Midterm 2 - Gas Exchange Flashcards
why do gases exert pressure on the container
gas molecules are constantly moving/colliding
what is total pressure determined by
the total number of gas molecules per volume unit
what is partial pressure of gases
in a mixture = total pressure x % of that gas
what is partial pressure independent of
other gases present in the mixture
what is the pressure of air (dry)
760 mm Hg
is air in the lungs dry
no
what happens to inspired air
it is 100% saturated with water when it reaches the respiratory zone
what happens to some of the gas molecules when colliding with water
they get dissolved in water which is slightly different than for dry air
what is the relative amount of dissolved gas at equilibrium
constant
what does the relative amount of dissolved gas at equilibrium depend on
solubility and partial pressure of the gas
what does the presence of water do to gas content
dilutes it
at 37 C, what is the water vapour pressure
47 mm Hg
what is the mechanism of gas exchange
passive movement - diffusion
what is the passive movement of gas molecules
from regions of high concentration (partial pressure) to regions of low concentration (partial pressure)
what is the air velocity in alveoli
0
why is the air velocity in alveoli 0
due to large cross sectional area
what is the only way there can be movement from alveoli to alveolar-capillary membrane
diffusion
what is constant in alveoli
atmospheric partial pressures
what does the diffusion of gases depend on
alveolar and blood partial pressures
what does partial pressure in alveoli depend on
ventilation (how much air replaced in alveoli)
what does partial pressure in blood depend on
tissue consumption
what has a significant impact on diffusion
at higher altitude, pO2 in atmosphere decreases
what is pCO2 in atmosphere lower than
lower in both alveoli and blood
do changes in atmospheric pressure impact CO2 diffusion dramatically
no, unless in enclosed space
what does gas exchange work between
alveoli and blood capillary network
where is the blood in the capillaries coming from
the right ventricles
are all capillaries in the lung coming from right ventricle
no - some capillaries are from left to bring oxygen to lung tissue
what is the pO2 of blood entering alveolar capillaries
low
where does O2 diffuse
from alveoli to blood
where is pO2 the same in blood and alveoli
at the end of capillary
where is pCO2 higher
in blood entering capillary then diffuses out towards alveoli
what are the main determinants of gas exchange
driving partial pressure gradient
surface area available for diffusion
thickness of the air-blood barrier
physical properties of gas
what happens when surface area is increased
more exchange
what can capillaries do during exercises to increase exchange
open
what happens during deep inspiration during exercises
the distance between alveoli and capillary endothelium is reduced
what does perfusion correspond to
blood entering the lung
what has to happen for optimum gas exchange
need to match ventilation with the blood flow
for bipeds (humans) at rest, is gas exchange optimum
no
what impact does gravity have on gas exchange in bipeds
perfusion (blood flow) is lowest at the top of the lung (capillaries can collapse) - not so pronounced for ventilation
is gas exchange better for bipeds or quadrupeds
quadrupeds
what is V/Q
term used for ventilation/perfusion
what is V/Q in humans
0.8
when does V/Q become more uniform
during exercise - more blood is pumped throughout lung
what can cause V/Q inequality
certain diseases which can affect V or Q of certain alveoli
what is the natural mechanism that minimizes impact of V/Q inequality
hypoxic vasoconstriction
what does hypoxic vasoconstriction do
closes poorly ventilated alveoli
redirects blood towards well ventilated alveioli
what initiates hypoxic vasoconstriction
reduction of pO2 and/or increase in pCO2 in the interstitial fluid of affected areas
what can cause impaired pulmonary gas exchange
thickening og alveolar-capillary membrane
high altitude or low air pO2
hypoventilation
ventilation-perfusion inequality
what is the consequence of a thickened alveolar-capillary membrane
increases the time for diffusion across the membrane and decreases the rate of diffusion
what is the consequence of high altitude or low air pO2
decreases alveolar oxygen pressure, hence decrease driving pressure
what is hypoventilation
inadequate ventilation of lung
what is V/Q inequality
ventilated alveoli with no blood supply or vice versa
what does gas exchange in tissues follow
same principle as in alveoli
what is diffusion driven by in tissues
difference in partial pressure
in tissues, what do cells consume/produce
consume O2
produce CO2
what is the blood from the left side of the heart loaded with
O2
where does diffusion of O2 occur in tissue
from blood to interstitial fluid to the cells
where does the diffusion of CO2 occur in tissue
from the cell to the interstitial fluid to the blood
