What common respiratory defense mechanism is active when foreign particles enter the body?

The common respiratory defense mechanism that is particularly effective when foreign particles enter the body involves cilia. Cilia are microscopic hair-like structures lining the respiratory tract that help move mucus, along with trapped particles, out of the airways. This mechanism is critical for maintaining healthy lungs and preventing respiratory infections, as it ensures that inhaled contaminants do not settle in the lungs and are expelled from the body.

While nasal hairs also play a role in filtering larger particles from the air before they reach the lungs, their function is somewhat limited compared to cilia. Cilia operate continuously and in a coordinated manner to push mucus and debris upwards toward the throat, where it can be swallowed or expelled. In contrast, macrophages are specialized immune cells that ingest foreign particles but are part of a different defensive response that occurs once particles have bypassed initial defenses. This highlights the importance of cilia as the first line of defense in the respiratory system.