Pulmonary Gas Exchange Flashcards
Components of air and their relative concentrations
Atmospheric pressure:
- 78.09% nitrogen
- 20.95% O2
- 0.93% Argon
- 0.03% CO2
Components of air at alveoli saturated with 6.18% water vapor
- 73.26% Nitrogen
- 19.65% O2
- 0.87% argon
- 0.03% CO2
What are the three gas laws
- Dalton’s law
- Boyle’s law
- Henry’s law
What is Dalton’s law
The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressure of individual gases
What is Boyle’s Law
For a fixed amount of an ideal gas kept at a fixed temperature, P (pressure) and V (volume) are inversely proportional
What is Henry’s Law
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid directly proportional to the partial pressure of that gas in equilibrium with that liquid
Ideal gas law
P= nRT/V
Pressure is directly proportional to the
concentration of the gas molecules
The rate of diffusion is directly proportional to
pressure caused by that gas alone
A gas dissolved in a fluid also exerts its own ______ against a cell membrane
partial pressure
What is the partial pressure of CO2 at alveolar membrane
0.21 mm Hg
What is the partial pressure of O2 at alveolar membrane
=760x0.197
= 150mmHg
The partial pressure of a gas in solution is determined not only by its concentration but also by the __________ of the gas. This is _____ law
Solubility coefficient, Henry’s
equation for Henry’s law
partial pressure= dissolved gas / solubility coefficient
What is the solubility of oxygen
0.024
What is the solubility of carbon dioxide
0.57
Because carbon dioxide is _____ soluble in water than oxygen, it will exert a partial pressure (for a given concentration) that is ____ than _____ that of oxygen
more, less, 1/20th
______ of water is the partial pressure exerted to escape from the liquid phase to the gas phase
Vapor pressure
What is the vapor pressure of water at normal body temperature (37 degrees C)
47mmHg
Vapor pressure of water depends on the _____ of water. and decreases with
Temperature, decreases with a decrease in temperature
What are the 5 factors that 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 gas
- Temperature of fluid (remains reasonably constant)
What is the functional residual capacity of the lungs of the average man
2300mL
only ____ mL of new air is brought into the alveoli with each normal inspiration, and this same amount of old alveolar air is expired. Therefore, the volume of alveolar air replaced by new atmospheric air with each breath is only ____ of the total (2300mL), so multiple breaths are required to exchange most of the alveolar air
350mL, 1/7th
oxygen concentration in the alveoli, as well as its partial pressure, is controlled by
- Rate of absorption of oxygen into the blood
- Rate of new oxygen entry into the lungs (alveolar ventilation)
to quadruple oxygen consumption, alveolar ventilation must
also be quadrupled
Why can alveolar ventilation not increase PO2 above 149n, Hg under normal conditions
Because this is the maximum PO2 in humidified air at sea level pressure (if the person breathes gases that contain partial pressures of O2 higher than 149mmHg the alveolar PO2 can approach these higher pressures at high rates of ventilation.
At moderate exercise the alveolar ventilation must increase _____ to maintain the normal alveolar PO2 of ____
4x, 104mmHg
Carbon dioxide concentration in the alveoli, as well as its partial pressure, is controlled by
- Rate of carbon dioxide excretion
- Alveolar PCO2 increase in direct proportion to rate of excretion
- Alveolar ventilation
- Alveolar PCO2 decreases in inverse proportion to alveolar ventilation
As Alveolar ventilation increases PCO2
decreases
As PCO2 excretion increases Alveolar PCO2
increases
What is the respiratory membrane (pulmonary membrane)
all terminal portions of the lungs, not merely in the alveoli
Layers of the respiratory membrane
- ) A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of the alveolar fluid
- ) The Alveolar epithelium, which is composed of thin epithelial cells
- ) An epithelial basement membrane
- ) A thin interstitial space between the alveolar epithelium and the capillary membrane
- ) A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane
- ) The capillary endothelial membrane
Components of the Respiratory unit
- Respiratory Bronchiole
- Alveolar ducts
- Atria
- Alveoli
What is the overall thickness of the respiratory membrane
as little as 0.2 micrometers and averages 0.6 micrometers
what is the total surface area of the respiratory membrane of a healthy adult male
about 70 square meters
Factors that determine how rapidly a gas will pass through the respiratory membrane
- Membrane thickness
- Membrane surface area
- Diffusion coefficient of gas in the substance of the membrane
- Partial pressure difference of gas between the two sides of the membrane
any factor that increases membrane thickness (ex. Edema or fibrosis) to more than ____ or ____ normal can interfere with gas exchange
2x or 3x
Ventilation-Perfusion ratio
Va/Q= alveolar ventilatio/blood flow
What is normal ventilation-perfusion ratio
0.8
ventilation= 4L/min / (pulmonary blood flow=5L/min)
Gas exchange is complete in _____ of capillary
initial third
what is normal alveolar CO2
40
What is normal alveolar O2
100
VA/Q equals 0 when Va=____ but there is still perfusion
0
what is the reason for Va/Q=0
-due to airway obstruction (i.e. mucus plug)
What happens to blood gas when Va/Q=0
Blood gas composition remains unchanged. This means it is the same O2 and CO2 as it was when it entered the capillary as when it comes out
When is Va/Q equal to infinity
when Q=0, thus meaning there is still no ventilation (no gas exchange)
- due to vascular obstruction ()i.e. Pulmonary embolism)
What happens to alveolar gas composition when Va/Q is equal to infinity
Alveolar gas composition remains unchanged(stays same as atm levels) because there is no blood contact. This creates a physiologic shunt
Normal Alveolar perfusion PO2= and PCO2=
PO2= 104 mmHg PCO2= 40 mmHg
The greater the physiological shunt, the _____ the amount of blood that fails to be oxygenated
greater
Explain the physiologic shunt
Whenever Va/Q is below normal a certain fraction of the venous blood passing through the pulmonary capillaries does not become oxygenated. Also some blood is also shunted through bronchial vessels rather than through alveolar capillaries
The greater the physiologic shunt, the greater the amount of blood that fails to be oxygenated
Physiological dead space
- Sum of wasted alveolar ventialation (this is caused form great ventilation and poor blood flow leading to more oxygen available than can be transported by blood) plus anatomic dead space
What is PO2 and PCO2 when Va/Q=0
PO2=40
PCO2=45
What is PO2 and PCO2 when Va/Q=infinity
PO2=149
PCO2= 0
