The respiratory system, and the lungs in particular, are the product of a set of complex developmental interactions between two distinct tissues, the endodermally derived epithelium and the mesoderm. Each tissue contributes to lung development by regulation of the spatial and temporal pattern of gene expression. Growth factors (GF) play a major role in the development of the lung. Five stages are described for the lung and respiratory system development.

In the embryonic stage (four to seven weeks), an endodermal respiratory diverticulum (laryngotracheal groove) develops from the ventral surface of the foregut, caudally to the last pharyngeal pouch. During the initial stages of lung laryngotracheal groove development, and the subsequent formation of the bronchial tree, fibroblast growth factor-10 (FGF-10) stimulates the proliferation and activation of cells that express FGF receptors. This is a critical step in development. The laryngotracheal groove grows, and...