PHGY 214 Lecture Notes - Lecture 3: Intercostal Muscle, Thoracic Cavity, Alveolar Pressure
12 May 2016
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Document Summary
Dynamics of flow: provide appropriate pressures at the following sites during a quiet expiration: mouth, alveoli, pleural space, and intermediate locations along the airway from alveoli to mouth. The pressure at the mouth is always 0 because it is equal to barometric pressure: at frc, when the diaphragm is relaxed. The alveolar pressure equals atmospheric pressure because there is no flow. The pleural pressure is -5 and lung pressure if +5, thus alveolar pressure is 0. The lung and chest wall pressures are at equal opposite pressures: during inspiration. Pleural pressure decreases because inspiratory muscles contract (diaphragm) A pressure gradient is established from the atmosphere to the alveoli, resulting in inspiratory flow: inspiration ends. When contraction of inspiratory muscles decrease, this allows the lung recoil pressure to catch up and equal pleural pressure. Alveolar pressure equals atmospheric pressure and flow stops: expiration starts.
