Final answer:
Goblet cells are the mucus-producing cells that line the trachea and mainstem bronchi, which form part of the pseudostratified ciliated columnar epithelium and contribute to the mucociliary escalator mechanism.
Step-by-step explanation:
The mucus-producing cells that line the trachea and mainstem bronchi are called goblet cells. These cells are part of the pseudostratified ciliated columnar epithelium. Goblet cells secrete mucus which serves to trap debris and pathogens, thus protecting the respiratory system. The mucociliary escalator is the mechanism by which the cilia of the respiratory tract move the mucus layer and trapped particles upwards towards the throat, where they can then be swallowed.
This mucus production and transport is a primary defense mechanism of the respiratory system, preventing the invasion of pathogens and the accumulation of particulates in the lungs. The structure of the trachea and bronchi, including the C-shaped rings of cartilage, also supports and maintains the airway open, allowing for efficient air passage.