Getting Air to the Lungs a. Vital capacity is maximum volume of air that can be moved in and out during a single breath. Vital capacity is sum of tidal, inspiratory reserve and expiratory reserve volumes. In emphysema , residual volume builds up and is no longer useful for gas exchange, reducing vital capacity. Inspiration Precedes Expiration a. Air passes from atmosphere through pharynx to alveoli.
Lungs lie within a sealed-off thoracic cavity.
The intrapleural pressure is less than atmospheric pressure by about 4 mm Hg. Due to greater atmospheric pressure outside, air rushes in. Expiration Is Usually Passive a. When respiratory center stops sending signals, diaphragm relaxes and returns to its original dome shape. Rib cage moves down and inward.