end expiration start expiration Transpulmonary pressures during expiration air mid expiration air Ptp

What keeps the lung inflated at end-expiration? 1.The negative Ppl

end expiration -5 0 Lungs collapse if chest is opened

What keeps the lung inflated at end-expiration? 2. Alveolar surfactant (phospholipid secreted by alveolar type II cells)

Type I Type II water type II cell type I cell alveolar space The alveolar air-water interface

Type I Type II water air Air-water interfacial tension T T Palv T Laplace: If Palv constant, Alveolar radius 1

Type I Type II water air T Alveolar surfactant decreases air-water tension T Palv T Alveolar radius 1

Lung volumes residual volume total lung capacity inspiratory volume expiration tidal volume (500 ml) functional residual capacity inspiration 3 L 6 L 1.5 L