Reviewing the stages of lung development on a weekly basis, you can see
how each detail of a mature lung is filled in:
| Gestational Age in Weeks |
Anatomical Description |
| 3 weeks (3 mm embryo) |
The lung structure arises as a pouch from a primitive foregut. |
| 4 weeks |
Cartilaginous rings seen in trachea. |
| 6 weeks |
Tracheobronchial tree with 18 segmental bronchi has developed. |
| 6-7 weeks (14 mm embryo) |
A series of monopodial and irregular dichotomies branching results
in 10 principle branches on the right and 8 on the left. |
| 8 weeks |
Diaphragm is formed. |
| 10 weeks |
The development of cartilage begins. |
| 12 weeks |
Mucus glands, goblet cells, and cilia are formed. |
| 16 weeks |
The bronchi formation is nearing completion and cartilage continues
to develop. |
| 20 weeks |
Differentiation of respiratory epithelium. The airways are patent
and the pulmonary vascular system begins to develop. |
| 23-24 weeks |
Surfactant production, lung parenchyma, and pulmonary circulation. |
| 24 weeks |
The bronchi show outpouching at their terminal ends and these begin
to multiply and form clusters. |
| 26 weeks |
A-C membrane may sustain extrauterine life. |
| 26-28 weeks |
Extrauterine life is now possible, although usually difficult. The
pulmonary vascular system is functional and the pulmonary structures
are nearing completion. |
| 34-36 weeks |
A-C membrane mature, alveolar number increasing. |
