Which of the following is a protective mechanism in the respiratory system?

• A. Cilia
• B. Bradycardia
• C. Peripheral vasodilation
• D. Increased tidal volume

Answer: (A)

Cilia are hair-like structures that line the airways of the respiratory system. Their primary role is to trap and expel foreign particles, pathogens, and mucus from the respiratory tract. When air inhaled into the lungs carries dust, allergens, or microbes, cilia help by moving in a coordinated wave-like motion to push these unwanted substances up toward the throat, where they can be swallowed or coughed out. This mechanism is crucial in preventing infections and maintaining clear air passages, making cilia an essential protective feature of the respiratory system.

Bradycardia refers to a slower-than-normal heart rate, which does not serve a protective function in the respiratory system. Peripheral vasodilation, the widening of blood vessels in the periphery, primarily affects blood flow and temperature regulation rather than directly aiding respiratory health. Increased tidal volume relates to the volume of air inhaled or exhaled during normal breathing; while it can enhance gas exchange, it is not a protective mechanism in the context of preventing respiratory issues. Thus, cilia stand out as a vital protective mechanism against respiratory threats.