PL4 - pulm diffusion and gas exhange Flashcards
Alveolar ventilation - define
It’s the volume of fresh air entering the alveoli per minute
It’s the exchange of gas between the alveoli and the external environment
Is the volume of fresh air and the volume of alveolar air leaving the lungs per minute about the same?
yes
Alveolar ventilation is defined as the vol of fresh air entering the lungs and can also be written as the volume of alveolar air leaving the body per min.
Gas exchange is the process of transferring gases across the alveolar and capillary membranes and it requires both ________ and ___________.
Diffusion of gas
Perfusion of blood
( gas needs to be able to diffuse - and there needs to be blood perfusion of alveoli by capillaries or no gas exchange will occur)
What type of transport is involved in gas exchange? What allows for this type of transport?
Passive diffusion down a partial pressure gradients.
What is meant by partial pressure of a gas?
What are the partial pressure gradients - which way do the gases move in the alveoli
The partial pressure of a gas refers to the pressure exerted by a gas in a mixture on the surface of its container. This pressure would be the same if the gas was alone. (not in a mixture)
The PO2 is higher in the aveoli and lower in the caps (moves out of alveoli into blood)
The PCO2 is lower in the alveoli and higher in the caps (moves into alveoli)
What are the determinants of gas diffusion?
- Membrane characteristics
— Thickness of the barrier
— SA of the alveoli and the capillaries and ventilation perfusion matching - Characteristics of the gas
— Molecular weight (Graham’s law)
— Solubility (Henry’s law) - Partial pressure gradient across the alveoli and capillary wall.
What are the layers gas has to pass thru when diffusing into blood caps from the alveoli?
- Layer of surfactant coating alveoli
- Alveolar epithelium (1 cell thick - pneumocytes)
- Basal lamina
- Capillary endothelium
- Plasma
- Erythrocyte
What is the law associated with rate of diffusion in terms of the molecular weight of gas
Graham’s law
What is the law associated with the solubiltiy of gas
Henry’s law
What is Fick’s Law? What does it determine? What factors are involved? What may influence these factors?
Fick’s law determines the rate of diffusion in relation to the SA, Diffusion constant, partial P. gradients and membrane thickness.
It says that the rate of diffusion is directly proportional to:
- the SA of diffusion (Depends on: 1. degree of pulm. alveoli and capillaries 2. ageing or disease (emphysema)
- the diffusion constant
- and the partial pressure gradients
It’s inversely proportional to:
- the thickness of the membrane. (influenced by: 1. age 2. disease (pulm fibrosis)
What is graham’s law? What does it determine?
Determines the rate of diffusion in liquids in relation to the molecular weight of the gas.
It says that when gases are dissolved in liquid the rate of diffusion is inversely proportional to the root of the molecular weight of the gas
Essentially gases with a lower molecular weight diffuse faster
What is henry’s law? What does it determine?
Henry’s law describes the relationship between the solubility of a gas IN A LIQUID and their partial pressure.
Says that the volume of gas that dissolves in unit volume of a liquid at a given temp. is directly proportional to the partial pressure of the gas at equilibrium.
(Essentially increase in solubility/conc. of gas dissolved = increase in partial P. of gas at equilibrium)
For CO2 and O2 answer which one :
- has lower molecular weight
- has greater solubility
- Dissolves at a greater rate and by how much
- O2
- CO2
- CO2 – 22 times more soluble than O2
What is the relative rate of diffusion of CO2:O2 from alveolus to rbcs?
20.7 : 1
At any given partial pressure there would be more _____ dissolved in water compared to ____
more CO2 than O2
How can the PO2 difference between alveoli and pulm capillaries be influenced?
(Partial P of O2 influences its rate of diffusion)
- Fraction of inspired O2 (Fi O2)
- Alveolar ventilation
- Pulmonary capillary blood flow
- Oxygenation of haemoglobin
What is barometric P? How does it change depending on altitude?
The pressure exerted by all the gases in the atmosphere
Decreases as altitude increases
What influences partial P? and what doesnt?
Each gas in the mixture exerts a certain pressure according to:
— Its concentration
This is independent of its:
— size
— other gases present
Parital P?
Individual pressure exerted by any individual gas in a mixture is called partial pressure or Pgas
CO2 is larger than O2 would this affect partial pressure?
no
How would partial pressure of O2 change with altitude?
Increase in altitude would decrease partial pressure of O2
— it is why airplane cabins are pressurised ( a decrease in atmospheric pressure is what causes a decrease in partial P. of O2 – not that there is a decreased amount of O2 available)
What are the variables involved in the alveolar gas equation? What is the equation used to determine?
- Barometric P.
- Partial P. of H2O (air humidified by nasal muscosa)
- Fraction of inspired O2
- Partial P. of CO2
- Respiratory quotient
—» Used to determine the partial pressure of O2 in the alveoli
What is the respiratory quotient? what does it depend on?
It is the amount of CO2 produced and the O2 consumed
It depends on the type of diet:
– pure fat diet = 0.7
– pure carb diet = 1
– average = 0.8
Why does PO2 decrease at higher altitudes?
It decreases due to a decrease in the barometric pressure
The Fraction of inspired O2 (Fi O2) remains the same
Describe the change in the partial pressures of O2, CO2 and H2O as you go down the airway tract.
PO2 –> Decreases (some amount remains in the conducting zone and a slightly decreased amount enters the alveoli – the O2 is then uptaken by caps - decreases further)
PCO2–> Increases (CO2 in caps diffuses into alveoli)
PH2O –> Increases (air is moistened)
How do PO2 and PCO2 levels vary in expired air as expiration progresses?
Initially air in the dead space is exhaled:
——-> there will be a large PO2 in this exhaled air and a low to almost negligible PCO2
The air from the alveoli and the dead space closer to the respiratory zone is then exhaled;
——-> There will be a lower conc of O2/ lower PO2 in this air and a higher CO2 conc./ higher PCO2.
Normal alveolar ventilation? formula?
Its the vol. of air per min involved in gas exchange
What is the partial P. of O2 and CO2 in systemic venous and arterial blood?
Is the amount of O2 supplied to tissues and CO2 taken away from tissues dependent on rate of cellular metabolism? Why?
Yes.
What is emphysema characterised by? Is it reversible?
It’s a progressive and non-reversible disease
Characterised by:
- Muscle wasting
- Barrel chest
- productive cough
- shortness of breath
- increased respiratory rate
- wheezing
- limited physical activity (short of breath even when doing normal every day tasks)
Affect of restrictive and obstructive diseases on FEV1, FVC, FEV1/FVC, FEF 20-75?
Affect of restrictive and obstructive diseases on their flow volume loops?
