Lecture 11 - Alveolar Gas Exchange Flashcards
what factors does alveolar gas exchange depend on
perfusion and ventilation
what is perfusion
blood to lungs
What is the average ventilation rate to the lungs
7L/min
what determines air flow in the lungs
ohms law; pressure gradient/resistance = airflow
which parameter of air flow into lungs is most effective and most changed by the body
resistance for which radius is the main determinant
What is the partial pressure of oxygen in air
160 mm Hg; oxygen is 21%
What is the partial pressure of O2, CO2, and H20 in alveolar gas
100; 40; 47
the amount of gas that can dissolve in a liquid is determined by
henry’s law
what is the PO2 and C02 in arterial blood and venous blood
Art
- O2 = 95
- PCO2 = 40
Ven
- PO2 = 40
- PCO2 = 46
What controls the O2 concentration in the alveoli
rate of new air in lungs
rate of absorption into blood (250 ml/min)
Why is alveolar gas exchange slow
only about 1/7 of the volume of air that is in the lungs is “new” air
What is 95% of the surface area in the lungs
type 1 pneumocytes where gas exchange occurs
what do type 2 pneumocytes do
secrete surfactant; reabsorb water and Na
What is the rate of gas exchange inversely proportional to
thickness
how does CO2 diffuse compared to O2
20x faster
how much gas is exchanged each minute
250ml O2 and 200ml of CO2
the diffusion of gases
doesn’t not depend on other gases
what are the limitations on diffusion
surface area available, thickness, solubility of gas, pressure gradient
what determines available surface area for gas exchange
number of alveoli available
what can negatively affect surface area in the lungs
damaged or ruptured alveoli such as that in emphysema
what determines the thickness in the lungs
fluid layer, alveolar epithelium, intersitial space, blood vessel wall
which area of the lung is susceptible to thickness changing
collagen deposition in interstitial space
what element of diffusion changes most with exercise?
pressure gradient of gases
in about what time does blood become sat with o2 in lungs
.25 sec
what is a common limiter of perfusion? diffusion
perfusion-N2O; rapidly increases for Pc=PA
diffusion-CO; Pc=/=PA diffusion is limited
how is diffusion capacity of lung measured
inhaling CO; hold for 10 sec; used as a correction factor in DLO2=1.23 x correction factor
Surface tension affects which alveolus primarily
in large alv, radius is large so pressure is low
in small alv, radius is small so pressure is high
air flows into larger alveolus (pressure gradient higher) causing the small one to want to collapse
what is the content of surfactant
80% phospholipids; 10 neutral lipids (cholesterol); 10% surfactant apoproteins
where is surfactant stored in cells
immature lamellar bodies
where is surfactant secreted from in cells
mature lamellar bodies
where is used surfactant recollected in cells
MVB
