Final answer:
The respiratory tract is lined by a mucosa with pseudostratified columnar epithelia, cilia, and mucus-secreting goblet cells. This structure facilitates the trapping of particles and pathogens and their removal by the mucociliary escalator effect. Structural changes occur along the tract to adapt to various functions.
Step-by-step explanation:
The respiratory tract is lined by a mucosa, which exhibits structural changes along its length to serve different functions. This mucosa features pseudostratified columnar epithelia with cilia and goblet cells. The columnar epithelial cells exist in one layer but give the appearance of being stratified due to the varying levels at which their nuclei are situated. Goblet cells, interspersed between the columnar epithelial cells, secrete mucus. This mucus serves to trap particles and pathogens. Additionally, the cilia present on the free surface of the epithelial cells beat rhythmically to propel the mucus and captured debris in an upward direction, away from the lungs in a mechanism called the mucociliary escalator effect. As we move from the nose through the bronchi, there is a decline in the number of goblet cells and a change in the type of epithelium present, which is adapted to perform other functions such as sensing odors or metabolizing airborne carcinogens. The defensive role of the mucosa is pivotal in the body's ability to prevent inhaled microorganisms from reaching the lower respiratory tract.