Final answer:
The respiratory tract is lined by mucous membranes with pseudostratified ciliated columnar epithelium and goblet cells, which form the mucociliary escalator that traps and propels pathogens out of the respiratory system.
Step-by-step explanation:
What Lines the Respiratory Tract?
The respiratory tract is lined by mucous membranes which provide a crucial defense mechanism against pathogens and particulate matter. These membranes include pseudostratified ciliated columnar epithelium with interspersed goblet cells. The goblet cells secrete a sticky mucus that traps harmful particles, and the cilia move this mucus towards the epiglottis where it is then swallowed. This action, known as the mucociliary escalator, helps to prevent inhaled microorganisms from entering the lower respiratory tract and assists with maintaining respiratory health.
Additionally, as air passages narrow down towards the alveoli, the epithelium gradually transitions from pseudostratified columnar to simple squamous epithelium, streamlining the surface for effective gas exchange. The lungs themselves are major organs of the respiratory system, facilitating gas exchange at the respiratory membranes of alveoli where blood is oxygenated.