L17-Alveolar Gases Flashcards
(27 cards)
What are the 2 main mechanisms of fluid movement.
- Diffusion
- Convection
Features of Diffusion
-Diffusion is down a concentration gradient rather than down a hydrostatic pressure gradient.
-Common in sites with gaseous exchange in alveoli, capillaries.
-O2 will move from alveoli into the pulmonary capillaries and CO2 moving the opposite way from the pulmonary capillaries into the alveoli. Also in capillaries in the tissues around the body as it is how O2 leaves the capillaries and go into the mitochondria. And that CO2 released in the mitochondria is going to diffuse back into the capillaries to come back to lungs to be breathed out.
-used to move O2/CO2 over short distances around the body only.
-Fick’s law of diffusion
-large cross-sectional area
-low velocity
Features of Convection
-convection relies on bulk movement of fluid.
-Mass transfer by bulk motion( high pressure to low pressure) down a pressure gradient.
-CVRS :- moving whole fluid around by convection.
Renal :- hydrostatic pressure.
-Flux = velocity x concentration.
-sites :- conducting airways, larger blood vessels.
-used to move O2/CO2 LONG distances around the body only.
-small cross-sectional area
-high velocity - too fast in the conducting zone for gas exchange/diffusion to occur.
How is convection and diffusion is distributed from arteries to arterioles to venules ?
- for larger blood vessels - from arteries to arterioles - use CONVECTION to move the blood around with the hydrostatic pressure gradient.
- Then when we reach to capillaries in tissues O2 & CO2 will move in and out of the capillaries by DIFFUSION.
- These capillaries will drain back into the venules and the veins in the venous side of the circulation and back into CONVECTION again.
What does convection flow depends on ?
Pressure gradient
What does diffusion depends on ?
concentration gradient
What happens to velocity and airflow when the branching increases as we move down the respiratory zone?
slower airflow - As the total cross-sectional area increases, the velocity of airflow decreases, facilitating efficient gas exchange at the alveolar level.
How can we enhance diffusion using cross sectional area of tubes.
Lots of small tubes running in parallel can be add up to make a larger total cross-sectional area.
-This large combined area provide an extensive surface for O2 and CO2 to diffuse between the lungs and blood.
How many generations of airways in total?
23 generations
How many generations of airways in the
Conducting zone is first 16 generations
AND
Generation 17- Transition point
AND
respiratory zone from 17 to 23.
As the total area increases, the velocity decreases so why does the total flow/flux will remain constant.
maintains a steady overall supply
OR
amount of flow is not changing, its just the speed slowing down.
Why does total flux increases with S.A ?
Total flux 👆 ses with the s.a because total diffusion flux is the rate of diffusion times by total surface area. So we need a large s.a and the conc.gradient to support the gas movement. Total flux is also inhibited/inversely proportional to the thickness of the membrane.
What does partial pressure depends on ?
-Partial pressure depends on how easy the gas diffuses and this is called Diffusivity.
-O2 and CO2 are not equally as diffusible and this impacts the amount of diffusion that goes on.
Explain the term diffusivity. along with the solubility of a gas.
Gas movement for an individual gas is easier. Gases with larger molecular mass move at a slower rate. When moving from gas in the alveoli into the capillary it goes into a solution. So the solubility of the gas is another factor.
CO2 moves slower than O2 due to the Carbon ion making it bigger. Without the carbon ion it is 20x more diffusible than O2.
CO2 is much more soluble even though its partial pressure in the plasma is much less. There’s actually a lot more of CO2 dissolved in plasma because it’s so much more soluble
Explain the diffusion distance between alveoli and capillary in more detail.
Diffusion occurs between alveoli and capillaries.
Diffusion distance is between the alveolar space and across the basement membrane and through the single cells in the capillary. There are multiple capillaries around each alveoli.
Define diffusion reserve in exercise.
-how efficiently the lungs can transfer oxygen into the bloodstream. Lung has to maximise gas exchange to meet the body’s high demand for O2.
-0.25 of a second. it spends less time in the capillary because the blood is moving faster, it’s not going to reach equilibrium until further along that capillary. Here the diffusion reserve is less because its taking longer to reach equilibrium.
What does it mean when you cant breathe while exercising in the highest point?
cardiac cycle is not getting enough oxygen.
OR
CV system can’t get the fluid around the body fast enough to deliver the O2.
What happens with decreased partial pressure gradient like in high altitude?
-Normally, its 1 third way on the capillary to reach equilibrium but bc at a altitude the pressure drops, it takes longer to reach equilibrium.
*****At higher altitude pressure gradient is low so the diffusion gradient is low too!!!! Now its about 2 thirds of the way longer compared to before reaching the equilibrium.
Relationship between alveolar pressure and the partial pressure in the high altitude.
A low partial pressure of O2 in inspired air would result in a lower partial pressure of O2 in the alveolus blood.
Factors that determine the alveolar gas partial pressures?
- venous blood comes in with some O2 and CO2.
- some of this O2 and CO2 will be directed to perfusion.
- alveolar ventilation > brining in O2 or taking out CO2.
Ventilation ……… O2, ventilation …….CO2
adds
removes
Metabolism ……..O2, metabolism …..CO2
removes
adds
What does same levels of ventilation and metabolism gives us?
constant diffusion gradient
If alveolar ventilation remains matched to metabolism then what happens to the alveolar gas compositions?
alveolar gas compositions remain constant.
