Figure 3.

Overview of the stages of lung development. Lung development occurs in five stages: the embryonic (E9.5–E12.5 in mice), pseudoglandular (E12.5–E16.5), canalicular (E16.5–E17.5), saccular (E17.5–P0), and alveolarization stages (P0–P14). In the embryonic stage, two primary lung buds and a simple trachea tube arise from the diverticulum and separate from the esophagus. In the pseudoglandular stage, the highly orchestrated branching process begins to form an airway network. In the canalicular stage, conducting airways stop elongating, and distal tip cells differentiate into alveolar epithelial cells. In the saccular stage, alveolar epithelial type II cells product surfactant to prepare the organism for birth. In the alveolar stage, alveoli become mature with alveolar septum development