6/7. Haemoglobin and Gas Transport Flashcards
What is the role of blood in gas transport?
Transports O2 from lungs to tissues to use in energy production and transports the waste product of this process CO2 from tissues to lungs for removal.
How much O2 is dissolved per litre of plasma?
3ml
How is the carrying capacity of blood increased to 200ml/L?
Haemoglobin in red blood cells
How is CO2 carried?
In various forms, in solution in plasma
What is arterial partial pressure of O2 determined by?
O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution
What does arterial partial pressure of O2 refer to?
The O2 in solution
What are the values assigned to the partial pressure of a gas in solution equal to?
The partial pressure in gaseous phase that is driving that gas into solution
What is the solubility of O2 in water?
Low
0.03ml/L/mmHg
What is PaO2 sometimes referred to as?
Oxygen tension
What is the PO2 in solution equal to?
PO2 in the gaseous phase that results in that oxygen concentration in the liquid phase
Why is it important that gases do not travel in the gaseous phase in plasma?
If they did there would be bubbles in the blood which would result in a fatal air embolism
What is the oxygen demand of resting tissues?
250ml/min
What percentage of arterial O2 is extracted by peripheral tissues at rest?
25%
What is the O2 delivery to tissues?
15ml/min
What is the O2 delivery to tissues using haemoglobin?
1000ml/min
What does each litre of systemic arterial blood contain?
200ml of oxygen, of which more than 98% is bound to haemoglobin. The remaining oxygen is dissolved in plasma
What reaction takes place when oxygen cooperatively binds to haemoglobin?
Oxygenation
What volume of oxygen binds to each gram of haemoglobin?
1.34ml
What is the most abundant form of haemoglobin in RBC?
HbA (92%)
Apart from HbA what other forms of haemoglobin are found in RBC?
- HbA2 where the omega chains replace the beta
- HbF where gamma chains replace the beta
- Glycosylated Hb ( HbA1a, HbA1b, HbA1c)
What is the major determinant of the degree to which haemoglobin is saturated with oxygen in arterial blood?
Partial pressure of oxygen
How does Hb become saturated with oxygen?
Hb sequesters O2 from the plasma, maintaining a partial pressure gradient that continues to suck O2 out of the alveoli
How long does it take for saturation to be complete on contact with the alveoli?
0.25s
When is haemoglobin almost 100% saturated?
At the normal systemic arterial PO2 of 100mmHg
At PO2 of 60mmHg, haemoglobin is 90% saturated. What does this permit?
This permits a relatively normal uptake of oxygen by the blood even when the alveolar PO2 is moderately reduced
What is the reserve capacity at normal venous PO2?
75%
What has a higher affinity for O2 than haemoglobin?
- Myoglobin
- Foetal haemoglobin
Why does foetal haemoglobin have a higher affinity for oxygen than regular haemoglobin?
It is necessary for it extracting O2 from maternal/arterial blood
Anaemia
Any condition where the oxygen carrying capacity of the blood is compromised
Why does PaO2 remain normal in anaemia?
It has no effect on ventilation or diffusion
What are 3 causes of anaemia?
- Iron deficiency
- Haemorrhage
- Vitamin B12 deficiency
What does the affinity of haemoglobin for O2 change in response to?
Certain chemical factors
What are 4 factors which can change the affinity of haemoglobin for O2?
- pH
- PCO2
- Temperature
- DPG
What will shift the curve to the right?
- Lower pH
- Higher PCO2
- Higher temperature
- Additional DPG
What will shift the curve to the left?
- Higher pH
- Lower PCO2
- Lower temperature
- No DPG
When is there an increase in DPG?
In situations associated with inadequate oxygen supply such as heart/lung disease and living at altitude
What happens when CO binds to haemoglobin?
It forms carboxyhaemoglobin which binds readily to O2 and dissociates very slowly
How many times greater is the affinity of caarboxyhaemoglobin for oxygen than haemoglobin for oxygen?
250 time greater
What is the minimum PCO required to cause progressive carboxyhaemglobin formation?
0.4mmHg
What are the symptoms of CO poisoning?
- Hypoxia and anaemia
- Nausea and headaches
- Cherry red skin and mucous membranes
What can Co poisoning result in?
Potential brain damage and death
Why is the respiration rate unaffected with CO poisoning?
There is normal PCO2
Hypoxia
Inadequate supply of oxygen to tissues
What are the 5 main types of hypoxia?
- Hypoxic hypoxia
- Anaemic hypoxia
- Ischaemic hypoxia
- Histotoxic hypoxia
- Metabolic hypoxia
Hypoxic Hypoxia
Reduction in O2 diffusion at lungs either due to decreased PO2atoms or tissue pathology
Anaemic Hypoxia
Reduction in O2 carrying capacity of blood due to anaemia
Ischaemic Hypoxia
Heart disease results in inefficient pumping of blood to lungs/around the body
Histotoxic Hypoxia
Poisoning prevents cells utilising oxygen delivered to them
Metabolic Hypoxia
Oxygen delivery to the tissues does not meet increased oxygen demand by cells
What happens to CO2 molecules when they diffuse from the tissues into the blood?
- 7% remains dissolved in plasma and erythrocytes
- 23% combines in the erythrocytes with deoxyhaemogolbin to form carbamino compounds
- 70% combines in the erythrocytes with water to form carbonic acid which then dissociates to yield bicarbonate and H+ ions
What happens to most of the bicarbonate?
It moves out of the erythrocytes into the plasma in exchange for Cl ions and the excess H+ ions bind to deoxyhaemoglobin.
What happens in the pulmonary capillaries?
Co2 moves down its concentration gradient from blood to alveoli
Why is pH normally stable?
All CO2 produced is eliminated in expired air
What will alter plasma PCO2 and plasma [H+]?
Hypoventilation and hyperventiliation
What does hypoventilation lead to?
It causes CO2 retention which leads to increased {H+} bringing about respiratory acidosis
What does hyperventilation lead to?
Blowing off more CO2 leads to decreased [H+] bringing about respiratory alkalosis
