Carriage of Gases Flashcards
What is the equation for pressure?
Pressure = Force/Area
What units can be used for pressure?
- kPa (kiloPascal)
- N/m²
- mmHg (millimetres of mercury)
What is partial pressure?
- In a mixture of gases, each one exerts an individual pressure- partial pressure
- Partial pressure of any gas is independent of other gases in a mixture
- If other gases were removed, the partial pressure would equal total pressure
What is Dalton’s law?
- Total pressure is equivalent to sum of component partial pressures
- E.g. Atmospheric pressure is 100kPa and oxygen constitutes 21% of air, there oxygen partial pressure = 21kPa
- In lower altitude oxygen partial pressure is also lower
What is the relationship between partial pressure and solubility?
- Gases dissolve in aqueous solutions
- At equilibrium, partial pressure of a gas in solution is equal to that of gaseous form
What is Henry’s Law?
[Gas]= partial pressure x solubility coefficient
- Each gas has its own solubility coefficient
- Also dependent on factors like temperature
How is oxygen carried in the blood?
- Dissolved in plasma
- Bound to haemoglobin (found in erythrocytes)
What is the normal range of haemoglobin in females?
- 11.5-16.0g/100 ml
What is the normal range of haemoglobin in males?
- 13.5-18.0g/100ml
What is the importance of haemoglobin?
- Haemoglobin is important because otherwise we would need a large cardiac output
- 99% of oxygen carriage comes from haemoglobin
How does oxygen enter the blood from the lungs?
- Diffusion from alveoli to the blood
- High pressure to low pressure
How is oxygen delivered to tissue?
- Oxygen travels from blood into interstitium
- From interstitial into cells
- From cells into mitochondria for oxidative phosphorylation
- Partial pressure from blood to mitochondria is decreasing so oxygen moves down a gradient
Describe the structure of haemoglobin
- 4 sub- units each with global chain (peptide) and haem group (porphyrin ring)
- Each subunit will bind to 1 molecule of oxygen
- Saturated haemoglobin therefore will bind to 4 oxygen molecules
How much oxygen does 1g of haemoglobin bind to?
- 1.36ml of oxygen at body temperature and pressure
- Hb is then saturated
What is anaemia?
- Anaemia is the lack of Hb in the blood
- Less haemoglobin means less total oxygen content regardless of saturation
What does anaemia result from?
- Impaired production (iron deficiency etc.)
- Increased breakdown (haemolysis)
- Blood loss (haemorrhage)
- Fluid overload (haemodilution)
Describe the structure of adult haemoglobin (HbA)
- 2 alpha chains of 141 amino acids
- 2 beta chains of 146 amino acids
What percentage of adult haemoglobin in HbA₂?
2%
Describe the structure of HbA₂
- 2 alpha chains
- 2 delta chains replace the beta chains
What percentage of adult Hb is HbF (foetal haemoglobin)?
1%
Describe the structure of foetal haemoglobin
- 2 alpha chains
- 2 gamma chains replace beta chains
What is foetal haemoglobin?
- Embryonic forms replaced by HbF from 13 weeks of gestation
- At birth, majority of Hb is still HbF (80%)
- Switched to adult forms occurs between 3-6 months of age
- HbF not fully replaced and is approximately 1% adult Hb
What are some genetic defects that can occur in globin chains?
- Commonest of all genetic disorders
- Thalassaemia- defect in synthesis of globin chains
- Sickle cell disease- defect in structure of globin chains
What is Thalassaemia?
- Inherited defects in globin chain synthesis
- Can either be alpha or beta thalassaemia depending on chain affected, Hb not made properly
- Leads to imbalance of chains result in decreased erythropoiesis and increased haemolysis of mature cells