- external intercostal muscles contract while internal intercostal muscles relaxes
- ribs swing upward and outward (sternum moved up and further away from the backbone increases dorsoventral diameter of thorax)*
- diaphragm contracts and flattens thus enlarging thoracic cavity
- increase thoracic cavity results in a decreased thoracic cavity pressure
- expansion of lungs reduces air pressure in the alveoli
- alveolar air is at a lower pressure than that of atmospheric air outside the body
- air rushes into the lungs until pressure at both sides is equal.
- gaseous exchange between alveoli and blood
- oxygen dissolves in the moisture lining in alveolar walls.
- diffusion of oxygen into blood and carbon dioxide into alveolar cavity.
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