alveolarization

Alveolarization is the developmental process by which alveoli, the small air sacs responsible for gas exchange, are formed and increased in number within the lungs. In humans, this process begins during late fetal life and continues after birth through early childhood, significantly expanding the alveolar surface area and the lung’s capacity for oxygen transfer.

During alveolarization, secondary septa form within preexisting air spaces, subdividing larger airspaces into numerous smaller alveoli. This secondary septation increases the alveolar surface area rather than merely enlarging existing airways. The resulting architecture resembles a dense honeycomb that improves gas exchange efficiency and supports growth with body size.

Alveologenesis is driven by interactions among epithelial cells, mesenchyme, fibroblasts, and the pulmonary capillary network. Mechanical stretch from breathing and surfactant function contribute to septation, while molecular signals regulate elastin deposition, smooth muscle and fibroblast activity, and vascular remodeling.

Disruptions in alveolarization are implicated in neonatal lung diseases such as bronchopulmonary dysplasia (BPD), particularly in premature infants exposed to oxygen and mechanical ventilation. Such disruption yields simplified alveolar structures with fewer, larger alveoli, reduced surface area, and impaired gas exchange, which can influence long-term respiratory function.

Histology shows reduced septation with enlarged airspaces; imaging may reveal decreased alveolar development and interstitial remodeling in affected lungs. Research continues to explore regulators of alveologenesis and potential therapies to promote alveolar formation in at-risk populations.