KINE 3012 Chapter Notes - Chapter 13.3: External Intercostal Muscles, Intrapleural Pressure, Thoracic Cavity
11 Feb 2018
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Document Summary
Onset of expiration: relaxation of inspiratory muscles: diaphragm assumes its original dome-shaped position when it relaxes, with no forces causing expansion, chest wall & stretched lungs recoil to preinspiratory size, as lung recoil, intra-alveolar pressure rises. In resting expiration, intra-alveolar pressure increases 1mmhg above atmospheric level 761mmhg. Air leaves lungs down its pressure gradient from high intra- alveolar pressure to lower atmospheric pressure. Outward flow ceases when intra-alveolar pressure becomes equal to atmosphere. At end of inspiration & expiration, inta-alveolar pressure= atmospheric pressure. Transmural gradient always exists & lung always stretched (intra-alveolar- intrapleural) Forced expiration: expiration is passive- due to elastic recoil, inspiration is active- muscles expense, expiration becomes active to empty lungs more completely & fast. To produce active expiration, muscles to further reduce volume of thoracic cavity & lungs. Further reduced in volume, recoil even smaller, intra- alveolar pressure increases further. Pressure difference b/t intra-alveolar & atmosphere is greater than passive.
