5 Properties of Gases and Gas exchange in the Lung Flashcards
What is Dalton’s law?
In mixture of gases- each component exerts partial pressure
What unit do we use to measure pressure in medicine?
kPa
What % oxygen does air contain?
21%
If the partial pressure of oxygen in alveolar air is 13.3% and the air is allowed to equilibrate with the blood in the pulmonary capillaries, what will be the partial pressure of oxygen in the blood leaving the alveolus?
(Atmospheric pressure= 101.1 kPa)
Partial pressure of oxygen in the blood leaving the alveolus: 13kPa
Partial pressure of a gas and content of dissolved gas in a liquid are not the same. Henry’s law shows the relationship between them. What is Henry’s law?
Dissolved gas in liquid (mmol/L) = partial pressure of gas (kPa) x solubility coefficient of gas
What is the solubility coefficient?
Amount of gas that will dissolve in 1L of plasma at 37 degrees C, when exposed to given partial pressure
How does the solubility coefficent of CO2 differ from that of O2?
Solubility coefficent of CO2 > Solubility coefficent of O2
What is the standard vapour pressure of water vapour at body temperature (37 degrees C) ?
6.28 kPa
Where does inhaled air become saturated with water vapour?
Upper respiratory tract.
The normal value of partial pressue of oxygen in the alveolar gas is about 13.3 kPa. Since atmospheric partial pressure of oxygen is about 21 kPa, explain the difference.
- Inhaled air saturated with water vapour- partial pressure of O2 = 19.8 kPa
- In alveoli- O2 taken up by blood- so partial pressure lower
What is the normal value for the partial pressure of CO2 in the alveolar gas?
5.3kPa
What is meant by ‘mixed venous blood’?
Blood from superior vena cava, inferior vena cava and coronary sinus
(ie deoxgenated venous blood from body)
What are the partial pressures of oxygen and carbon dioxide in the mixed venous blood reaching the capillaries?
pO2= 6kPa
pCO2= 6kPa
Name the 3 factors which determine the the rate of gas exchange in the alveoli.
- Area available for exchange
- Resistance to diffusion
- Gradient of partial pressure
There are 5 key structures which the gas must diffuse through from entering the alveoli to entering a red blood cell. What are these structures?
What is the thickness of this barrier overall?
- Alveolar epithelia cell
- Interstitial fluid
- Capillary endothelilal cell
- Plasma
- Red cell membrane
Thickness: 0.6 micron