SP-A, SP-B, and SP-C in surfactant subtypes around birth: reexamination of alveolar life cycle of surfactant

Surfactant protein (SP) phospholipids SP-A, SP-B and SP-C are secreted by lamellar vessels in the fetus, with new subtypes developing as the breathing of the fetus starts. Degradation of alveolar surfactant into a remnant type having a SP-A containing lavage fluid occurs during breathing. The turn-over rate of SP phospholipids during breathing is more than that of phosphatidylcholine.