Session 4 Flashcards
What is important about myoglobin?
In muscle
It saturates at low pO2
13.3 kPa and above it is 100% saturated
What state of haemoglobin binds O2 well?
Relaxed
What state of haemoglobin binds O2 poorly?
Tense
At what pO2 is haemoglobin saturated?
8.5 kPa
At what pO2 is haemoglobin unsaturated?
1 kPa
At what pO2 is haemoglobin half saturated?
3.5-4 kPa
What is the pO2 in the lungs?
13.3 kPa so haemoglobin is well saturated
What is the oxygen content in normal blood?
2.2 mmol/L and each haemoglobin molecule binds 4 O2 so 8.8 mmol/L actually in blood
Approximately, what is tissue pO2?
5 kPa so haemoglobin would be around 65% saturated.Cannot fall below 3 kPa, but the higher the capillary density the lower it can fall
How can you calculate the amount of O2 given up at the tissues?
100% saturation of Hb goes to 65% so 35% change. 8.8 mmol/L x 0.35 = 3 mmol/L
What effect does pH have on the state of haemoglobin?
Acid - Tense
Alkali - Relaxed
How does the pH of tissues aid O2 delivery?
It is lower so haemoglobin becomes tense and dissociates extra O2
What effect does temperature have on haemoglobin?
It puts it into its tense state
What is maximum unloading?
Haemoglobin becomes very tense and gives up around 70% of O2 due to the higher temperature and lower pH
What is O2 reserve?
73% of O2 stays in the blood so if extra O2 needs to be used it can. This is important as muscle activity can increase higher than the cardiac output can safely (So not enough O2 would be able to reach the tissues without O2 reserve)
What does CO2 react with in the blood?
Water to make H+ and HCO3-
Reversible reaction and amount reacting depends on the concentration of reactants and products
What does dissolved CO2 depend on?
pCO2. So if pCO2 rises, pH will fall. If pCO2 falls, pH will rise
What is the other source of HCO3-? (Not CO2)
From NaHCO3. This keeps HCO3- concentration high enough to prevent all CO2 dissolving. Keeps pH alkaline
What does H+ from the reaction of CO2 and H2O do?
Bind to haemoglobin (Means there is less space for O2)
Why doesn’t the concentration of HCO3- vary much with pCO2?
Because the reactions of CO2 in the red cell are mainly controlled by how much H+ binds to haemoglobin
What happens when the body produces acid?
It will react with HCO3- (to buffer) and form CO2 which can be breathed out (prevents a large change in pH)
Does more CO2 dissolve in venous blood or arterial blood?
Venous as the pCO2 is higher, but amount of O2 bound effects it as if more O2 is bound, there is less space for CO2
What happens when there is extra CO2 in the venous blood?
More is converted to HCO3-
More H+ bind haemoglobin
When reaches lungs, O2 replaces H+ which reacts with HCO3- to make CO2 and is breathed out.
This prevents pH rising as both CO2 and HCO3- rises so ratio is the same
What is a Carbamine compound?
CO2 can bind directly to proteins and these contribute to CO2 transport, but not acid/base balance
