16 carriage of O2 Flashcards
In what 2 ways is oxygen carried in the blood?
dissolved in plasma
bound to haemoglobin in RBC’s
How is there a relationship between PO2 and Hb saturation?
only the dissolved O2 exhibits partial pressure, this then dictates the degree to which O2 binds to haem.
What is Henry’s Law?
dissolved O2 = partial pressure x solubility coefficient (0.225 for O2)
What does haemoglobin offer?
Additional carrying capacity
Why can’t there be 100% oxygen in our lungs?
because there is also H2O and CO2
What is the structure of haemoglobin?
In each haem there is iron, which the O2 binds to. The haem structure then binds to one of 4 polypeptides (globin)
What is O2 content measuring?
quantity of dissolved and haem associated O2 in a given volume
What is O2 capacity measuring?
maximum amount of O2 that can combine with haem in blood (independent of partial pressure)
What is Hb saturation measuring?
ratio of quantity of O2 combined with Hb in a given sample to the O2 carrying capacity of that sample
What does the steep part of the haem dissociation curve represent?
dissociation, ensuring adequate delivery of O2 to tissues, maintaining high PO2 levels, so it diffuses in
What does the flat part of the curve represent?
association
ensures almost complete loading of Hb despite fluctations in PO2
How can the curve be shifted right, and why would we want to shift the curve right in these conditions?
increased CO2 decreases pH increasing temp 2,3-DPG conc autoregulated delivery, the amount of O2 delivered depends on how far the curve shifts right
What effect does the Bohr effect have on the lungs?
none, as this is in the flatassociation bit
What effect on the curve does ventilation have?
none, it only affects PaO2
What effect does CO have on Hb?
it has 210x the affinity as O2 does, so very little is required to minimise O2 carring capacity
Why is CO poisoning fatal when anaemia isnt?
in CO poisoning O2 isn’t released from Hb until the PO2 is fatality low, due to change in the Hb curve
What is adult haemoglobin comprised of?
98% HbA 2xalpha, 2xbeta
2% HbA(2) 2xalpha, 2xdelta
What is type F haemoglobin comprised of?
2xalpha, 2xgamma
What is the functional difference between adult and foetal haemoglobin?
type F has a much lower affinity for O2, so curve shifted to the left
What effect does 2,3-dpg have on type F?
decreases affinity og haem for O2, releasing ti to the surrounding tissues
Why is the low affinity for O2 beneficial for the foetus?
because arterial PO2 is low
What is methemoglobinaemia?
ferrous Fe2+ oxidised to Fe3+, ferric haem can’t bind to O2
What is myoglobin?
O2 storage in muscles with 1 haem group, curve shifted left of haemoglobin
What are the 4 types of hypoxia?
hypoxic hypoxia
anaemic hypoxia
stagnant hypoxia
histotoxic hypoxia
What is stagnant hypoxia?
low perfusion due to shock (like cardiac failure)
What is histotoxic hypoxia?
inability of tissues to utilise O2, so it just returns in venous blood
