At what stage do alveoli (air sacs) fully form?

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From the Research

Alveoli continue to form and mature throughout childhood and adolescence, with the process of alveolarization extending beyond early childhood, as evidenced by the most recent study in 2022 1. The development of alveoli is a complex and prolonged process that starts in the womb and continues after birth.

  • The formation of new alveolar septa from preexisting ones was previously thought to cease due to the reduction of a double- to a single-layered capillaries network inside the alveolar septa, but recent studies have challenged this view 2.
  • New evidence suggests that alveolarization continues throughout adolescence, with the number of alveoli increasing by approximately 1.94-fold between 7 and 21 years of age 3.
  • The process of alveolarization is characterized by the formation of new septa, which can occur at any time and at any location inside the lung parenchyma, and is influenced by the development of the alveolar capillary network 1.
  • The exact timing and mechanisms of alveolar development are still not fully understood, but it is clear that alveolarization is a critical process that continues throughout childhood and adolescence, with important implications for lung function and disease susceptibility 3, 1.
  • The most recent study in 2022 provides quantitative data about the internal lung structure, showing that the number of elements composing the alveolar capillary network expands massively during the first two postnatal weeks and exceeds the formation of alveoli, with the thinning of the alveolar septa during further development suggesting a reduction of the capillary network during alveolarization 1.

References

Research

Differential temporal development of alveoli and the alveolar capillary network in the postnatal rat lung.

American journal of physiology. Lung cellular and molecular physiology, 2022

Research

Evidence and structural mechanism for late lung alveolarization.

American journal of physiology. Lung cellular and molecular physiology, 2008

Research

Alveolarization continues during childhood and adolescence: new evidence from helium-3 magnetic resonance.

American journal of respiratory and critical care medicine, 2012

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