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Lung structure & function

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Physiology 3120
Tom Stavraky

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Human Physiology Friday, January 29, 2010 “Respiratory I” Structure & Function of the Lung • Main function of the lung is gas exchange  Occurs by diffusion, which occurs according to Fick’s law of diffusion Vgas= (constant * (P1– P 2) * A/T • A = area  larger area = faster diffusion • T = thickness  bigger thickness = slower diffusion • P 1 P 2 difference in partial pressure  larger gradient = faster diffusion • Constant = diffusion constant  larger = faster diffusion o Proportional to gas solubility but inversely proportional to the square root of its molecular weight  CO out2 O in;2oxygen from atmosphere into blood, carbon dioxide from blood into atmosphere  The area of the lung where diffusion occurs is the blood-gas barrier has thin interface and large area (permits fast diffusion) • Partial pressure = pressure exerted by one gas in a mixture of gases; equal to the total pressure of the gas mixture times the fractional concentration of the gas in the mixture  Partial pressure of a gas in solution  Equal to the partial pressure of the gas in equilibrium with the mixture  Regardless of the solubility of the gas in solution  Partial pressure of oxygen in arterial blood is PaO 2 • Structure  Blood-gas barrier  Very thin (0.5μm thick)  Several cell layers 2  Very
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