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The postnatal development and growth of the human lung. II. Morphology
Insights
Human lung development involves rapid alveolar formation and septal maturation in the first 1.5 years. This study details the structural remodeling from infancy to early childhood, crucial for understanding lung growth.
Area of Science:
- Pulmonology
- Developmental Biology
- Histology
Background:
- Postnatal lung development is a complex process involving structural changes.
- Understanding human lung growth is essential for pediatric respiratory health.
Purpose of the Study:
- To investigate the morphological changes in human lung development from 26 days to 64 months.
- To compare postnatal human lung development with adult lungs and other species.
Main Methods:
- Light microscopy
- Scanning electron microscopy
- Transmission electron microscopy
Main Results:
- Significant structural remodeling occurs within the first 1.5 postnatal years, characterized by alveolar formation and septal restructuring.
- Immature septa with double capillary networks mature into adult structures with single capillary networks by 1.5 years.
- Lung development progresses rapidly, with significant maturation by 6 months.
Conclusions:
- Postnatal human lung development comprises two overlapping stages: alveolar stage (late fetal to 1-1.5 years) and microvascular maturation stage (birth to 2-3 years).
- The lung undergoes substantial remodeling during infancy, transitioning from rapid alveolarization to microvascular maturation.
Abstract:
The morphology of postnatal human lung development and growth has been investigated by light and by scanning and transmission electron microscopy in seven children dying from non-respiratory causes and aged between 26 days and 64 months. The findings are compared with those of adult human lungs and are discussed in relation to the postnatal lung development in other species, particularly rodents. Within the first 1 1/2 postnatal years lung parenchyma undergoes a substantial structural remodeling due to bulk alveolar formation and to the restructuring of septal morphology. At one month alveolar formation appears to be well under way: The human lung is comparable then to a rat lung aged one week. In the parenchyma, numerous short and blunt tissue ridges, so-called secondary septa, subdivide the peripheral airspaces into an increasing number of still very shallow alveoli. The parenchymal septa present during and after alveolization are immature: they contain a double capillary network with a central, highly cellular sheet of connective tissue. The septal maturation sets in a few months after birth and consists of a reduction in the interstitial tissue mass and a complex process of capillary remodeling. Both alveolization and parenchymal maturation progress rapidly: by 6 months the lung has taken a big step towards maturity. By 1 1/2 years most septa show the adult structure where a single capillary network interwoven with connective tissue strands stabilizes the interalveolar wall. After the septal restructuring, lung development is considered complete, and the lung enters a period of normal growth that lasts until adulthood. From our observations we conclude that postnatal human lung development is made of two overlapping stages: (a) the alveolar stage, which starts in late fetal life and lasts to about 1-1 1/2 years, and (b) a stage of microvascular maturation, thought to extend from the first months after birth to the age of 2-3 years.