Modifications of Oxygen transport and carriage of carbon dioxide Flashcards
what is Methaemoglobin?
Methaemoglobin is produced when the haem group is oxidised from Fe2+ to Fe3+ either spontaneously or as a side effect of certain drugs such as nitrates and sulphonamides.
Methaemoglobin cannot bind or transport O2.
How are levels of Methaemoglobin controlled?
Methaemoglobin levels are kept at around 1.5% of total haemoglobin by the enzyme Methaemoglobin reductase.
what is the result of methaemoglobin reductase deficiency?
deficiency in the methaemoglobin reductase enzyme can allow methaemoglobin levels to build up to up to 25% –> 25% reduction in O2 carrying capacity
what reducing agents can be used therapeutically to reduce methaemoglobin?
Vitamin C and methylene blue can be used to reduce methaemoglobin therapeutically.
what leads to the formation of glycosylated Hb?
a high plama concentration of glucose can lead to the formation of covalent bonds between glucose and beta chains of Hb. This leads to the formation of glycosylated Hb (HbA1c)
The amount of HbA1c is linked to….
mean blood glucose concentration
what is the effect of glycosylation on O2 carriage?
glycosylation has no direct impact on oxygen carriage.
what is a high HbA1c an indicator of?
poor diabetic control; HbA1c is an index of the mean plasma glucose over the life of the erythrocyte (about 120 days)
what is normal level of HbA1c?
normally 4-6% of Hb is glycosylated- levels higher than 7.5% may indicate a problem. This is used to assess the adequacy of long term blood glucose regulation in diabetes.
what is cyanosis?
cyanosis is inadequate oxygenation of the blood, but it is not necessarily hypoxia; it is characterised by high levels of deoxyhaemoglobin which are blue/ purple in colour. Most textbooks say 5g/100ml of deoxyhaemoglobin
what are the two forms of cyanosis? Describe them.
the two forms of cyanosis are central and peripheral cyanosis. Peripheral cyanosis is poor tissue perfusion leading to increased oxygen extraction from available blood. central cyanosis is poor oxygenaation of blood in the lungs.
how is central cyanosis seen?
cyanosis of the tongue- central and easy to see/ access
What is Raynaud’s disease?
Raynaud’s disease is when the peripheral arterioles constrict excessively in response to cold- in particular the fingers may appear white and feel numb. In extreme cases, there may be local ischaemia and tissue damage. when bloodflow is restored, the fingers flush red and the sufferer experiences considerable pain.
who is more likely to suffer from cyanosis: a person with polycythaemia or an anaemic person?
a person with polycythaemia because if they have more RBCs and more Hb- this haemoglobin is less likely to be saturated than that of an anaemic person who has lower amounts of Hb.
Describe the relationship between haemoglobin and CO.
The haem group of haemoglobin is not specific for O2, it will bind other substances such as CO. Hb has an affinity for CO that is 200 x greater than the affinity for O2. Hb cannot bind both simultaneously and so will bind CO preferentially, giving carboxyhaemogolobin. Carboxyhaemoglobin is cherry red in colour- pulse oximeters will give a normal reading.
