Haemoglobin and gas transport Flashcards
How many mL of O2 are dissolved per litre of plasma?
3ml
What is the effect of haemoglobin in terms of increasing the carrying capacity of O2 of RBCs?
Increases the carrying capacity of RBCs to 200ml/l
Explain PaO2 in terms of gas transport
PaO2 describes O2 in solution ONLY.
Does NOT describe arterial O2 content
PaO2 in the gaseous phase is what is driving the O2 into solution.
Therefore, the partial pressure of gas in a solution is = to the partial pressure driving gas into solution.
Define oxygen tension and state its value and how this is calculated
Oxygen tension: pressure driving O2 into solution = 100mmHg
O2 solubility = 0.03ml/L/mmHg and
3ml of O2 per L of plasma so
3/0.03=100mmHg
What is the O2 demand of resting tissues?
250ml/min
Compare how plasma alone would meet the O2 demand of resting tissues to when haemoglobin is present
Plasma: 3ml/L x a Cardiac output of 5L/min would equal 15ml/min of O2 delivered to tissues
Haemoglobin: 200ml/L x a CO of 5L/mon would equal 1000ml/min of )2 delivered to tissues, therefore only 25% of O2 acquired by haemoglobin is taken up by tissues
What is the volume of O2 in every litre of systemic arterial blood?
What proportions are bound to haemoglobin or dissolved in solution?
Volume of O2 in systemic arterial blood: 200ml/L
98% is bound to haemoglobin, the rest is dissolved in solution
How many oxygen molecules can co-operatively bind to one molecule of haemoglobin?
4
How many grams of haemoglobin are there per litre of plasma?
150g/l
How millilitres of oxygen are there per gram of haemoglobin?
1.34ml/g
What is the determinant of the degree of saturation of haemoglobin?
The partial pressure of oxygen in arterial blood
Describe the proportions of the different types of haemoglobin in blood
92% is HbA - 2alpha and 2beta chains
8% is HbA2 (2alpha and 2delta chains), HbF(2alpha and 2gamma chains) and glycosylated Hb (HbA1a, 1b and 1c)
How does haemoglobin help to maintain the partial pressure gradient of oxygen?
Hb sequesters O2 from plasma maintaining a partial pressure gradient that enable s oxygen to be sucked from the alveoli until the haemoglobin is saturated with oxygen. This is maintained by the partial pressure in the plasma as opposed to the partial pressure in the alveoli.
How long does it take for haemoglobin to become saturated?
Within 0.25s contact with alveoli
Total contact time = 0.75s
Describe the oxygen haemoglobin saturation curve
Nearly 100% (98%) saturated at 100mmHg (normal PaO2)
Permits normal O2 uptake even when PAO2 low e.g. 90% saturated at 60mmHg
Even at 40mmHg (the normal PvO2) there is a 75% reserve capacity
Where to myoglobin and foetal haemoglobin sit in comparison to haemoglobin on the oxygen haemoglobin concentration curve?
The myoglobin curve sits the most to the left. This is because it is concentrated in oxygen muscle fibres. More dependent on aerobic respiration. Higher affinity to O2 so it can be extracted from exercising muscle.
The foetal haemoglobin curve sits between the myoglobin cure and the haemoglobin curve. This is so oxygen can be extracted from maternal blood.
What happens to PaO2 at high altitudes and what does the body do to adjust to this?
PaO2 falls BUT total oxygen doesn’t fall as much as the partial pressure of oxygen in cells changes to maintain the gradient.
Define anaemia and give examples
When the oxygen carrying capacity of the blood is compromised
E.g. iron deficiency, B12 deficiency
Explain why PaO2 is normal in anaemia
PaO2 is normal because PAO2 is normal - there is no problem with diffusion. Therefore, you can have a normal PaO2 while the total oxygen low but you can’t have an abnormal PaO2 and a normal total blood content.
Why is SpO2 normal in anaemia?
Because although there is less haemoglobin present, the haemoglobin that is present will be saturated with oxygen. (Except in iron deficiency anaemia where there are less oxygen binding sites but the binding sites that are present are saturated).
Why would the oxygen-haemoglobin concentration curve shift to the left?
State the factors that would cause this.
To increase the affinity of haemoglobin for oxygen. There is therefore reduced unloading but increased This would be caused by - increased pH - reduced PCO2 - reduced temperature - no DPG
Why would the oxygen-haemoglobin concentration curve shift to the right?
State the factors that would cause this.
To reduce the affinity of haemoglobin for oxygen. This increased unloading locally in actively metabolising tissues. This would be caused by - reduced pH - increased CO2 - increased temperature - DPG
Describe DPG
2,3-DPG synthesised by erythrocytes
Associated with situations of inadequate oxygen supply (heart of lung disease, living at high altitude)
Helps oxygen be released in periphery tissues only.
Describe the effect of carbon monoxide
CO binds to haemoglobin -> carboxyhaemoglobin
Has affinity to haemoglobin 250x greater than oxygen
Dissociates very slowly
PaCO of only 0.4mmHg causes carboxyhaemoglobin formation
Why is respiratory rate normal in CO poisoning?
Respiratory rate is normal because arterial PCO2 is normal.
What are the symptoms of carbon monoxide poisoning?
Symptoms: hypoxia and anaemia, cherry red mucous membranes and skin
Define hypoxic hypoxia
Decreased O2 diffusion at lungs due to decreased atmospheric or tissue PO2
Define anaemic hypoxia
Decreased O2 carrying capacity due to anaemia (RBC loss or iron deficiency anaemia)
Define ischaemic/stagnant hypoxia
Heart disease causes insufficient pumping of blood to lungs/round the body
Define histotoxic hypoxia
Poison eg cyanide/CO prevents cells utilising O2 delivered
Define metabolic hypoxia
Oxygen delivered to tissues does not meet the oxygen demand by cells
Describe the proportions of CO2 transport in the blood
7% dissolved in plasma
23% combined w/ deoxyhaemoglobin in erythrocytes forming carbaminocompounds
70% combines with water in erythrocytes and is then held as HCO3^(-) in plasma
Describe how combines with water in erythrocytes and is then held as HCO3- in plasma
Carbon dioxide dissolves in water CO2 + H20 -> H2CO3^(2-)
H2CO3^(2-) dissociates to hydrogen ions (H^+) and bicarbonate ions (HCO3(-))
The H+ ions combine with haemoglobin while the bicarbonate moves into the plasma in exchange for chloride ions.
Reverse occurs at alveoli
