Oxygen In The Blood Flashcards
What is the solubility factor for oxygen?
0.01 mmol
What is the cardiac output for the average 70kg man?
5L/min
What are the oxygen binding pigments?
Haemoglobin - tetramer (bind 4 oxygen molecules)
Myoglobin - monomer (binds 1 oxygen molecule)
What oxygen binding pigment has the highest affinity for oxygen?
Myoglobin
What is myoglobin?
Pigment found in muscles that contains haem.
It is similar to haemoglobin but has only a single subunit.
What is the shape of the myoglobin dissociation curve?
Curve is hyperbolic.
How is dissociation presented?
As a percentage
What are the two different states Hb can be in?
T - Tense - this is the low affinity for oxygen state (difficult for oxygen to bind). Occurs when pO2 is low
R - Relaxed - high affinity for oxygen (easier for oxygen to bind). Occurs when high pO2
What is the shape of the haemoglobin dissociation curve?
Sigmoidal
At what kPa is Hb saturated?
9-10kPa
At what kPa is the Hb half saturated?
3.5-4kPa
What is the oxygen content of arterial blood?
8.8mmol/L.
If anaemic, pO2 will be normal but oxygen content will be lower.
What is tissue pO2?
5kPa. But, it depends on how metabolically active the tissue it.
How low can tissue pO2 get?
Must be high enough to drive diffusion of O2 to cells.
It cannot fall below 3kPa in most tissues.
But, the higher the capillary density, the lower the pO2 can fall (as it doesn’t have to diffuse as far). Very metabolically active tissues will have higher capillary densities.
What is the Bohr shift?
When curves shifts to the right.
Decreases pH, promotes T state, give up more O2.
If pH increases - alkaline - shifts to left - R state so take more oxygen.
This is why, in metabolically active tissues, the pH is lower.
In what situation can the amount of oxygen from arterial blood that can be given up increase?
Exercise
Normally only about 27% is given up.
In extreme exercise, metabolism can increase by 10x but cardiac output only goes up by 5x
Why would 2,3-BPG increase and what happens if it is?
It increases with anaemia or at altitude
It shifts Hb dissociation curve to the right so gives up more oxygen.
How much 2,3-BPG is normally in RBCs?
5mM
When do the levels of 2,3-BPG increase?
They increase with anaemia or altitude
At what level is CO fatal?
Fatal is over 50%.
It also increases the affinity of the unaffected subunit of O2 so that oxygen won’t be given up at tissues.
What is the difference between hypoxemia and hypoxia?
Hypoxemia = low levels of oxygen in arterial blood
Hypoxia - low levels of oxygen in the body or tissues.
What is the difference between peripheral or central cyanosis?
Peripheral - hands or feet go blow due to poor local (peripheral circulation)
Central - (mouth, tongue, lips. mocous membrane) due to poorly saturated blood in systemic circulation
What is cyanosis?
Blueish colouration due to unsaturated haemoglobin.
What is pulse oximetry?
Detects level of Hb saturation of pulsatile, arterial blood.
(ignores tissues and venous blood).
It detects the difference in absorption of light between oxygenated and deoxygenated blood.
Where is arterial blood gas commonly taken from?
Radial artery
How can you calculate the amount of oxygen given up to tissues?
- Work out the fraction of oxygen given up (different in % saturation)
- Times this by 8.8mmol/L
