Principles of gas exchange Flashcards
What are the three layers that make up the alveolar wall?
1) alveolar epithelium
2) Basement membrane
3) capillary endothelium
What is the rate of diffusion of gases proportional to?
A X ΔP (Surface area X pressure gradient)
What is the pressure gradient?
Difference in partial pressures of the respective gases in the alveolus and the blood
What is the partial pressure of a gas?
Pressure that the gas would exert if it was the only gas in the container
What is the universal gas equation?
PV = nRT (Pressure in atmosphere X volume in litres = no of particles in moles X the ideal gas constant X temp in kelvin)
What is dalton’s law?
The partial pressure of a gas in a mixture = Total pressure X fractional concentration of the gas
What is the percentage of oxygen in the atmosphere?
21%
What is the percentage of nitrogen?
79%
Why is the partial pressure of oxygen in the alveoli lower than in room air?
Partial pressure is lower in the alveoli because, inspired air is humidified in the upper airway (saturated with water vapour). HUMIDIFICATION DECREASES P02 in upper airway.
What is the typical value if alveolar partial pressure of CO2?
5 kPA
What is Henry’s law?
In equilibrium - the partial pressure of the gas in a solution if the same as the partial pressure of the gas above the solution
What is the relationship between partial pressure of gas and solubility?
Solubility is inversely proportional to the partial pressure of a gas in solution. So high solubility means low partial pressure of gas. This is because if a gas is really soluble, then it would not want to escape the solution, it will rather remain, so the partial pressure the gas exerts in the solution will be low. vice versa
What is the alveolar partial pressure of oxygen?
13.7 kPA
What is the oxygen diffusing capacity?
= O2 uptake / (alveolar pO2 - mean pulmonary capillary pO2)
What is the carbon monoxide diffusing capacity?
= carbon monoxide uptake / alveolar PCO
