Final answer:
Respiratory bronchioles are lined with pseudostratified ciliated columnar epithelium, which contains goblet cells that produce mucus for trapping debris and pathogens. Cilia present on these epithelial cells help in transporting the mucus towards the throat.
Step-by-step explanation:
The respiratory bronchioles are an integral part of the lower respiratory system and are involved in the delicate process of gas exchange. They are not lined with keratinized stratified squamous epithelium, simple cuboidal epithelium, stratified columnar epithelium, or nonkeratinized stratified squamous epithelium. Instead, the correct answer to what lines the respiratory bronchioles is option C. pseudostratified ciliated columnar epithelium.
Pseudostratified ciliated columnar epithelium features a single layer of cells differing in heights that give the appearance of stratification, as every cell's base touches the basement membrane, a configuration well-elucidated in Figure 22.5 and elsewhere. This type of epithelium also features goblet cells, which produce mucus to trap debris and pathogens. The presence of cilia aids in the movement of this mucus towards the throat, where it can be swallowed and expelled from the body. The primary role of this epithelium is to protect the respiratory system from invasive microorganisms and to facilitate the gas exchange process.