Pulmonary surfactant:

The presence of surfactant reduces the surface tension of the alveolar lining layer and therefore the inward pull of the alveolar wall This in turn means that the hydrostatic pressure in the interstitium around the capillaries is less negative when surfactant is present. As a result, this helps to prevent transudation of fluid from the capillaries into the interstitium or into the alveolar spaces. The other choices are incorrect: Surfactant decreases the surface tension of the alveolar lining liquid it is secreted by type II alveolar epithelial cells it is a phospholipid, and it decreases the work required to expand the lung.