ABSTRACT
The primary functions of the respiratory system are air conducting, olfaction, and gas exchange. The development of the mammalian respiratory system involves interaction between epithelial cells derived from a ventral outpouching of foregut endoderm and mesenchymal cells from the splanchnic mesoderm, and it begins at embryonic day 9 to 9.5 in the mouse. The conductive system includes the nasal cavity, pharynx, larynx, trachea, and bronchi, which filter, warm, and moisten air as it moves toward the gas exchange regions. The respiratory system may be divided functionally into conductive, transitional, and gas exchange regions. To providing a physical barrier and contributing to the mucociliary escalator, mucins provide specific protection to the respiratory system via influenza virus aggregation and hemagglutinin inhibition and by reducing the respiratory burst of neutrophils. Quantitative analysis of test article-related effects in the respiratory system is hampered by issues of sample bias due to the nonuniform distribution and size of cells and structures.
