In thoracic cavity development in infants, when are the lungs viable outside the uterus?

• A. 5 weeks
• B. 10 weeks
• C. 15 weeks
• D. 20 weeks

Answer: (D)

The ability of lungs to function outside the uterus depends on maturation of the airways and the presence of surfactant to keep the alveoli open for gas exchange. By about 20 weeks gestation the lung is in the canalicular stage with developing respiratory bronchioles and early type II pneumocytes that begin producing surfactant. This combination allows the alveolar units to inflate and sustain gas exchange at birth, especially with neonatal support. Earlier than this, the air spaces and surfactant are not sufficient for life outside the womb; later weeks see further maturation, but the earliest point at which viability can begin is around 20 weeks.