Surfactant secreted by

Surfactant is produced by type II alveolar epithelial cells. Typical lamellar bodies, membrane-bound organelles containing whorls of phospholipid, are formed in these cells and secreted into the alveolar lumen by exocytosis. Tubes of lipid called tubular myelin form from the extruded bodies, and the tubular myelin, in turn, forms the phospholipid film. Following secretion, the phospholipids of surfactant line up in the alveoli with their hydrophobic fatty acid tails facing the alveolar lumen. Surface tension is inversely propoional to their concentration per unit area. The surfactant molecules move fuher apa as the alveoli enlarge during inspiration, and surface tension increases, whereas it decreases when they move closer together during expiration. Some of the protein-lipid complexes in surfactant are taken up by endocytosis in type II alveolar cells and recycled.Ref: Ganong review of medical physiology 23rd edition Page no: 597