Lung Embryology:
- LRT (lower respiratory tract) arises from laryngotracheal diverticulum.
- Wk 24 – resp bronchi form, respiration is possible.
- Wk 29 – type II secrete surfactant (reaches adequate levels 2 wks before birth).
- Trachea – C-shaped cartilage.
- Left bronchus longer, narrower, greater angle; bronchi have circum rings of crtlg; pseudostrat colum epi, Goblet, neuosecr, basal, brush cells.
- Epi à lamina propria à submuc à cartilage.
- Bronchioles – no cartilage, submucosal glands.
1) Membranous – smooth muscle wall; ciliated columnar cells + Clara cells.
2) Respiratory – alveolar ducts, alveoli budding from wals; no musc. wall; cuboidal cells +/- cilia.