Respiratory System: Gas Exchange and Gas Transport in the Blood Flashcards
What is the process of randomly moving molecules making their way back and forth across respiratory membrane?
diffusion
What is termed the molecular impact on surface?
pressure
What is the term for the pressure exerted by each gas?
partial pressure
- multiple gases in the air
- rate of diffusion directly related to partial pressure of gas
Partial pressure equation
concentration of dissolved gas / solubility coefficient
Direction of net diffusion depends on what? (6)
- pressure difference
- solubility of gas in fluid
- cross-sectional area of fluid
- distance gas must diffuse
- molecular weight of the gas (smaller = better)
- temperature of fluid
Diffusion equation
(change in pressure x area x solubility coefficient) / (distance to diffuse x square root of molecular weight)
Do respiratory gases diffuse across a membrane easily?
yes
What is a limiting factor to rate of diffusion?
water
Rate of diffusion thru tissue is similar to what?
diffusion thru water
What respiratory gas is constantly being absorbed from alveoli?
O2
What respiratory gas is constantly diffusing from blood to alveoli?
CO2
What is humidified in the respiratory tract?
H2O
How many mmHg of O2 in alveoli?
104 mmHg
Amount of O2 in alveoli is controlled by what? (2)
- rate of absorption by pulmonary capillaries
- rate of O2 entry into alveoli via ventilation
How many mmHg of CO2 in alveoli?
40 mmHg
Amount of CO2 in alveoli is controlled by what? (2)
- rate of excretion by pulmonary capillaries
- rate of alveolar ventilation
Increase expiration equals what?
increase expiration = decrease in CO2 = decrease in PCO2
Amount of PO2 in venous blood of capillary?
40 mmHg
Amount of PCO2 in venous blood of capillary?
45 mmHg
The amount of O2 in the alveoli can never exceed what?
149 mmHg @ sea level if breathing normally
– because that is the max PO2 in the system after it has become humidified
Diffusion coefficients for the following: O2 CO2 CO N2 He
O2 = 1.0 CO2 = 20.3 CO = 0.81 N2 = 0.53 He = 0.95
Alveolar air replacement – how much new air goes into the alveoli with each breath?
350 mL
What fraction of alveolar air is replaced by new air with each breath?
1/7
Do we have a quick exchange of O2/CO2?
No – it is a more tempered response to partial pressures
What causes diffusion to be rapid?
large surface area of respiratory membrane w/ small amount of blood spread throughout
Pulmonary capillaries have a large or small diameter?
small diameter
What 4 factors is diffusion affected by?
a. thickness of membrane
b. surface area of respiratory membrane
c. diffusion coefficient
d. pressure difference across membrane
The volume of gas that will diffuse thru the membrane from the lungs to the blood each minute for a partial pressure difference of 1 mmHg?
Diffusion capacity
Diffusion capacity of oxygen at rest? During exercise?
Rest: ~ 230 ml O2/min
Exercise: max 3x diffusion capacity
Diffusion capacity of carbon dioxide at rest? During exercise?
Rest and exercise: increase proportionately to O2 given that CO2 has a diffusion coefficient > 20x of O2
Q =
perfusion
Va =
ventilation