Columnar epithelial tissue in the respiratory tract has hair-like projections to faciliatate movement of mucus up and out of the lungs.
These hair-like projections are called: A fibers B cillia C flagella D keratin
The correct answer and explanation is:
The correct answer is B. cilia.
Cilia are hair-like projections found on the surface of certain epithelial cells, including those in the respiratory tract. These projections play an essential role in maintaining respiratory health by helping to move mucus, trapped particles, and pathogens out of the lungs. The respiratory epithelium is lined with these cilia, which beat in a coordinated manner, generating a sweeping motion that propels mucus toward the throat. This process is known as the mucociliary escalator.
The mucus produced in the respiratory tract serves as a barrier, trapping inhaled dust, microbes, and other foreign particles. Once trapped, the cilia work together to move the mucus toward the pharynx, where it can either be swallowed or expelled from the body through coughing. This mechanism helps keep the airways clear and prevents the buildup of harmful substances in the lungs.
Cilia are made up of microtubules and are connected to a motor protein system that powers their movement. This movement is essential not only in the respiratory system but also in other systems of the body, such as the reproductive and digestive systems, where cilia help transport eggs and facilitate the movement of fluids.
In contrast, A. fibers are structural components, C. flagella are similar to cilia but are typically longer and found on sperm cells, and D. keratin is a protein that forms the structure of hair, nails, and the outer layer of skin, none of which are directly involved in mucus movement in the respiratory tract. Therefore, the correct term for the hair-like projections facilitating mucus movement in the lungs is cilia.