Respiratory System Development

The respiratory system consists of various epithelial tissues including the trachea, bronchi, lungs, and associated vasculature and muscle. Respiration serves the vital function of gas exchange via the close association of blood vessels with the branched airway system of the lungs. Overall, lung development is driven by intercellular signaling events, epithelial to mesenchymal transition, and tissue remodeling via the action of proteases. During embryogenesis, FGF signaling from the adjacent cardiac mesoderm is required for pulmonary cell fate specification of the endoderm. Lung development then occurs through a stepwise progression that includes: budding from the foregut endoderm, division and branching of the bronchi (regulated by TGF-beta signaling), vascularization during the canalicular stage, terminal cell differentiation during the saccular period, and alveoli formation. Finally, the lung undergoes a series of postnatal remodeling events such as programmed mesodermal cell death, which thins the vascular-alveolar interface and permits efficient gas exchange.