Table 4 Stages and events during lung development in humans and mice

Embryonic

4-7 weeks

9-14 days

Septation of trachea from oesophagus

Lung bud forms two main bronchi and individual lobes

Supporting structures are formed including bronchial cartilage and smooth muscle

Pseudoglandular

5-17 weeks

14-16.5 days

Branching morphogenesis begins

Proximal airway epithelial and mesenchymal differentiation occurs

Canalicular

16-26 weeks

16.5-17.5 days

Further branching

Vascularisation and angiogenesis occurs along the airway

Rapid increase in capillary numbers

Respiratory bronchioles and alveolar ducts form

Type II alveolar epithelial cells differentiate

Saccular

24-36 weeks

17.5 days to postnatal day 5

Type I alveolar epithelial cells differentiate

Type II alveolar epithelial cells maturation

Air sacs are developed

Lymphatic network develops

Surfactant begins to be produced

Initial stage of primary septation for formation of alveoli occurs

Alveolar

36 weeks to childhood

Postnatal day 5-30

Secondary septation produces alveoli

Increasing levels of surfactant produced

Majority of gas exchange surface is formed