![]() ![]() Alveolar - weeks 32-8 years - terminal sacs -> adults alveoli (due to 2 degree septation) - in utero breathing occurs via aspiration and explusion of amniotic fluid -> increase in vascular resistance through gestation - at birth, fluid gets replaced with air, leading to a decrease in pulmonary vascular resistance Note: - at birth -> 20-70 m alveoli - by 8 years -> 300-400 m alveoli Saccular - weeks 26-birth - alveolar ducts -> terminal sacs - terminal sacs are separated by 1 degree of septae - pneumocytes develop 5. ![]() Canalicular - weeks 16-26 - terminal bronchioles -> respiratory bronchioles -> alveolar ducts - surrounded by prominent capillary network - respiration capable at 25 weeks 4. ![]() Pseudoglandular - weeks 5-16 - endodermal tubules -> terminal bronchioles -> alveolar ducts - surrounded by modest capillary network - at this point, respiration is impossible and this is incompatible with life 3. Embryonic - weeks 4-7 - lung bud -> trachea -> mainstem bronchi -> secondary (lobar) bronchi -> tertiary (segmental) bronchi - note: errors at this stage can lead to TE fistula 2. initial development includes development of the lung bud from the distal end of the respiratory diverticulum during week 4 - the lung bud divides into two bronchial buds that branch off into bronchi 1. How many stages does lung development occur in? - 5: embryonic, pseudoglandular, canalicular, saccular and alveolar Name the stages and describe the important structures derived during each stage. ![]()
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