DSF Lung Dev

Question 1

Embryonic phase

Answer 1

weeks 3-8
bifurcation of R & L bronchial buds
pattern of branching regulated by surrounding visceral/splanchnic mesoderm
(development of airway through the bronchopulmonary segments - each of which is supplied by a segmental bronchus, artery (pulmonary) & intersegmental vein)

Question 2

Pseudoglandular phase

Answer 2

weeks 5-17
*No alveoli at this stage!
characterized by branching of airway to level of terminal bronchioles (all of conducting airway)

Question 3

Canalicular phase

Answer 3

weeks 16-26
*Most clinically relevant phase!
Formation of respiratory bronchioles, w/ invasion of capillaries into the mesenchyme - forming the air-blood barrier!
chief characteristic: alteration of epithelium - thinning of respiratory epithelium to simple squamous

Question 4

Saccular Phase

Answer 4

weeks 24-birth
formation of alveolar sacs
established air-blood barrier (surrounding capillaries multiply)
ensures viability of fetus @ 24-26 wks, w. surfactant detectable in blood

Question 5

Alveolar Phase

Answer 5

week 36 to 18 months postpartum
formation of alveoli - they increase in # & size
alveolar maturation occurs after birth