Pulmonary Gas Exchange Flashcards
What is Dalton’s Law?
Ptotal of non-reactive gases = sum of partial pressures of individual gases.
What is Boyle’s Law?
P = 1/V
For a fixed amount of an ideal gas kept at a fixed temperature.
What is Henry’s Law?
At a constant temperature, the amount of a gas that dissovles in a type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
What is the ideal gas law?
P = nRT/V
What is the partial pressure of oxygen at the alveolar membrane?
150 mm Hg
What is the partial pressure of gas determined by?
concentration and solubility coefficient of the gas.
Partial pressure = [dissolved gas]/solubility coefficient
What are the major components of the air?
Nitrogen (78%)
Oxygen (21%)
Argon (0.93%)
Carbon dioxide (0.03%)
Pressure is ___ proportional to the concentration of gas molecules.
directly
What is the vapor pressure of water?
The partial pressure exerted to escape from the liquid to the gase phase.
At normal body temperature, vapor pressure = 47 mm Hg
What is vapor pressure dependent upon?
temperature of the water
What factors affect rate of gas diffusion in a fluid?
solubility of gas in the fluid
cross-sectional area of the fluid
distance through which the gas must diffuse
molecular weight of the gas
temperature of fluid
HOw do the solubility coefficients of oxygen and carbon dioxide compare?
Solubility of oygen = 0.024
Solubility of carbon dioxide = 0.57
Because carbon dioxide is more soluble in water than oxygen, it will exert a partial pressure that is less than 1/20th that of oxygen.
What are the factors that control oxygen concentration in the alveoli?
Rate of absorption of oxygen into the blood
Rate of new oxygen entry into the lungs.
Why can alveolar ventilation not increase pO2 above 149 mm Hg under normal conditions?
Too high of a level of alveolar ventilation is needed.
What are the facotrs that control carbon dioxide concentration in the alveoli?
Rate of carbon dioxide excretion (pressure increases in direct proportion to excretion)
alveolar ventilation (alveolar PCO2 decreases in inverse proportion to alveolar ventilation).
What are the components of the alveolar respiratory membrane?
capillary endothelium
capillary basement membrane
interstitial space
epithelial basement membrane
alveolar epithelium
The respiratory membrane allows for the diffusion of what gases?
oxygen and carbon dioxide
What factors determine how rapidly a gas will pass through the respiratory membrane?
membrane thickness
membrane surface area
Diffusion coefficient of gas
partial pressure difference of gas between two sides of the membrane.
What does the Va/Q ratio refer to?
It is a ratio of ventilation-perfusion
When is the Va/Q ratio normal?
When both factors are normal for a given alveolus.
What is the normal Va/Q ratio?
0.8
This indicates gas exchange is complete in initial third of capillary.
What occurs when Va/Q = 0?
There is still perfusion, but there is an airway opstruction.
Blood gas composition remains unchanged.
What occurs when Va/Q = infinity?
There is still ventilation, but no gas exchange.
This is due to a vascular obstruction (i.e. pulmonary embolism).
Alveolar gas composition remains unchanged because there is no blood contact. This creates a physiologic shunt.
What is shunted blood?
venous blood passing through pulmonary capillaries that does not become oxygenated.
It ocurs whenever Va/Q is below normal.
The greater the physiologic shunt, the ___ the amount of blood that fails to be oxygenated.
Greater
What occurs when ventilation of some of the alveoli is great but alveolar blood flow is low?
There is far more available oxygen in the alveoli than can be transported away from the alveoli by the flowing blood. The ventilation of these alveoli is wasted.
What is the physiologic dead space?
The sum of oxygen transported (When there is an exess of oxygen) + anatomic dead space
