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Unformatted text preview: Gas Exchange Air is a mixture of gasses: 78% N, 21% O, 1-3% CO2, with variable levels of H2O Common features of respiratory surfaces: wet, thin, large surface area, blood brought close Partial Pressure= Total Pressure * Percent Time is proportional to Distance 2 Alveoli are where gas exchange occurs (thin walls, surrounded by capillaries, lined with coat of water) o When there is thickened fluid here, as in congestive heart failure, gas exchange is impaired o Thin epithelial cells secrete surfactant , which reduces surface tension in the alveoli almost to zero by reducing hydrogen bonding of water molecules o Premature babies have problems breathing because secretion of surfactant occurs late in development Breathing o Inhalation: decreased pressure, rib cage moves out (inner intercostal muscles contract) and diaphragm contracts and moves down o Exhalation: increased pressure, rib cage moves in (inner intercostal muscles relax) and diaphragm contracts and moves up, higher pressure in the lungs as a result of decrease in chest volume when elastic proteins in the tissue in between alveoli recoil and shrink lung and residual surface tension in alveoli o When the alveoli inflate during inhalation, they get bigger and surface area gets bigger, so surfactants are spread out and less effective in reducing surface tension, which causes them to...
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- Spring '09