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Physiology 3120
Tom Stavraky

Human Physiology Monday, February 1, 2010 “Respiration II” Ventilation • Process by which air moves in and out of the lung • Inspiration/inhalation  Active process; requires contraction of diaphragm muscles and intercostal muscle  Contraction of external intercostals and contraction of diaphragm increases pressure gradient between interpleural space and lungs • Only takes a relatively small change in pressure • Cutting a hole in the diaphragm will interfere with inspiration (interpleural pressure will be atmospheric  Lung inflates because have larger surrounding area • Expiration/exhalation  Passive process normally; lung and chest wall moves back to equilibrium  Active process during exercise or spontaneous hyperventilation; muscles of abdominal wall/internal intercostals; cutting the internal intercostals would prevent voluntary expiration (i.e. won’t be able to exercise) • Lung compliance  Relatively small changes in pressure required to inflate lung  Volume change per unit pressure change  Large = large volume change for small pressure change  Small = small volume change for large pressure change  2 factors  Elasticity of lung tissue • Fibres of elastin (easily stretched) and collagen (not easily stretched) • Specific arrangement of these fibres  Surface tension at alveolar level  Can plot it with a pressure-volume curve  Take lung out, slowly inflate & deflate it and measure the pressure (dog lung)  Initially, you don’t get large increase in volume for a change in pressure; if you continue inflation, get a large volume increase for each pressure interval  Important features: • Nonlinear • At high and low volumes, the lung is less compliant than at intermediate volumes • At the same pressure, the lung has more volume during deflation than during inflation (hysteresis) • Note tha
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