Final answer:
Metaplasia is the process where cells like ciliated columnar cells change to become stratified squamous cells, often as a protective adaptation in response to chronic irritation. Columnar cells are typical of the respiratory tract and may change to stratified squamous epithelium for additional protection.
Step-by-step explanation:
The process by which one type of cell changes to another type, such as when ciliated columnar cells change to form stratified squamous cells, is called metaplasia. This biological process involves the reprogramming of stem cells that are present in the tissue. Metaplasia is often a response to chronic irritation and inflammation, where the tissues adapt to better protect themselves against the stress or damage. An example of this can be seen in the respiratory tract, which typically is lined with pseudostratified columnar epithelium; in some cases of chronic irritation, this can change to a more protective stratified squamous epithelium. Columnar cells line the respiratory tract and have a single layer of tall and closely packed cells. These cells can be ciliated and help move mucus in the respiratory tract. However, when they transform into stratified squamous cells, the tissue gains multiple layers of cells for added protection. This type of epithelium is found in areas subjected to abrasion, such as the skin and lining of the mouth. Stratified squamous epithelium specifically refers to layers of flat cells stacked on top of each other, and this kind of tissue is named based on the shape of the top, or apical, layer of cells. In some parts of the body, such as the skin, the squamous cells may be keratinized for additional protection, while in moist surfaces like the mouth, they are non-keratinized.