UPPER RESPIRATORY TRACT EPITHELIUM AND ITS PROTECTIVE FUNCTION

Abstract

This abstract examines in detail the morphological, histological, and immunobiological characteristics of the upper respiratory tract epithelium, which provides multilevel protection of the body against inhaled pathogens and harmful environmental factors. The upper respiratory tract (nose, nasopharynx, larynx, and initial segments of the trachea) is lined mainly by pseudostratified ciliated columnar epithelium with pronounced structural specialization. It includes ciliated cells, goblet cells, basal stem cells, brush cells, endocrine cells, and areas of stratified squamous epithelium in regions exposed to increased mechanical stress.

The epithelium performs barrier, transport, sensory, immune, and secretory functions, enabling constant interaction between the external environment and intrinsic mechanisms of homeostasis. The study emphasizes that the key protective mechanism of the epithelial lining is mucociliary clearance, formed by coordinated ciliary activity and the tracheobronchial secretion layer consisting of two components: the gel layer (mucus) and the sol layer (periciliary fluid). Histologically, this apparatus is supported by specialized epithelial cells secreting the mucins MUC5AC and MUC5B, as well as ion channel regulation that ensures proper mucus hydration.

The upper respiratory tract epithelium is considered an active immune organ. It contains innate immune receptors (TLR, NOD pathways), secretory IgA, β-defensins, lysozyme, lactoferrin, and other antimicrobial factors. Special attention is given to interactions between the epithelium and local immune system cells — dendritic cells, macrophages, lymphoid follicles, and MALT components (NALT, BALT), which contribute to the formation of local adaptive immunity.

A separate focus is placed on the regenerative potential of the epithelium. Basal cells with stem-cell properties provide continuous renewal of the epithelial lining and physiological plasticity, including the ability for metaplasia and restoration of the ciliated surface after injury. The study examines morphofunctional changes in the epithelium under the influence of risk factors: viral infections (especially respiratory viruses), bacterial toxins, air pollutants, tobacco smoke, allergens, and xenobiotics. Particular attention is given to the toxic effects of organophosphate compounds, including chlorpyrifos, which disrupt mucociliary transport, damage cilia, increase epithelial permeability, intensify inflammatory responses, and induce tissue remodeling.

The abstract emphasizes that the upper respiratory tract epithelium is a highly specialized system integrating mechanical (cilia), chemical (mucins, enzymes), immunological (secretory IgA, antimicrobial peptides), and cellular (dendritic cells, lymphocytes) protective mechanisms. The complexity and synergy of these mechanisms ensure effective filtration, inactivation, and removal of foreign particles, maintaining sterility in the lower respiratory tract. The results highlight the importance of studying epithelial morphological changes under harmful exposures and the need to develop strategies for preventing mucociliary dysfunction and epithelial barrier impairment.