Phases of lung development

1.      Embryonic : 

                                           i.     In utero

                                         ii.     3- 5 weeks

                                        iii.     Formation of primitive lung tissue and vascular connection

                                        iv.     Trachea and bronchi differentiation

2.     Pseudo glandular:

                                           i.     In utero

                                         ii.     05-16 weeks

                                        iii.     Formation of conducting air way

                                        iv.     Immature neural network

                                          v.     Appearance of type-II pneumocyte

3.      Canalicular:

                                           i.     In utero

                                         ii.     17-26 weeks

                                        iii.     First gas exchanging acini and pulmonary capillaries are forming.

                                        iv.      Vascular and lymphatic system develop alongside the bronchial tree.

                                          v.     Appearance of type-I pneumocyte.

                                        vi.     Beginning of surfactant production

4.     Saccular :

                                           i.     In utero

                                         ii.     27-36 weeks

                                        iii.     Alveolar saccule formation

                                        iv.     Maturation of surfactant system

                                          v.     Breathing effort begin.

                                        vi.     ECM formation

5.      Alveolar :

                                           i.     At birth

                                         ii.     37 weeks to 3+ years

                                        iii.     Mature alveolar formation

                                        iv.     Reduction of interstitial tissue.

                                          v.     Proliferation and expansion of capillary, nerve and gas exchange area.

                                        vi.     ECM formation.