Lung surfactant

Residing at the interface of the body, the lung is a uniquely vulnerable organ optimized for gas exchange, having a very thin, delicate epithelium, abundant blood flow, and a vast surface area. Lung surfactant is a surface active material composed of both lipids and proteins that is produced by alveolar type II pneumocytes that provides a stable, low surface tension for the lung, thereby preventing alveolar collapse at low transpulmonary pressure. Surfactant is a secretory product, composed of lipids and proteins. Phosphatidylcholine and phosphatidylglycerol are the major lipid constituents and SP-A, SP-B, SP-C, SP-D are four types of surfactant associated proteins. The lipid and protein components are synthesized separately and are packaged into the lamellar bodies in the AT-II cells. Lamellar bodies are the main organelle for the synthesis and metabolism of surfactants. The synthesis, secretion and recycling of the surfactant lipids and proteins is regulated by complex genetic and metabolic mechanisms. Alterations in surfactant homeostasis or biophysical properties can result in surfactant insufficiency which may be responsible for diseases like respiratory distress syndrome, lung proteinosis, interstitial lung diseases and chronic lung disease.