ABSTRACT
Pulmonary surfactant is a lipoprotein substance that is synthesized and secreted by the pulmonary alveolar type II cell. 1 Surfactant is stored within the type II cell in lamellar bodies, organelles that are released by exocytosis into the alveolar lumen (Figure 1). The secreted surfactant then lines the alveolus and, by reducing the surface tension of the aqueous-lining layer, prevents the collapse of alveoli during the expiratory phase of respiration. Surfactant deficiency in the newborn can lead to the development of respiratory distress syndrome (RDS), the leading cause of death in premature newborns in the U.S. 2 Another disease, adult respiratory distress syndrome (ARDS), may also be caused by deficiency or inactivation of pulmonary surfactant. 3 Recently, in several clinical trials, it has been shown that surfactant replacement can be an effective therapy for diseases characterized by surfactant deficiency or inactivity. 4 , 5 Further progress in the treatment of these diseases will depend on a better understanding of the synthesis, secretion, and metabolism of pulmonary surfactant. 6 An electron micrograph of a human fetal lung type II cell. Type II cells are characterized by organelles called lamellar bodies (LB) in which surfactant is stored. The apical surfaces of type II cells are covered with microvilli (MV). Coated pits (CP) and multivesicular bodies (MVB) are frequently observed within type II cells. The nucleus (N), rough endoplasmic reticulum (RER), Golgi apparatus (G), and mitochondria (M) are also labeled. (Original magnification × 22,800.) (Adapted from Snyder, J. M., Johnston, J. M., and Mendelson, C. R., <italic>Cell Tissue Res</italic>., 220, 17, 1981. With permission.) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780367812812/dde770a6-6408-4307-97e1-b30f5a049440/content/fig107_1.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>
