Functional morphology of the mucociliary transport system in the bronchi of rats during postnatal ontogeny

BACKGROUND: Age-related changes in the mucociliary transport system (MCTS) of the airways may play a significant role in the pathogenesis of respiratory diseases. However, studies examining the structural and functional parameters of the bronchial epithelium throughout postnatal ontogeny, using uniform methodological approaches, are lacking. AIM: To study the age-related patterns of postnatal morphogenesis of the mucociliary transport system in the bronchi of rats based on a structural and functional analysis of its elements

METHODS: The respiratory epithelium of the main, lobar, and segmental bronchi from 76 Wistar rats at ages from 1 day to 26 months was examined using methods such as assessment of ciliary activity, light and electron microscopy, immunocytochemistry, morphometry.

RESULTS: The bronchial tree of newborn rats is lined with a simple epithelium predominantly composed of undifferentiated cells (59-62%) and a small number of ciliated cells (21-26%). Differentiation of MCTS elements is most pronounced during the first month and develops asynchronously: in the first two weeks the number of ciliated cells increases by 2.2-2.7 times; the formation of the goblet cell occurs between days 14 and 30. The frequency of ciliary beating is highest in newborn animals (25-25.9 Hz), decreasing to 14.9-18.6 Hz in one-month-old rats and stabilizing at 13.2-16.2 Hz for all subsequent time points. The completion of the typical structure of the respiratory epithelium occurs during puberty: starting from 3 months and continuing through the reproductive period (6-14 months), its main quantitative structural and functional characteristics stabilize. In aging and old animals, the content of ciliated and goblet cells reaches its peak values, while the motility of the ciliary apparatus is preserved. Concurrently, a decrease in the number of proliferating cells, an increase in hypertrophied ciliated cells, and the development of ultrastructural signs of epithelial cell damage are recorded.

CONCLUSION: Postnatal morphogenesis of the MCTS in the bronchi continues throughout the animal's life, with histogenetic processes being most pronounced during the first month of life. After the definitive structure of the epithelial layer is established, subsequent age-related transformations aim to maintain a stable level of mucociliary clearance throughout the animals' later life.