Lecture 5- Gas exchange Flashcards
Boyles law
- Pressure (P) of a gas is inversely proportional to its volume (V)
- (if temperature & number of gas molecules remains constant in a closed system)
- This means that if you expand the space in which a gas is contained – the pressure will drop.
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Kinetic theory of gases
Gas pressure is caused by the collisions of gas particles with the walls of the container
partial pressure gases
def: pp of gas is the pressure exerted by an individual gas in a mixture of gases
- Describes amount of a specific gas within a gas mixture
- Uses gas pp gradient to explain gas diffusion
- Gases diffuse down their pp gradient from high to low pp
- Use pp to calculate amount of gas dissolved in liquid
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Calculating pp of gas in a gas mixture
(% gas A)x (total pressure) = partial pressure gas A
- Assumes there are no chemical reactions between gases
- Application of Daltons law
- In a. Mix of non-reacting gases, total pressure exerted is equal to the sum of pp of the individual gases
atmospheric pressure is the
- pressure exerted by the weight of the air above the earth in the atmosphere
At high altitudes
atmospheric pressure is lower (weight of air pressing down is less)
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percentage of oxygen in atmospheric air
20.9%
percentage of nitrogen in atmospheric air
78%
percentage of argon in atmospheric air
0.17%
percentage of carbon dioxide in atmospheric air
0.03%
total atmospheric pressure (dry) at sea level
101kPa
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partial pressure of O2 at dry atmopheric pressure at sea level
pp O2= 20.9% of 101kPa
therefore
0.209 x 101 kpa= ppO2= 21.1kPa
When we breath in air it is
moistened, water molecules in vapour form are added to air
Water vapour exerts a pressure called
saturated vapour pressure
displaces a proportion of the total pressure of the mixture of gases- in this cases, total atmospheric pressure
Saturated vapour pressure =……….. at body temp- only depends on temp
6.28 kPa
We need to subtract …………………from the total pressure of the dry gas mixture to arrive at the total pressure of gas mixture in a moist environment
water vapour pressure
pp of O2 and nitrogen in air we breath in (moist) at atmospheric pressure
therefore 101(kPa) – 6.28 (kPa) = 94.7 kPa =total pressure of gas mixture in a moist environment
- The other gases are still in the same ratios as in dry air
- pO2 = 94.7 kPa x .209 = 19.8 kPa= partial pressure oxygen in URT
- pN2 =(101-6.28)x.79 =73.8kPa
pCO2
partial pressure CO2- generic
pO2
partial pressure O2- generic
PACO2
partial pressure CO2 in alveoli ( big A= alveoli)
PAO2
partial pressure O2 in alveoli (big A= alveoli)
PaCO2
pp CO2 in arterial blood (little a= arterial)
PaO2
pp O2 in arterial blood (little a= arterial)
PvCO2
pp CO2 in venous blood
PvO2
pp O2 in venous blood
pp O2 in upper repiratory tract is…….. kPa
but
alveolar pp O2 is….
- 8kPa
- 3 kPa