<Dl> <Dd> P = 2 γ r (\ displaystyle P = (\ frac (2 \ gamma) (r))) </Dd> </Dl> <Dd> P = 2 γ r (\ displaystyle P = (\ frac (2 \ gamma) (r))) </Dd> <P> Compliance is the ability of lungs and thorax to expand . Lung compliance is defined as the volume change per unit of pressure change across the lung . Measurements of lung volume obtained during the controlled inflation / deflation of a normal lung show that the volumes obtained during deflation exceed those during inflation, at a given pressure . This difference in inflation and deflation volumes at a given pressure is called hysteresis and is due to the air - water surface tension that occurs at the beginning of inflation . However, surfactant decreases the alveolar surface tension, as seen in cases of premature infants suffering from infant respiratory distress syndrome . The normal surface tension for water is 70 dyn / cm (70 mN / m) and in the lungs it is 25 dyn / cm (25 mN / m); however, at the end of the expiration, compressed surfactant phospholipid molecules decrease the surface tension to very low, near - zero levels . Pulmonary surfactant thus greatly reduces surface tension, increasing compliance allowing the lung to inflate much more easily, thereby reducing the work of breathing . It reduces the pressure difference needed to allow the lung to inflate . The lung's compliance decreases and ventilation decreases when lung tissue becomes diseased and fibrotic . </P> <P> As the alveoli increase in size, the surfactant becomes more spread out over the surface of the liquid . This increases surface tension effectively slowing the rate of expansion of the alveoli . This also helps all alveoli in the lungs expand at the same rate, as one that expands more quickly will experience a large rise in surface tension slowing its rate of expansion . It also means the rate of shrinking is more regular, as if one reduces in size more quickly the surface tension will reduce more, so other alveoli can contract more easily than it can . Surfactant reduces surface tension more readily when the alveoli are smaller because the surfactant is more concentrated . </P>

How does surfactant reduce surface tension in the lungs
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