[Pulmonary surfactant system]

The lung surfactant system (LSS) has a complex morphological and biochemical structure. LSS contains two components: cellular and non-cellular. The cellular component comprises three types of alveolar epithelium cells (type I, II, and II pneumocytes), alveolar macrophages (AM) and Clara bronchiolar cells. The non-cellular component consists of alveolar surfactant (AS), hypo(epi)phase and alveolar epithelium cell glycocalix. AS represents phospholipids, proteins and carbohydrates mono-molecular layer. AM lamellar bodies (LB) and tubular myelin (TM) are disposed in the hypophase. LB and TM represent the depot-forms of lung surfactant (LS). Lung surfactant (LS) has a complex biochemical structure and comprise the following components: phospholipids, neutral lipids, glycolipids, surfactant-specific proteins, plasmaproteins, enzymes, carbohydrates and aminoacids. LS is synthesized in type II pneumocytes and Clara cells. LS catabolism is mainly effected by AM. The LSS has a fundamental role in the physiological functions of lungs. Through its antiatelectatic and antioedematic functions, LSS sustains the basic physiological functions of lungs--alveolar ventilation and gas diffusion through the alveolar-capillary wall. Besides this, LSS performs several protecting functions--antioxidant defense, non-specific defense mechanisms, immunodulatory action, cytotoxicity agents metabolism and others. The injury of the structure and functions of LSS is an important pathogenic mechanism in the pathogenesis of different lung diseases. Practically, a pathological process in lungs, which is not related to changes in LSS structure and functions, does not exist. Recently developed surfactant replacement therapy with natural and synthetic surfactants has an important place in the therapy of several lung diseases.