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Unformatted text preview: Lecture 8: Exchange and Transport of Respiratory Gases • General : o Exchange : movement of gases across barriers o Transport : carriage of gases in the blood • Diffusion (exchange) of Gas Across a Barrier o there are barriers to diffusion o what influence the rate of movement in both directions Surface Area Thickness o A) Homogeneous Barrier Determines flow in both direction : • SA of membrane • concentration of partial pressure differences of gasses • thickness/width of membrane Net flow : occurs when flow in one direction exceeds flow in other o B) Alveolar Wall Must consider moisture lines alveoli: • includes necessity that gas is soluble in that liquid • we have to know solubility constant of gas Henry’s Law according to Henry’s Law, • amt of oxygen dissolved in liquid layer = [solubility Oxygen X its partial pressure Oxygen ] • Thickness of Diffusion of Gas o Thicker barrier = slower diffusion of gas o Top vs Bottom picture: bottom • thinner barrier steeper slope faster diffusion Top: • thicker barrier longer slope slower diffusion • produces low flow • Multiple Diffusion Barriers for Alveolar Oxygen to Pass o shows multiple layers between alveolar layer and pulmonary capillary blood 3 important layers: • type 1 alveolar cells • interstitial space o separates alveolar epithelium from endothelium • capillary endothelium these layers make up barrier to diffusion each segment has its own diffusion properties • D1-D12: suggest each layer has different diffusion properties o D M : all of them summed is the diffusion property of membrane Slide 1 Slide 2 Slide 3 Slide 4 o : oxygen binding to Hb from OxyHb o D L : total diffusion capacity of the lung o Vc = volume of blood in pulmonary capillaries o theta: rate of uptake by Hb described by: volume, concentration, partial pressure • Limitation of Diffusion and Perfusion: o there are limitation o perfusion : rate of blood flow o A) diffusion limited exchange of gas (left) uses low concentration of carbon monoxide • binds to Hb o A) perfusion limited exchange of gas (right) uses nitrous oxide • doesn’t bind to Hb o B) Partial Pressure of Carbon Monoxide in Alveolar Air [Limitation] slope of both curves: Carbon M in blood never reaches equlibrium with Carbon M in alveolar air • rate of diffusion across barrier is so slow and bound by Hb that the free CO in solution could never reach the alveolar concentration • CO doesn’t reach equilibrium with air CO goes to capillary w/o reach equilibrium o B) Partial Pressure of Nitrous Oxide in Alveolar Air [Limitation] represent nitrous oxide in alveolar air • Hb doesn’t bind so it stays in the solution • amount of nitrous oxide quickly equlibrates with N2O in...
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- Fall '08
- Partial Pressure