6 Haemoglobin & Gas transport Flashcards
How much Oxygen is dissolved in every litre of plasma?
3ml/L
What is the oxygen carrying capacity of the blood?
200 ml/L
What determines the arterial partial pressure of O2?
Oxygen dissolved in the blood
NOT the oxygen carried by haemoglobin
What 2 factors influence how much O2 is dissolved?
- Its solubility
- The partial pressure of gaseous oxygen driving O2 into solution (partial pressure in alveoli)
What is the partial pressure of the oxygen in solution?
100mmHg (oxygen tension)
Equal to PO2 driving it across
What is the oxygen demand of resting cells?
250ml/min
What is cardiac output?
Around 5L/min
How much haemoglobin is in the average person?
150g/L
How much oxygen is carried in every gram of haemoglobin?
1.34ml of O2 per gram of haemoglobin
How much oxygen is carried in the haemoglobin of a normal person?
[150g haemoglobin/L]
[5L/min cardiac output]
[1.34ml O2/g of haemoglobin]
5 litres every minute
-> 5L x 150g = 750g/min
1.34ml O2/g
-> 750 x 1.34 = 1000ml/min
How much of the arterial O2 is extracted by tissue at rest?
Only 25%
Resting tissues use 250ml/min and haemoglobin carries 1000ml/min
How is the PO2 gradient maintained between the blood & alveoli?
Haemoglobin takes up arterial oxygen so the gradient doesnt reach equilibrium
What is the most common form of Haemoglobin?
HbA
Makes up 92% of haemoglobin
Made of 2 alpha & 2 beta chains
What are some other types of haemoglobin?
HbA2
HbF (Foetal)
Glycosylated Hb
myoglobin
What makes up foetal haemoglobin?
2 Alpha chains
2 Gamma chains
What makes up HbA2?
2 Alpha chains
2 Delta chains
What are the types of glycosylated Hb?
HbA1a
HbA1b
HbA1c
Where is myoglobin found?
Oxidative muscle fibres
How does a foetus extract O2 from maternal blood?
HbF has higher affinity for O2 than HbA.
How do muscles extract O2 from the blood?
Myoglobin has higher O2 affinity than HbA
How long is haemoglobin in contact with the alveoli?
Around 0.75 seconds
Only takes 0.25s to become saturated
How far can PAO2 drop before haem saturation goes below 90%?
PAO2 can be 60mmHg without losing much arterial oxygen
What factors can affect the affinty of haemoglobin for Oxygen?
- pH
- PaCO2
- Temperature
- Diphosphoglycerate
What kind of people produce more diphosphoglycerate?
People who live at high altitude
Those with heart or lung disease
What is the main determinant of haemoglobin saturation?
The PaO2
See graphs for how saturation is affected by various factors
What decreases haemoglobin’s affinity for oxygen?
- pH drop
- PaCO2 increase
- Temp rise
What is the physiological benefit of decreasing haemoglobin’s affinity for oxygen?
Low pH, high PaCO2 & high temp exist in actively metabolising tissues and decrease haemoglobin’s affinity for oxygen.
This facilitates dissociation of oxygen from haemoglobin.
What increases haemoglobin’s affinity for oxygen?
- pH rise
- PCO2 fall
- Temp fall
Whats the effect of increased haemoglobin affinity for oxygen?
Oxygen unloading is more difficult at tissues
Easier to collect oxygen in pulmonary circulation
What does 2,3-DPG do?
Decreases haemoglobin’s affinity for oxygen
What makes 2.3-DPG?
Erythrocytes
Why is 2,3-DPG made in situations with inadequate oxygen?
Helps maintain oxygen release at tissues.
Define anaemia?
Any condition where O2 carrying capacity of blood is compromised
Give some examples of Anaemic conditions?
- Fe deficiency, cant make enough haem
- Haemorrhage, losing blood
- Vit B12 deficiency
Why is PaO2 normal in anaemia?
No problem with ventilation or gas exchange
No reduction in amount dissolved in blood
How does anaemia affect the saturation of haemoglobin?
RBCs would still be fully saturated its just theres less of them
What do CO & haemoglobin form?
Carboxyhaemoglobin
Describe the affinity of CO for Haemoglobin?
CO has affinity 250x greater than O2 for haemoglobin, prevents transport of oxygen
What partial pressure of CO causes carboxyhaemoglobin formation?
0.4mmHg PaCO needed to cause progressive carboxyhaemoglobin formation
What are the symptoms of CO poisoning?
- Hypoxia & Anaemia
- Nausea & Headaches
- Cherry red skin & Mucous membranes
- Potential brain damage & death
What is the main thing that drives ventilation?
Getting rid of CO2
How many types of hypoxia are there?
5
Define hypoxia?
An inadequate supply of oxygen to tissues
What is the most common form of hypoxia?
Hypoxic Hypoxia
- Tissue pathology
- Decreased atmospheric PO2
- Reduced O2 diffusion at lungs
What is the cause of anaemic hypoxia?
Anaemia leads to reduced O2 carrying capacity
What is the cause of Ischaemic (stagnant) hypoxia?
Heart Pathology
-> Inefficient blood pumping
How does histotoxic Hypoxia occur?
Tissue Poisoning (e.g. Hydrogen sulphide or cyanide)
-> Cells cant use oxygen thats delivered to them
What causes metabolic hypoxia?
Tissue Oxygen demand increases
-> Oxygen delivery to tissues doesn’t meet new demands
How is CO2 transported in the blood?
- 70% as carbonate in solution
- 7% in solution alone
- 23% in RBCs as carbamino compounds (Formed with deoxyhaemoglobin)
Whats the equation for how CO2 affects ECF pH?
CO2 + H2O ↔ H2CO3 ↔ HCO3 + H+
What is carbonate/carbonic acid?
Carbonic acid = H2CO3
Carbonate = HCO3
Why does plasma pH alter during hypo/hyperventilation?
They alter PaCO2, moving the equation and altering [H+]
How does hypoventilation affect plasma pH?
Hypoventilation
-> CO2 retention
-> [H+] increases
-> Respiratory acidosis
How does hyperventilation affect plasma pH?
Hyperventilation
-> Blowing off more CO2 than normal
-> [H+] decreases
-> Respiratory Alkalosis
