lecture17: diffusion of o2 and co2 Flashcards
what is the formula for ventilation perfusion ratio
ventilation-perfusion ration=Va/Q
va=alverolar ventilate rate (ml/min)
Q= rate of pulm blood flow (ml/min)
what is something that would create a decreaing VP ration
a physiological shunt: inaqedate air flow but good blood flow
=high concentration of PCO2 beacuse there is an icnnrease of CO2 in the blood beacuse of bad air flow but not expelled because of the blockage
what is something that increases the VP ratio
if there is a blocked vessel/physiological dead space
=fully functional lungs with good air flow but not enough blood for gas exchange
true or false: in a physiologic dead space, gas exchagne is possibleF
false it is not possible
the part of the respiratory portion where gas should happen, but isnt, is called what
physioollic dead space
what is the VP ratio for physiologic dead space
Va is adequate but Q is low
ventilation in a physiooligc dead space is BLANK
wasted
when Va is adequate but Q is low and ventilation is wasted, what does that contribute to
physiologic dead space
what happens when the physiologic dead space is large
much of the work of breathing is wasted
is there a greater physiologic dead space at the base of the lugs or the apex
at the apex
what is the VP ratio in a physiologic shunt
When VA/Q is below normal (i.e. inadequate VA), certain
fraction of venous blood passes through pulmonary
capillaries without getting oxygenated
what happens when there is inadequate Va in a physiologic shunt
certain fraction of venous blood passes through pulmonary capillaries without getting oxygenated
what is the fraction of venous blood that passes through pulmonary
capillaries without getting oxygenated called
shunted blood
what is shunted blood
fraction of venous blood passes through pulmonary
capillaries without getting oxygenated
Total quantitative amount of shunted blood per minute is
called BLANK
“physiologic shunt”
the greather the physiolofic shunt the greater the BLANK
the greater the amount of blood that fails to be oxygenated as it passes
through the lungs
true or false: physiologic shunt is a type of physiologic shunt
IDK WTF THIS QUESTION WAS
true
at the apex of the lungs, is the VP ratio too high or too low
it is 2.5x greater than the ideal value
At the top of the lung VA/Q is 2.5x greater that as the ideal value = which means it is what type of space.
physiological dead space (i.e. more alveoli are being ventilated than perfused)
at the base/bottom of the lungs, is the VP ratio too high or too low
too low
there is too little ventilation in relation to
blood flow, VA/Q is as low as 0.6x the ideal value
in the area at the bottom of the lungs, a small fracttion of the blood falls to become normally oxygenated… why
there is too little ventilationn in relation to blood flow
=physiologic shunt
durinng exercise, is the physiological dead space decreased or incresed
it is decreased (more blood flow to apex) and inncrease breathing to lungs
explain how the VP ration is mismatching/opposing at the top vs bottom of the lungs
– At the top of the lung VA/Q is 2.5x greater that as the ideal value = physiological dead space (i.e. more alveoli are being ventilated than perfused)
– At the bottom of the lung, there is too little ventilation in relation to blood flow, VA/Q is as low as 0.6x the ideal value. In this area, a small fraction of the blood fails to become normally oxygenated = physiological shunt
why is there bad blood flow but good ventilatio nat the apex of the lungs
gravity sends the blood downwards
what is the next step once the alveoli is venttilated with fresh air
next step in
respiratory process is diffusion of O2 from alveoli into pulmonary blood and diffusion of CO2 in opposite direction
what does diffusion of O2 from alveoli into
pulmonary blood and diffusion of CO2 in opposite direction depend on
– Concentration of ambient air
• 20.9% O2, 78.6% N2, 0.04% CO2
– Pressure of ambient air
what is diffusion
randpom melcules of molecules
are the gases involved in respiratory physiology different from other gases molecules in the body
no tthey are l ike other
gases dissolved in bodily fluids and tissues) = simple
molecules, free to move among each other
what is needed for diffusio nto occur
an energy source is needed;
provided by kinetic motion of molecules themselves
what is the energy source for diffusion
kinetic motion of molecules themselved
the gas molecules do Linear movement at high velocities until collision; then
bounce away in other direction until other collision
which means what in terms of velocity of the particles
– This means that molecules move fast and randomly
what are gas pressures caused by
Caused by impacts of moving molecules against surface
if there are more impacts of moving molecuels against the surface, is there higher or lower pressure
higher
the air inspired innto the alveo is a mix of different gases: name some
oxygen
nitrogen
carbon dioxide
others: he and water
what is the gas partial pressure
Pressure caused by each gas alone is called partial
pressure (Px)
• E.g., PO2, PN2, PCO2
what is the diffusion ratte of each gas directly proportionnal to
Diffusion rate of each gas is directly proportional to its
partial pressure gradient (concentration)
Total gas pressure of a mixture of gases (Ptot) equals what
the sum of the partial pressures of all gases
=dalton law
what is daltons law
Total gas pressure of a mixture of gases (Ptot) equals the sum of the partial pressures of all gases
Dalton’s Law: Ptot = PO2 + PN2 + PCO2 + Pother
does gas dissolved in water exert its own partial pressure like gases on air
xYES
Gas dissolved in water and tissues exerts its
own partial pressure on surface of membrane in
same way as gas does in gas phase
what is partial pressure oof a dissovled gas depend on
Partial pressure of a dissolved gas is determined
not only by its concentration, but also by its
solubility coefficient
what is the formula for partial pressure of a dissolved gas
partial pressure =
concentration of dissolved gas/solubility coefficent
what is the sollubility coefficient
how easy the molecule can go from a gas to diffuse versionn
=Measure of electro-chemical attraction that a dissolved gas has to
water molecules
what is henrys law
The mass of a gas
that dissolves in a fluid at a given temperature varies in direct proportion to the pressure of the gas over the liquid
what are the 2 factors that govern the rate of gas diffusion into a fluid
– The pressure differential between the gas above the fluid and the gas dissolved in the fluid
– The solubility of the gas in the fluid.
if there is more pressure on the gas molecules what happens
increased pressure, more gas molecules in solutionn get dissolved
what happens if there is a high attraction between a dissolved gas to water molecules
high solubility of gas, i.e more gas molecules can
be dissolved before partial pressure of that gas within the solution
increases
which respiratory gas has a higher solubility coefficent
O2 or CO2
CO2
CO2 is 24 times more
soluble than O2 in fluid
CO2 is BLANK times more
soluble than O2 in fluid
24 TIMES
sinnce co2 is 24 times more soluble than o2…
for the same partial pressures on the same side of membrane, we would end up with 24x less or more co2 on the opposite side
24 times more co2 onn opposite side of membrane
what are the factors (5) that affect diffusion rate through respiratory membrane
pressure, cross sectionnal area, distance
sollubility
MW
what is the formualtion for net fiffusion rate (D) across tissue
D is proportional do
delta P x A x S) / (d x square root MW
if pressure icnreases, what happens to net diffusion rate of gases across tissue
increses
if cross sectionnal area increases, what happens to net diffusion rate of gases across tissue
increase
if solubility increases, what happens to net diffusion rate of gases across tissue
increases
if distance increases, what happens to net diffusion rate of gases across tissue
decreases
if molecular weight increases increases, what happens to net diffusion rate of gases across tissue
decreases
what is the diffusion coefficent of a gas
s/squar root of MW
if you have an increases MW it is more or less diffocult to permeate
more difficult
how many layers are there of the respiratory membrane
1 fluid layer and 5 membranes
what are he layers of the respiratory membrane
- Fluid and surfactant layer (in alveolar
lining) - Alveolar epithelium composed of
epithelial cells - Alveolar epithelial basement membrane
- Thin interstitial space between alveolar epithelium and capillary membrane
- Capillary basement membrane
- Capillary endothelial membrane
what is the parttial presssure difference
Partial pressure difference between two sides of the
membrane (ΔP), that is, the difference between the
gas in alveoli and the gas in pulmonary blood
what is partial pressure difference a measure of
It is a measure of the net tendency for gas molecules to move through the membrane.
hwo does CSA of the respiratory membrane decrease
- Removal of lung tissue (if entire lung, A decrase by half)
* Loss of alveolar walls in emphysema (5-fold decrease in A)
when total SA is reduced to 1/3 - 1/4 of normal what happens to gas exchange.
gas exchange through the membrane is significantly impeded even under resting conditions
true or false: in strenous exercise, the slightltest decrease in surfance area doesnt matter
false
In strenuous exercise, the slightest decrease in surface area of the lung can be a serious detriment to gas exchange
the distance of diffusion is relaetd to what
membrane thickness
how does membrane thickness icnrease
- Edema in interstitial space of membrane and in alveoli
* Fibrosis of lung caused by pulmonary diseases
does icnrease the distance of diffsuonn (thickness of membrane) affect gas exchange>
Increase thickness to > 2-3 times normal significantly affects the exchange of gases
the diffusion coefficent of each gas through a membrane depends on what
Depends on gas solubility in the membrane (S) and on its molecular weight (MW)
explain diffusion of O2 bectween gas phase in alveroli and dissovled pahse in blood
– PO2 in gas phase in alveoli (PAO2)»_space; PO2 dissolved in blood (PaO2)
– Net diffusion of O2 is from alveoli to pulmonary arterial blood
explain diffusion of CO2 bectween gas phase in alveroli and dissovled pahse in blood
– PCO2 in gas phase in alveoli (PACO2) «_space;PCO2 dissolved blood (PaCO2)
– Net diffusion of CO2 is from pulmonary arterial blood to alveoli
is –PO2 in gas phase in alveoli (PAO2) greater or lesser than PO2 dissolved in blood (PaO2)
greater
SINCE PO2 in gas phase in alveoli (PAO2)»_space; PO2 dissolved in blood
(PaO2), what is the directionn of net diffusion of O
Net diffusion of O2 is from alveoli to pulmonary arterial blood
why is Net diffusion of O2 is from alveoli to pulmonary arterial blood
because PO2 in gas phase in alveoli (PAO2)»_space; PO2 dissolved in blood
(PaO2)
is PCO2 in gas phase in alveoli (PACO2) greather than or lesss than PCO2 dissolved
blood (PaCO2
less than
since PCO2 in gas phase in alveoli (PACO2) «_space;PCO2 dissolved blood (PaCO2), what is the direction of net diffusion of co2
Net diffusion of CO2 is from pulmonary arterial blood to alveoli
why Net diffusion of CO2 is from pulmonary arterial blood to alveoli
PCO2 in gas phase in alveoli (PACO2) «_space;PCO2 dissolved
blood (PaCO2)
what are the 2 things that Oxygen concentration and partial pressure of O2 in alveoli (PAO2) depend on
– Alveolar ventilation (rate of new O2 inspired into alveoli)
• Increase of alveolar ventilation increases O2 concentration
(CAO2) and PAO2
– Rate of absorption of O2 into blood
• Increase of O2 absorption rate decreases CAO2 and PAO2
what is alveolar ventilattionn
rate of new o2 inspired into alveroli
if there is an increase of alveolar ventilation, what happens in terms of o2 concentration
Increase of alveolar ventilation increases O2 concentration
(CAO2) and PAO2
an increase of 02 absorption increases or decreases CAO2 and PAO2
decreases
what is a normal Va
4.2 L/min
what is normal o2 absorptiom rate
250 ml 02 per min
what is normal Pa O2 levels
104 mmHG
If O2 absorption increases to 1000 ml/min (as during moderate exercise), what increase is needed in VA to maintain pressure levels
4x increase in VA required to maintain same PAO2
know graph on slide 22
.
The CO2 concentration (CACO2) and PCO2 in alveoli (PACO2) depend on what 2 things
– Excretion rate of CO2 from pulmonary arterial blood into alveoli
• Increase of CO2 excretion rate increases CACO2 and alveolar PACO2
– The rate of alveolar ventilation to expire CO2
• Increase of ventilation rate decreases the alveolar PACO2 and CO2
concentration (CACO2)
if there is an icnrease CO2 extretion rate, what does that do to CaCO2 and alveolar PaCO2
increases
if there is an Increase of ventilation rate what does that do to the alveolar PACO2 and CO2
concentration (CACO2)
decreases
an increase in ventilation means an increase of decrease parttial pressure of c02
decrese partial pressure
if there is an increase in metabolism (ie. increase co2 production) what do you need in order to excrete that co2
need a higher ventilation to excrete co2
what is the function of dead spalce
allows us to mainfain normal concentration of gases (evens concentrationn changes between inhale and exhale)
know graph on slide 25
.
true or false: inhaled air changes through respiration
true
explain tracheal air
Air completely saturates with water vapor as it enters the nasal cavities/mouth
and passes down the respiratory tract
what happens to the effective PO2 in tracheal air
decreases by about 10 mmHG from ambient value
does humidification affect inspired PCO2
no beacuse of its neglible contribution to inspired air
explain how the PO2 decreases when going from ambient to tracheal air
becuse total partial pressure remains even with the addition of water so the other gases partial pressure needs to derases
ttrue or false: tracheal air and alveolar air are the same composition
false
explain why alveolar air diffurs from incoming breath of moist tracheal air
Alveolar air composition differs from the incoming breath of moist ambient air
because CO2 continually enters the alveoli from the blood: 14.5% O2, 5.5% CO2,
and 80.0% N2
o2 travels from higher to lower pressure as what (from what to what region)
as it dissolved and diffuses through the alveolar membranes in to the blood
true or false: CO2 exists under a slightly greater pressure in returning
venous blood than in the alveolis
true
since CO2 exists under a slightly greater pressure in returning
venous blood than in the alveoli, what does that cause
causing net diffusion of CO2
from the blood into the lungs
does N2 change in alveroli capillary gas?
N2 remains essentially unchagned
how long does alveolar gas-blood equilibrum take
takes place inn 1/4 sec
what are the factors that impair gas transfer capacity att the alveolar capilarry membrane
– Buildup of a pollutant layer that “thickens” the alveolar membrane
– Reduction in alveolar surface area
– Low perfusion
what is the average functional residual capacity
2300 ml
explain the concept of slow replacement of alverolar air
– Average functional residual capacity (FRC) ~ 2300 ml
– Yet only ~350 ml of new air per normal resting breath is brought into alveoli
– Means that only ~ 1/7 of total air remaining in lungs is replaced with new air with each breath
– Rate of removal of excess gas from alveoli depends on rate of alveolar ventilation (VA)
true or false: all the total air remaining in lungs is repalced with new air each breath?
faslse
Average functional residual capacity (FRC) ~ 2300 ml
– Yet only ~350 ml of new air per normal resting breath is brought
into alveoli
– Means that only ~ 1/7 of total air remaining in lungs is replaced with
new air with each breath
the rate of removal of excess gas from alveroli depends o nwhat
rate of alverolr ventilation
why is slow replacement of alveolar air importatnt
Slow replacement is important in preventing sudden changes in
gas concentrations in blood
= stabilizes respiratory controlmechanisms
net difussion occurs from high concentration area to low concentration area or opposite
high to low
molecules bouncing in one direction minus those bouncing in opposite
direction, is called the BLANK
pressure difference
true or false: molecules bouncing in one direction minus those bouncing in opposite
direction, aka pressure difference will cause diffusion
true
Net rate of diffusion in fluids is affected by pressure difference +
several other factors like what
- Solubility of gas in fluid
- Cross-sectional area of fluid
- Distance through which gas must diffuse
- Molecular weight of gas
- Temperature of fluid (in body, remains constant)
explain gas transfer in tissues
• At rest, PO2 in the fluid outside a muscle cell averages 40 mm Hg and intracellular PCO2 averages 46 mm Hg
• In vigorous exercise, PO2 within muscle tissue falls
toward 0 mm Hg, the PCO2 approaches 90 mm Hg
- Pressure differences between gases in plasma and tissues establish diffusion gradients
- O2 leaves the blood and diffuses toward cells, while CO2 flows from cells into the blood
• Blood then passes into the venous circuit for return to the
heart and delivery to the lungs
