Lung Maturation
_Pseudoglandular (5-17 weeks)
§No
gas exchange zones
§Lung
resembles an exocrine gland
_Canalicular (17-25 weeks)
§Terminal
bronchioles enlarge and branch 2-3 respiratory bronchioles then 3-6 alveolar ducts. Terminal sacs begin to form
_VAscularized – caudal slower than cranial
_Terminal sac (25 weeks to 34 weeks) – blood flow
and surfactant
§Epithelium
thins to become type I like
§Capillaries
grow in
§Blood
air barrier forms
_Type I and type II cells
§Surfactant
reduces surface tension allowing expansion.
_Alveolar period (late fetal to childhood)
§Surfactant
§Gas
exchange
§Pulmonary
vs systemic circulation
§Alveoli
mature from age 3-8. Numbers increase from 50 million at birth and 300 million at age 8 (adult number)