lungesurfaktant

Lung surfactant, also known as pulmonary surfactant, is a complex mixture of lipids and proteins that lines the alveolar surface to reduce surface tension at the air–liquid interface. It is produced and secreted by type II pneumocytes in the lung epithelium and is essential for normal breathing mechanics.

The predominant components are lipids, especially dipalmitoylphosphatidylcholine (DPPC), along with other phospholipids and cholesterol. Surfactant proteins, designated SP-A, SP-B, SP-C, and SP-D, play roles in film spreading, stabilization, and immune defense. Together these constituents form a monolayer that rapidly adsorbs to the expanding surface during inflation and re-spreads during deflation.

Functionally, surfactant lowers alveolar surface tension, preventing collapse at end expiration (atelectasis) and reducing the work of breathing. It also helps regulate alveolar fluid balance and contributes to innate immune defense through SP-A and SP-D, which participate in pathogen recognition and clearance.

Surfactant homeostasis involves synthesis by type II cells, secretion into the alveolar lining, and turnover with recycling of components. Alveolar macrophages participate in its degradation and clearance. Disruptions in production or function can impair gas exchange.

Clinically, insufficient or dysfunctional surfactant causes respiratory distress in neonates, most notably in preterm infants lacking mature type II cells. Surfactant replacement therapy, using animal-derived or synthetic preparations, improves oxygenation and outcomes. Surfactant dysfunction is also implicated in acute respiratory distress syndrome and other lung injuries, where therapeutic strategies aim to restore surface-tension–reducing activity.