Surfactant lipid synthesis and exocytosis. Simplified scheme of intracellular pathways leading to de novo synthesis of DPPC and its routing to lamellar bodies, from where it will be released into the alveolar lumen, where it will be used, recycled and degraded. For the synthesis, CDP-choline and diacylglycerol are coupled to form PC. A large proportion of PC is remodeled to render DPPC. Surfactant is stored in lamellar bodies until secretion to the alveolar lumen, where it organizes in bilayers and monolayers (see text for further detail). The surfactant life cycle is completed by its recycling by T2C or degradation by AM. T1C: type 1 cell; T2C: type 2 cell, AM: alveolar macrophage; LB: lamellar body; SP: surfactant protein; PC: phosphatidylcholine; DPPC: dipalmitoylphosphatidylcholine; CCTα: CTP:phosphocholine cytidylyltransferase alpha; PLA2: phospholipase A2; LPCAT1: lysophosphatidylcholine acyltransferase 1.