Age | Development period | Morphology and physiology | Sex differences in morphology, maturation, and physiology | |||
---|---|---|---|---|---|---|
Prenatal1-150 | ||||||
1–5 weeks | Embryonic33 | Morphology: Lung bud formation24 33 | ||||
6 to ∼15 weeks | Pseudoglandular33 | Morphology: Differentiation of airways; airway branching pattern complete by 16 weeks24; airways smooth muscle appears in trachea and starts to contract spontaneously38 | ||||
Ciliated goblet cells appear at ∼12 weeks15 38 | ||||||
16 to ∼26 weeks | Canalicular33 | Morphology: Vascularisation occurs: acini develop24; Clara cells appear by 26th week15 24 38; fetal respiration begins to influence lung development41 44 45 | Morphology: No sex differences in relationship of lung growth to somatic growth40 | |||
Maturation: Mouth movements in female more advanced than male fetus34 | ||||||
26 to ∼36 weeks | Saccular33 | Morphology: Alveoli first appear at 30 weeks and are uniformly present at 36 weeks; air space wall thickness declines rapidly after 28 weeks15 38 |
Morphology: See above40 Maturation: See above: also female fetus approximately 1.5 weeks ahead of male in lung phospholipid profiles which reflect surfactant production and maturation44 46 | |||
Rapid increase in lung volume40 | ||||||
Perinatal and postnatal | ||||||
36–40 weeks | Morphology: Alveolar multiplication occurs24 | Morphology: See above under 16 to ∼26 weeks40 | ||||
As gestation advances bronchial smooth muscle increases relative to size of airway38 | Maturation: More advanced in female than male lungs: see above under 16 to ∼26 and 26 to ∼36 weeks | |||||
Physiology: Female lungs have lower specific airway resistance than male lungs39 | ||||||
Birth to ∼1 week | Morphology: Proportion of goblet to ciliated cells increases.38 Rapid alveolar multiplication continues.33 Proportion of goblet to ciliated cells increases rapidly38 Physiology: Neonates have proportionately larger airways relative to lung volume (FRC),27 higher size corrected forced expiratory flow rates40 41 43 and lower specific airway resistance than older infants39 |
Morphology: Female lungs smaller than male lungs, may have fewer respiratory bronchioles24
Maturation: More advanced in female than male lungs,44 46 premature female lungs less at risk for RDS44 and transcient tachypnoea of the newborn47 than male lungs and more responsive to hormone accelerators of surfactant production44 Physiology: As above under 36–40 weeks39 | ||||
1 to ∼52 weeks |
Morphology: Formation of single capillary network occurs and alveolar multiplication continues,33 growth more or less linear with age at least up to age 224
Physiology: Airway resistance increases rapidly to adult levels in the first year of life39 |
Morphology: See above under birth to 1 week15
24
Maturation: Female lungs more responsive than male lungs to hormones44 Physiology: See above under 36–40 weeks,39 female infants also have higher absolute as well as size corrected forced expiratory flow rates than male infants40 |
Compiled from references 15, 24, 27, 33, 34, 38–41, 44–46.
↵1-150 Prenatal age expressed as weeks after conception.