Haemoglobin and gas transport Flashcards
How much oxygen is dissolved per litre of plasma?
3ml
Haemoglobin in red blood cells increases the oxygen carrying capacity to what?
200 ml/L
How is the bulk of CO2 transported?
In solution in plasma
Arterial partial pressure of oxygen is determined by what?
The oxygen dissolved in the blood (not haemoglobin)
What 2 factors influence how much O2 is dissolved, thus determining arterial partial pressure?
O2 solubility
The partial pressure of oxygen in the gaseous phase driving the O2 into solution (partial pressure in the alveoli)
What is the partial pressure of the oxygen in solution?
100mmHg, called the oxygen tension
Partial pressure of a gas in solution is equal to…
The partial pressure in the gaseous phase that is driving that gas into a solution
Gases travel in solution in the plasma rather than in a gaseous phase, why?
Gas in blood means bubbles in blood leading to a fatal air embolism
Oxygen delivery to the tissues can be calculated using what equation?
Arterial O2 content (ml/L) x Cardiac output (L/min)
O2 demand of resting tissues is…
250ml/min
What is the cardiac output?
5 L/min
How much haemoglobin is in the body?
150g/L
How much oxygen is carried in a gram of haemoglobin?
1.34ml O2 per g
What percentage of arterial oxygen is extracted by peripheral tissues at rest?
Only 25%
How is the PO2 gradient maintained between the blood and alveoli?
Haemoglobin takes up arterial oxygen so the gradient doesnt reach equilibrium
What percentage of haemoglobin is in the form HbA?
92%
What percentage of haemoglobin is in the form HbA2?
8%
What is the difference between HbA and HbA2?
Delta chains replace the beta chains
Haemoglobin in the form HbF (foetal) is formed when beta chains are replaced by what chains?
Gamma chains
What is HbA made of?
2 alpha and 2 beta chains
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 a much higher affinity for O2 than HbA.
How do muscles extract O2 from the blood?
BY having a higher O2 afinity than HbA
Oxygen is moved out of the alveoli down a partial pressure gradient until what?
The haemoglobin becomes saturated with oxygen
How long is haemoglobin in contact with the alveoli?
0.75s
Within how many seconds of contact with the alveoli is saturation complete?
Only 0.25s out of the 0.75
What is the major determinant of the degree to which haemoglobin is saturated with oxygen?
Partial pressure of oxygen in arterial blood
Oxygen is moved out of the alveoli down a partial pressure gradient until what?
The haemoglobin becomes saturated with oxygen
What is the normal systemic arterial PO2 and what level of saturation is heamoglobin at during this level?
100mmHg - Haemoglobin is almost 100% saturated at this level
What is the haemoglobin saturation when PO2 is 60mmHg? What does this allow for?
Still a high 90% which allows for a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced
At normal venous PO2, what is the reserve capacity?
75%
What do the higher affinities of myoglobin and foetal haemoglobin (compared to HbA) allow them to do?
Extract more oxygen from skeletal muscle for myoglobin
Foetal Haemoglobin - extract more oxygen from from the maternal blood
Define anaemia
Anaemia is defined as any condition where the oxygen carrying capacity of the blood is compromised
Can red blood cells to be fully saturated with oxygen in anaemia?
Yes
Why is it possible for red blood cells to be fully saturated with oxygen in anaemia?
As PaO2 is normal - there is no problem with ventilation or diffusion so alveolar volume and diffusion should be normal (exception is iron deficiency anaemia)
Is it possible to have low PaO2, and normal total blood O2 content?
No
Why is there a low oxygen content in anaemia?
Due to a low haemoglobin content as red blood cells are missing/not being synthesised properly due to anaemia
Why is iron deficiency anemia different?
As the number of O2 binding sites will be reduced BUT but those present will still be saturated if PaO2 is normal
What decreases the affinity of haemoglobin for oxygen
Decreased pH
Increased PCO2
Increased temperature Increased binding of DPG
In what state do these conditions have to be?
They have to exist locally in actively metabolising tissues
What is a positive and negative aspect to increased haemoglobin affinity for O2?
It aids the collection of oxygen in the pulmonary circulation but makes O2 offloading more difficult
What is DPG
2,3-diphosphoglycerate
What is DPG synthesized by?
The erythrocytes (red blood cells)
When would DPG levels be increased and how does it help?
In situations associated with inadequate oxygen supply (heart or lung disease, living at high altitude) and helps maintain oxygen release in the tissues.
How is carbon monoxide formed?
Incomplete combustion of carbon
Carbon monoxide binds to haemoglobin to form what?
Carboxyhaemoglobin
How much greater an affinity does haemoglobin have for CO over O2?
250x
Why is haemoglobins affinity for CO being so high a problem?
Because it will bind readily and dissociate very slowly making it hard to remove
Also only a small amount of CO - PCO of only 0.4mmHg causes progressive carboxyhaemoglobin formation
Typical PHYSICAL symptoms of carbon monoxide poisoning?
Cherry red skin, mucous membranes and nail beds
Headaches
Other sympotms of CO poisoning?
Aneamia and hypoxia
Why is repiration rate unchanged during CO poisoning?
As the arterial PCO2 levels remain unchanged and the main thing that drives ventilation is removing CO2
Eventual outcomes of CO poisoning?
Brain damage
Death
The treatment for CO poisoning is administering 100% oxygen, why is this treatment difficult?
Haemoglobin is already 98% saturated with oxygen, so providing pure oxygen can only increase this by 2%
5 main types of hypoxia?
Hypoxic Anaemic Ischaemic Histoxic Metabolic
What is the most common hypoxia?
Hypoxic
Describe Hypoxic hypoxia
Reduction in O2 diffusion at lungs either due to decreased PO2atmos or tissue pathology
What is anaemic hypoxia?
Reduction in O2 carrying capacity of blood due to anaemia (red blood cell loss/iron deficiency).
What is ischaemic (stagnant) hypoxia?
Heart disease results in inefficient pumping of blood to lungs/around the body
What is histotoxic hypoxia?
Poisoning prevents cells utilising oxygen delivered to them e.g. carbon monoxide/cyanide
What is metabolic hypoxia?
oxygen delivery to the tissues does not meet increased oxygen demand by cells.
What is hypoxia then?
A deficiency/inadequacy in the volume of oxygen reaching the tissues
When CO2 molecules diffuse from tissue to the blood, what percentage remains dissolved in plasma and erythrocytes?
7%
What does 23% of the CO2 do when diffusing from tissue to blood?
Combines in the erythrocytes with deoxyhemoglobin to form carbamino compounds
What does the remaining 70% do?
Combines in the erythrocytes with water to form carbonic acid
What does the carbonic acid go on to form?
Bicarbonate and H+ ions
What does this bicarbonate and H+ ions go on to do?
Bicarbonate moves out of the erythrocytes into the plasma in exchange for Cl- ions (chloride shift)
Excess H+ ions bind to deoxyhemoglobin
What equation shows why CO2 can change the ECF’s pH?
CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
Why is pH normally stable?
Because the all CO2 produced is eliminated in expired air
CO2 retention leading to increased [H]+ will cause what?
Respiratory acidosis
Blowing off more CO2 leading to decreased [H]+ will cause what?
Respiratory alkalosis
Is respiratory alkalosis found in hypo or hyper-ventilation?
Hyperventilation
Is respiratory acidosis found in hypo or hyper-ventilation?
Hypoventilaton
