PHGY 210 Lecture Notes - Lecture 8: Slinky, Cardiac Output, Circulatory System
Jan 20, 2017
Types of Alveolar Ventilation
-average PO2 and PCO2 in alveoli (105 and 40, respectively)
-today we’ll be talking about the details of the numbers
Gas Diffusion
Diffusion Rate
-transfer of gases across alveolar-capillary membrane occurs by passive diffusion
-this diffusion is very efficient in lungs b/c of huge surface area of membrane and its
extreme thinness
-diffusion is governed by Fick's Law:
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Ultrastructure of Respiratory Membrane as shown in cross-section
-oxygen has to diffuse through layers before it gets to the RBC
-CO2 has to go in opposite direction through all these layers
Diffusion Rate
-to diffuse through a liquid, a gas must be soluble in the liquid
-amount of gas dissolved is proportional to its partial pressure
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-Henry’s law
-b/c CO2 is considerably more soluble than O2 in water
-it diffuses ~20 times more rapidly than O2
-h/e, difference in PCO2 b/w 2 sides of alveolar-capillary membrane is 10 times smaller than that
for PO2
-therefore, time required for equilibrium b/w alveolar air and capillary blood is ~ same
for the two gases
-oxygen diffuses quickly b/c high gradient
-CO2 diffuses quickly b/c high solubility
-CO2 is so soluble that it is equal
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find more resources at oneclass.com
Document Summary
Average po2 and pco2 in alveoli (105 and 40, respectively) Today we"ll be talking about the details of the numbers. Transfer of gases across alveolar-capillary membrane occurs by passive diffusion. This diffusion is very efficient in lungs b/c of huge surface area of membrane and its extreme thinness. Ultrastructure of respiratory membrane as shown in cross-section. Oxygen has to diffuse through layers before it gets to the rbc. Co2 has to go in opposite direction through all these layers. To diffuse through a liquid, a gas must be soluble in the liquid. Amount of gas dissolved is proportional to its partial pressure. B/c co2 is considerably more soluble than o2 in water. It diffuses ~20 times more rapidly than o2. H/e, difference in pco2 b/w 2 sides of alveolar-capillary membrane is 10 times smaller than that for po2. Therefore, time required for equilibrium b/w alveolar air and capillary blood is ~ same for the two gases.
