Ventilation and Diffusion Flashcards
How do you convert from mmHg to kPa?
mmHg x 0.133322
What is atmopheric pressure at sea level?
760mmHg
101.325kPa
What are the partial pressure of nitrogen, oxygen and carbon dioxide at normal atmopshier pressure?
Nitrogen = 593mmHg
Oxygen = 159mmHg
Carbon Dioxide = 0.29mmHg
What happens to partial pressure if atmopsheric pressure changes?
partial pressure changes?
Oxygen can be toxic at high levels. What can be used to replaced it?
trimix - nitrogen-oxygen-helium
Heliox - oxygen-helium
What is dalton’s law of partial pressure?
in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
What is Henry’s Law?
when a mixture of gases is in contact with a lquid, each gas will dissolve in the liquid in proportion to its partial pressure
partial pressure = 10kPa vs 1kPa
x10 more gas will go into solution if its partial pressure is 10kPa compared to 1kPa
What occurs if the partial pressure in the liquid becomes greater than in the air?
gas will move out of the liquid
What does the abolsute level of gas dissolved in liquid also depend on?
solubility of the gas
Rate the gases in order of solubility at atmopsheric pressure
CO2 = most soluble
O2 = 1/20th as soluble
N2 = barely soluble
What occurs if a gas enters a chemical reaction?
the total amount of gas in the liquid is the amount of gas dissolved plus that chemically bound in solution
What is alveolar gas not?
atmopsheric air
How do the conudtcing passages of the respiratory system alter atmopsheric air?
humidify the air so it is warm and moistened
What is the water vapour pressure of warm and moistened air?
47mmHg
What is the partial pressure of alveolar gas?
760-47 = 713mmHg
What is the partial pressure of O2 and CO2 in the lungs and give an explanation for these values
- O2 = 104mmHg
- CO2 = 40mmHg
- alveolar air is made up of fresh air plus the air that remained in the lungs after the last breath
What must happen for gas exchange to occur between the alveolar air and the blood?
- dissolve in the aqueous layer (surfactant lining the alveoli)
- diffuse across the capillary membrane
- enter the blood
What are the major factors that affect the rate of diffusion?
- proportional to surface area, solubility, concentration gradient (difference in partial pressure)
- inversly proprtional to tissue thickness, √molecular mass
What is the main impact of the rate of diffusion
limitis how much air gets into the blood
How are the lungs adapted to maximase gas exchange?
- surface area is large
- large number of alveoli
- small thickness
- concentration gradient is large
- molecular mass between gases is insignficiant
- CO2 is much more soluble than O2
Draw a diagram showing the change in PO2 from the start of the capillary to the end
Why does CO2 need a smaller concentration gradient into flow into and out of the blood compared to O2
More soluble than O2
How does oedema alter the respiratory membrane?
thickness increases
Full transmit time may not be sufficient enough to complete full gas exchange
More marked effect on O2 than CO2 due to difference in solubility
In what condition is the surface area of the lungs decreased and how does this affect gas exchange?
Empheysema
gas exchange is reduced
