Lecture 4: Physical Principles Of Gas Exchange Flashcards
What is diffusion?
Random molecular motion of molecules
Movement of a gas in one direction is the effect of…
A concentration gradient
Direction of diffusion occurs from areas of ___ to ___
High to low concentration
Rate of diffusion is dependent on ___
Pressure
Total pressure of mixture =
The summation of partial pressures of gases in a mixture
Respiratory gases include (3)
- Oxygen
- Nitrogen
- Carbon dioxide
Composition of air
- 79% nitrogen
- 21% oxygen
Total pressure of air mixture =
760 mm Hg
1 atmosphere =
760 mm Hg
Nitrogen partial pressure
79% of 760 mm Hg = 600 mm Hg
Oxygen partial pressure
21% of 760 mm Hg = 160 mm Hg
Henry’s Law—Solubility of a gas in a liquid depends on what 4 things?
- Temperature
- Partial pressure of gas over the liquid
- Nature of the solvent
- Nature of the gas
When dissolved molecules are attracted by water more and can be accumulated without building up excess pressure in solution = ___ soluble
Highly soluble
Molecules which are repelled by water will dissolve less and have lower concentration = ___ soluble
Poorly soluble
Carbon dioxide is ___ times more soluble than oxygen
20 times
Rate of net diffusion of gases is determined by…
Difference of partial pressures (pp)
If pp of gas in alveoli > blood, then…
Gas moves into blood (i.e.: oxygen)
If pp of gas in blood > alveoli, then…
Gas moves into alveoli (i.e.: carbon dioxide)
What is vapor pressure?
Partial pressure of water escaping surface into gas phase
Vapor pressure is ___ mm Hg when gas mixture is fully humidified at 37 degrees Celsius
47 mm Hg
Vapor pressure depends on ___
Temperature
At greater temperature, the ___ the kinetic energy and ___ water escaping into the ___ phase
Greater the kinetic energy, more water escaping into the gas phase
How do you calculate the pp of O2 in the upper airway?
760 mm Hg (total) = 713 mm Hg (pp Air) + 47 mm Hg (pp H2O vapor)
Pp of O2 in upper airway = 713 mm Hg x 0.21 = 150 mm Hg
What are 6 factors that affect gas diffusion rates?
- Pressure differences
- Gas solubility in fluid
- Area of fluid
- Distance which gas must diffuse
- Molecular weight of gas
- Temperature of fluid (constant in body)