Pulmonary surfactant and lung fluid balance

Key Points: Pulmonary surfactant is a unique mixture of phospholipids and specific apoproteins covering the entire internal surface of the lung. Surfactant components are synthesised in alveolar type II cells, secreted into the epithelial lining layer and metabolised either by reuptake into type II cell or by phagocytosis and degradation by alveolar macrophages. Besides reduction of surface tension at the air-liquid interface, its major biophysical funcion, pulmonary surfactant possesses immunomodulatory effects and plays a role in the innate immune system. In the alveolar compartment pulmonary surfactant is important for lung fluid balance because of its high surface pressure. The principal forces responsible for transcapillary fluid movement from the vascular to the interstitial compartment are best described by Starling's equation of fluid exchange.