Quiz 4 Physical Principles of Gas Exchange Flashcards
What is the mechanism and rate of molecule transfer dependent on ?
- Physics of gas diffusion
- Partial pressures of gases involved
What is the energy source for gas diffusion?
Kinetic motion
Molecular movement is ______ and ______
Continual and random
Movement of a gas in one direction is the effect of what?
Concentration gradient
Direction of diffusion occurs for areas of ______ to _______ concentration.
High to low
Simple diffusion
Rate of diffusion is dependent on what?
Pressure
What is partial pressure?
The pressure a gas would exert by it’s self.
What is the total pressure of a mixture?
The summation of all the partial pressures in a gas
True or False: Each gas exerts its own individual pressure on the respiratory wall surface?
True
What is the mixture of air?
Nitrogen 79%
Oxygen 21%**
What is the total pressure of the air mixture?
760 mm Hg*
What does 1 atmosphere equal?
760 mm Hg*
What is the partial pressure of nitrogen in one atmosphere?
600 mm Hg
What is the partial pressure of oxygen in one atmosphere?
160 mm Hg
What does Henry’s Law say about the solubility of a gas in a liquid (what is it dependent on)?
Depends on the
- temperature
- partial pressure of the gas over the liquid
- nature of the solvent
- nature of the gas
For a gas, low temp and high pressure increases solubility
What does highly soluble mean?
When dissolved molecules are attracted by water, more can be accumulated without building up excess pressure in a solution.
What does poorly soluble mean?
Molecules which are repelled by water will dissolve less and have lower concentration
What is the rate of net diffusion determined by?
Difference of partial pressures (pp)*
If the pp of gas in the alveoli greater than blood which way will the gas move?
The gas will move into the blood (oxygen)
What is the vapor pressure when a gas mixture is fully humidified at 37 C?
47 mmHg*
What is vapor pressure of water?
Partial pressure of water escaping surface into gas phase
What factors affect gas diffusion rates in fluid?
- Pressure differences
- Gas solubility in fluid
- Area of fluid
- Distance which gas must diffuse
- Molecular weight of gas
- Temperature of fluid
What is diffusion coefficient of the gas?
Characteristics of the gas which affect the ability and rate of net diffusion.
(Solubility/ square root Molecular weight)
What is the limiting factor for gas movement into tissues?
Diffusion rate of gas through tissue water
Respiratory gasses are highly soluble in lipids (cell membranes)
True or False: Alveolar air has the same gas concentration as atmospheric air?
False
Different because alveolar air is partially replaced by atmospheric air during each breath
Normal alveolar ventilation removes half of the gas in ____ seconds?
What about hyper/hypoventilating?
17 seconds
Hyperventilating removes gas faster
Hypoventilating removes gas slower
What is the normal alveolar PO2?
100 mm Hg
What is the normal alveolar PCO2?
40 mm Hg
Alveolar air is expired at ____________
end of exhalation
How thick is the alveolar membrane?
0.6 micrometers
What is the total surface area of the alveoli?
70 square meters
How wide are the alveolar capillaries?
5 micrometers
What are the factors that affect rate of gas diffusion through the respiratory membrane?
What Law?
Frick’s Law
- Thickness of the membrane
- Surface area of the membrane
- Diffusion coefficient
- Pressure difference across the membrane
CO2 diffuses ___ times faster than Oxygen.
20
Oxygen diffuses _______ times faster than Nitrogen.
2
Can the factors which affect diffusion through the respiratory membrane affect the diffusion capacity?
Yes
What is the diffusing capacity?
Volume of a gas that will diffuse through the respiratory membrane each minute for a pressure difference of 1 mm Hg.
What is the diffusing capacity for O2?
21 mL/min/mmHg
How do you get the total quanitity of O2 diffusing across the membrane per minute?
Pressure difference multiplied by the diffusing capacity.
How much does exercising increases the diffusing capacity to?
65 mL/min/mmHg
What increases the diffusion capacity during exercising?
- Recruitment of capillary fields (surface area)
- Better ventilation/perfusion match with blood (All ZONE 3)
CO2 diffusing capacity estimate is based on the ______ _______.
diffusion coefficient
unable to calculate, so based off of this
Diffusing capacity of CO2 at resting is ________ and during exercise is ______?
400 mL/min/mmHg,
1200 mL/min/mmHg
If the V/Q ratio is either zero or infinity there is ______ exchange of gases.
NO
When V/Q = Zero this means what?
There is no ventilation= airway obstruction
Shunt
When V/Q = infinity this means what?
There is no perfusion= PE
Dead Space
Normal deoxygenated blood PO2 is _____..
40 mmHg
Normal deoxygenated blood PCO2 is _____.
45 mmHg
Inspired air PO2 is ______ mmHg
150 mmHg
713mmHg (ppAir)*0.21= 150mmHg
Inspired air PCO2 is ______mmHg.
0 mmHg
What happens in emphysema?
Dissolution of many alveolar walls to coalesce alveoli into larger chambers (surface area decreases up to 5-fold)
Can effect gas diffusion rate through respiratory membrane d/t decreasing surface area
Normal alveolar partial pressures:
Alveolar PO2:____mmHg
Alveolar PCO2: ___mmHg
100 mmHg
40 mmHg
Perfusion, but no ventilation?
V/Q is ____ normal?
Physiologic Shunt- total amt blood shunted/min
Below/ 0
Ventilation, but no perfusion?
V/Q is ____ normal?
Dead space
Above/ Infinity
