Lung Development
DRUGS Stuff
Embryonic Stage (Weeks 4-7)
- Lung bud forms from the foregut.
- Trachea and primary bronchi develop.
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Compaction
- This occurs around the 8-cell stage
Pseudoglandular stage (Weeks 5–17)
- Branching of the airways forms terminal bronchioles
- No respiratory bronchioles or alveoli yet, so gas exchange is not possible
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Compaction
- This occurs around the 8-cell stage
Canalicular stage (Weeks 16–25)
- Respiratory bronchioles and alveolar ducts begin to form.
- Pulmonary capillaries develop and approach the airspaces
- Type II pneumocytes begin producing surfactant (around 20–24 weeks)
- Limited gas exchange becomes possible toward the end of this stage.
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Compaction
- This occurs around the 8-cell stage
Saccular (Terminal sac) stage (Weeks 24–38)
- Terminal sacs (primitive alveoli) develop.
- Surfactant production increases significantly
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Blood-air barrier thins, making gas exchange more efficient.
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Compaction
- This occurs around the 8-cell stage
Alveolar stage (Week 36 to ~8 years after birth)
- Mature alveoli form and continue multiplying after birth
- Most alveolar development occurs in the first 2–3 years of life, with maturation continuing until about 8 years.
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Compaction
- This occurs around the 8-cell stage
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