Development of human lung

The development of human lung arises from the laryngotracheal groove.

The larynx, trachea, bronchi and lungs begin to form during the fourth week of embryonic development. At this time, the respiratory diverticulum (lung bud) appears ventrally to the caudal portion of the foregut. The location of the diverticulum along the gut tube is directed by various signals from the surrounding mesenchyme, including fibroblast growth factors. As the lung bud grows, its distal end enlarges to form the tracheal bud. At the same time the future trachea separates from the foregut through the formation of tracheoesophageal ridges, which fuse to form the tracheoesophageal septum.

The tracheal bud divides into two primary bronchial buds. During the fifth week of development, the bronchial buds enlarge to form right and left main bronchi. These continue to develop into secondary and tertiary bronchi.

Phases
The maturation of the lungs occurs in several phases: