobin concentration.
What is the arteriovenous difference and what does it tell us? What occurs to this during exercise and why?
The arteriovenous difference is the difference between arterial oxygen content and venous oxygen content, this value tells us how much blood made it into the tissues.
During exercise this value will increase because the partial pressure of oxygen will be lower in the venous blood.
What occurs to an anaemic person’s saturation and oxygen content curve? What does this mean for exercise and rest?
For anaemic people the saturation curve remains roughly the same (slight decrease, but nothing major), however the oxygen content is very reduced due to the much lower haemoglobin amount, meaning they can’t supply enough oxygen during exercise (at rest they are normally fine).
What does carbon monoxide do to oxygen content?
Carbon monoxide will combine with haemoglobin to form carboxyhemoglobin, blocking oxygen binding sites due to having 250 times more affinity for haemoglobin. This means small amounts can tie up a large proportion of the haemoglobin in the blood and hence shifting the oxygen content curve to the left and making it more difficult to unload oxygen due to changes to the saturation curve.
What occurs to the haemoglobin saturation curve in different locations? What kind of molecules do this?
Haemoglobins saturation curve varys with conditions (carbon dioxide, H+, 2,3 biphosphoglycerate( diphosphoglycerate is the same thing) and temperature all lower oxygen affinity to release the oxygen in tissues which need it, (right shift in saturation graph)). This means it has high oxygen affinity in the lungs and low in the muscles and also unloads more during exercise. This is known as the Bohr effect.
What factors increase 2,3 diphosphoglycerate production?
2,3 DPG is a by product of glycolysis, it increases with intense exercise, high altitude and due to severe lung diseases.
How is carbon dioxide transported in the blood?
Carbon dioxide is twenty times more soluble ithat oxygen (10% of the amount in the blood), also as bicarbonate ion (which will be converted to carbon dioxide in the lungs) (70%) and also combined with proteins are carbamino compounds (typically with haemoglobin on terminal NH2 groups, this is easier when it isn’t bound to oxygen, this is due to haemoglobin being in a reduced form, HHb (which also further pushes the carbon dioxide to bicarbonate reaction), this is known as the Haldane effect)(20%).
Once the lungs are reached the high oxygen concentration pushes the haemoglobin out of the carbamino form.
