Development of Lung

March 6, 2013 | By | Reply More

Development of Lung

  1. Pseudoglandular period
    1. Comprises weeks 5-16 when conducting system is formed as far as terminal bronchiole
    2. Birth during this period is incompatible with life.
  2. Canalicular period
    1. Comprises weeks 16-26 when terminal bronchioles give rise to respiratory bronchioles, each of which divides into alveolar ducts, and respiratory vasculature forms
    2. Some terminal sacs (primitive alveoli) develop toward end of period, so some infants born late in canalicular period may survive with intensive care

      Some infants born at 22-25 weeks survive with intensive care but often suffer lifelong disability.

  3. Terminal sac period
    • Comprises week 26-birth when more terminal sacs develop and pulmonary surfactant is produced by type II alveolar cells (pneumocytes)

      Pulmonary surfactant produced by type II alveolar cells reduces surface tension to prevent alveolar collapse.

  4. Alveolar period
    • Comprises week 32 of gestation through age of 8 years when alveoli form and mature; boundary between terminal sac and alveolar period open to interpretation


Surfactant reduces surface tension to allow inflation of alveoli. Neonatal respiratory distress syndrome (hyaline membrane disease) results from deficient surfactant production by type II alveolar cells in premature infants. Glucocorticoid treatment in at-risk pregnancies speeds up lung development and surfactant production. Treatment with artificial surfactant reduces neonatal mortality.

Maternal glucocorticoid treatment may prevent neonatal respiratory distress syndrome.

Category: Anatomy

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