Week 4 - Oxygen Flashcards
What is the solubility of oxygen?
Less soluble than carbon dioxide
0.01 mmol/KPa
What is the calculation for the concentration of dissolved oxygen?
Solubility X pO2
What is the normal pO2 in the lungs?
13.3 kPa
What is the amount of dissolved oxygen at a pO2 of 13.3 kPa?
0.13 mmol/L
How much oxygen does the body need?
At rest 12 mmol per minute
What features must oxygen carriers have?
Reaction needs to be reversible
Oxygen must dissociate at the tissues to supply them
What are the oxygen binding pigments found in the body called?
Haemoglobin and myoglobin
Describe the main features of haemoglobin?
Present in blood
Tetramer - binds 4 oxygen molecules
What are the main features of myoglobin?
Present in muscle cells
Monomer - binds 1 molecule of oxygen
What is a dissociation curve?
Plotted bound oxygen against pO2
Why does the curve plateu?
The is limited pigment so it saturates
What does the amount of bound oxygen depend on and how is this issue overcome?
Depends on amount of pigment
Overcome by expressing saturation as a percentage
Is myoglobin or haemoglobin saturation curve steeper?
Myoglobin - saturates at a much lower pO2
Describes the 2 states of haemoglobin?
Low affinity T state - difficult for oxygen to bind
High affinity R state - easier for oxygen to bind
How does O2 binding change the state of haemoglobin?
When pO2 is low haemoglobin is in T state so its hard for first oxygen molecule to bind
as each molecule binds it becomes more relaxed so each molecule gets easier to bind
What is the shale of a saturation haemoglobin curve?
Sigmoidal curve
What kPa is haemoglobin saturated above?
9-10 kPa
What kPa is haemoglobin half saturated at?
3.5 - 4
If haemoglobin concentration in the blood is 2.2 mmol/L, what should the oxygen content in the blood be?
8.8 mmol/L
What will happen to the concentration of oxygen in the blood if patient is anaemic?
If lungs are functioning ok the pO2 will be normal but the oxygen content will be lower as less bound to haemoglobin as less haemoglobin to bind to
What is tissue pO2 dependant on?
How metabolically active the tissue is
What is the typical pO2 in the tissues?
5 kPa
Can oxygen be removed from venous blood?
Mixed venous blood has been returned from various tissues
Over half oxygen content is still bound
The lower the tissue pO2 the more oxygen will dissociate
Some tissues may be able to remove some oxygen from the venous blood
How low can tissue pO2 get?
Cant fall below 3 kPa in most tissues as it must remain high enough to drive oxygen diffusion into cells
When can oxygen of tissues fall the lowest?
When there is a higher capillary density e.g. Heart muscle as it doesn’t have as far to diffuse
Describe the Bohr shift effect?
pH effects affinity of haemoglobin
In acidic conditions the curve shifts to the right and promotes T state in haemoglobin
Alkaline conditions promotes R state
The pH is lower in the most metabolically active tissues so extra oxygen is given up
How does temperature affect the oxygen dissociation curve?
Increased temperature shifts curve to the right
Metabolically active tissues have a slightly higher temperature so extra oxygen will be given up
How does 2,3-diphosphoglycerate (2,3-BPG) affect the dissociation curves?
Contained by normal red blood cells but in anaemia or at altitude the levels increase
This causes the curve to shift to the right which allows more oxygen to be given up to the tissues
When might 2,3-BPG levels drop?
In store blood due to refrigeration but this is not usually a problem clinically
Describe carbon monoxide poisoning?
Carbon monoxide reacts with haemoglobin to form COHb
Increases affinity of unaffected subunits for oxygen so they won’t give up at tissues
When is carbon monoxide poisoning fatal?
When HbCO > 50%
What is cyanosis?
Bluish colouration due to unsaturated haemoglobin
Deoxygenated haemoglobin is less red than oxygenated
Can be peripheral due to poor circulation or central due to poorly saturated blood in systemic circulation
What is pulse oximetry used for?
To detect level of haemoglobin saturation in pulsatile arterial blood
Doesn’t say how much haemoglobin is in blood though
What can give a better indication of how much haemoglobin is in blood?
An arterial blood gas and electrolyte analysis
