pk 6 - Carriage of O2 Flashcards
The carriage of O2 around the body is crucially dependent upon the Hb concentration for …… and PaO2 for …………..
capacity
diffusion
In what two ways is O2 carried in the blood?
Which of these contributes to partial pressure?
What determines the combination of O2 with Hb?
There is therefore a relationship between Hb ………… and ….. and therefore also with O2 …………..
physically dissolved in plasma solution
chemically bound to Hb in RBC’s
Partial pressure exerted by dissolved O2 only
The combination with Hb is determined by the partial pressure
saturation, PO2, content
What determines how much O2 is dissolved in a physical solution? Who’s law is this?
Henry’s Law
Dissolved O2 = partial pressure x solubility coefficient
What is the structure of haemoglobin?
4 haem groups bind to one of 4 polypeptide chains to make 1 Hb molecule
2 alpha chains, 2 beta chains
What is cooperative binding?
Once one molecule of O2 has bound to a haem group, the subsequent binding of O2 to that Hb molecule is easier
What is a normal blood Hb per litre?
147g
Define oxygen content.
Define oxgen capacity.
Define Hb saturation.
Content = quantity of O2 in a given sample of blood. Dissolved plus bound Capacity = the max quantity that can bind with Hb, this is independent of partial pressure Saturation = ratio of quantity of O2 combined with Hb to the O2 capacity of that sample, %
What oxygen at 100% Hb saturation equal to?
oxygen capacity
What is the significance of the two parts of the Hb dissociation curve?
Flat, Association part ensures complete loading of Hb despite potential small changes in PO2
Steep, Dissociation part ensures adequate delivery of O2 to tissues whilst still maintaining arterial PO2 levels high
By what 3 mechanisms can the Hb dissociation curve be shifted right?
- increasing PCO2/decreasing pH
- increasing temperature
- increasing 2,3-DPG concentration
2,3-DPG side reaction of ………. . Levels increase with ……… …….. and decrease with ………. / ………. … ……….. ……….
glycolysis
chronic hypoxia
acidosis / storage in blood banks
What factors can affect O2 capacity?
Describe the shape of the curve in anaemia if plotted against oxygen content.
Why would there be no change in the shape of the Hb curve if plotted against saturation?
dietary e.g. iron deficiency
reduced RBC count - anaemia
CO poisoning
Same shape just lower oxygen content
No change because capacity is low but ability to deliver O2 has not changed
What measure can help us define a shift of the Hb dissociation curve?
P50
Why is losing 50% Hb in CO poisoning fatal but is not in anaemia?
The shape of the curve has changed with CO poisoning.
It is now a rectangular hyperbola.
In CO poisoning O2 is not released from Hb until the PO2 is fatally low
How is foetal Hb different to adult Hb and why is this important?
2alpha2gamma - slightly less affinity for O2
BUT has considerably less affinity for 2,3-DPG so the curve is shifted left - beneficial when arterial PO2 is low
