Haemoglobin And Gas Transport Flashcards
Roughly how much O2 is dissolved per litre plasma?
3mL
Describe the difference between arterial partial pressure of O2 and arterial O2 content
Arterial O2 partial pressure - the gaseous phase that is driving O2 into solution
Arterial O2 content - refers to O2 in solution and is determined by O2 solubility
What percentage of arterial O2 is extracted by peripheral tissues at rest?
25%
What percentage of oxygen is bound to haemoglobin in each litre of systemic arterial blood?
98%, the rest is dissolved in plasma
Describe how O2 binds to haemoglobin
Co-operatively to 4 molecules of oxygen.
1.34ml O2 binds to each gram of haemoglobin.
Describe the difference between arterial partial pressure of O2 and arterial O2 content
Arterial partial pressure - the O2 in solution, determined by O2 solubility
Partial pressure of O2 - in the gaseous phase that is driving O2 into solution
Describe how the demand of 250ml/min of O2 from resting tissues is met
150g/l of haemoglobin binds 1.34ml of O2 per g, so with a cardiac output of 5L/min the O2 delivery to tissues would be 1000ml/min
Describe the HbA form of haemoglobin
Makes up 92% of haemoglobin in RBC
Describe the HbA2 form of haemoglobin
Delta chains replace beta chains
Describe the HbF form of haemoglobin
Gamma chains replace beta chains
Describe the glycosylated Hb form of haemoglobin
Glucose molecules are added on to the haemoglobin. Useful in the diagnosis of diabetes and how its being controlled
State the haemoglobin saturation at the normal systemic arterial PO2 of 100mmHg
100%
State the haemoglobin saturation at PO2 60mmHg
90%
Describe the saturation of foetal haemoglobin in relation to normal haemoglobin at any given partial pressure of oxygen
HbF (foetal haemoglobin) has a higher affinity for O2 than HbA to extract O2 from maternal blood, therefore is more saturated at any given Kpa
Describe the saturation of myoglobin in relation to normal haemoglobin at any given partial pressure of oxygen
Myoglobin has a higher affinity for O2 than HbA to extract O2 from arterial blood, is therefore more saturated at any given Kpa
Describe anaemia
Any condition where the oxygen carrying capacity of the blood is compromised
State examples of when anaemia may occur
- iron deficiency
- Haemorrhage
- vitamin B12 deficiency (involved in production of red blood cells)
Describe the affect of anaemia on PaO2
Normal, as gas exchange will still occur normally, however not enough oxygen is being exchanged to maintain total blood O2 conc. ie there is a problem with the blood cells not diffusion at the lungs
State the affect on RBC O2 saturation in anaemia
RBC would still be fully saturated with O2, the number of binding sites isn’t affected, only the amount of oxygen available to bind.
An anaemic patient has an arterial oxygen content of 100m/l, what would be their % O2 saturation? Why?
Saturation ~100%, they have fewer cells/binding sites available but those that are available have oxygen bound.
Describe the effect of increased/decreased pH on the affinity of haemoglobin for O2
Acidosis (decreased pH) decreases affinity of haemoglobin for O2 so decreases saturation
Alkalosis (increased pH eg increased CO2) increases affinity of haemoglobin got O2 so increases saturation
Describe the effect of changes in PCO2 on % haemoglobin saturation
Decrease in PCO2 (20mmHg) increases the haemoglobin saturation
Increase in PCO2 (80mmHg) decreases the haemoglobin saturation
Describe the effect of changes in temperature on haemoglobin saturation
Decrease in temperature causes an increase in haemoglobin saturation
Increase in temperature causes a decrease in haemoglobin saturation
Describe the effect of addition/removal of 2,3-DPG
No 2,3-DPG causes an increase in haemoglobin saturation
Added 2,3-DPG causes a decrease in haemoglobin saturation
What is 2,3-DPG
2,3-diphosphglycerate which is synthesis by erythrocytes.
Increases in situations associated with inadequate O2 supply.
Helps maintain O2 supply in tissues
What is formed when carbon monoxide binds to haemoglobin?
Carboxyhaemoglobin, affinity is 250 times greater than O2
State the symptoms expressed when CO binds to haemoglobin
- hypoxia and anaemia
- nausea and headaches
- cherry red skin
- respiration rate unaffected due to normal arterial PCO2
- potential brain damage and death
State the treatment for CO poisoning
Provide 100% O2 to increase PaO2
Define hypoxia
Inadequate supply of oxygen to tissues
State the 5 main types of hypoxia
- hypoxia hypoxia
- anaemic hypoxia
- ischaemic hypoxia
- histotoxic hypoxia
- metabolic hypoxia
Describe hypoxia hypoxia
Reduction in O2 diffusion at lungs either due to decreased PO2 or tissue pathology
Describe anaemic hypoxia
Reduction in O2 carrying capacity of blood due to anaemia (RBC loss/iron deficiency)
Describe ischaemic hypoxia
When heart disease results in inefficient pumping of blood to lungs/around the body
Describe histotoxic hypoxia
When poisoning prevents cells utilising oxygen delivered to them eg in CO/cyanide poisoning
Describe metabolic hypoxia
When O2 delivery to the tissues foes not meet increased O2 demand by cells
Describe the ways in which CO2 is transported
- 7% remains dissolved in plasma and erythrocytes
- 23% combines in the erythrocytes with deoxyhaemoglobin to for carbamino compounds
- 70% combines in the erythrocytes with water to forms bicarbonate
Describe ‘chloride shift’
When CO2 combines with water to form bicarbonate, it moves out of the erythrocytes and into the plasma in exchange for Cl- ions and excess H+ ions bind to deoxyhaemoglobin.
Then carried to lungs in venous blood and reversed to allow dissolved CO2 to move into alveoli to be expired.
Describe how respiratory acidosis is brought about
Through Hypoventilation which causes CO2 retention. The equilibrium of CO2-> HCO3- is shifted to the right causing more H+ ions to be produced and the pH to decrease
Describe how respiratory alkalosis is brought about
Through hyperventilation, which allows more CO2 to be blown off. The equilibrium of CO2->HCO3- is shifted to the left which causes the H+ concentration to decrease which increases the pH
State the PO2 in arterial blood
100mmHg
State the PO2 in venous blood
40mmHg
State the PCO2 in arterial blood
40mmHg
State the PCO2 in venous blood
46mmHg
State the PO2 in resting cells
40 mmHg
State the PCO2 in resting cells
46mmHg
State PO2 in the alveoli
100mmHg
State the PCO2 in the alveoli
40mmHg
