Which of the following is an example of a respiratory system defense?

• A. Antibody production in response to pathogens
• B. Viscosity of mucus and cilia in the bronchi
• C. Inflammatory markers in the bloodstream
• D. Enzyme action in the digestive system

Answer: (B)

The viscosity of mucus and cilia in the bronchi is a fundamental defense mechanism of the respiratory system. Mucus serves as a protective barrier that traps inhaled particles, including dust, pathogens, and allergens. The cilia, tiny hair-like structures lining the respiratory tract, work in concert with the mucus. They beat in a coordinated fashion to move the mucus upwards towards the throat, where it can be swallowed or expelled. This process, often referred to as the mucociliary escalator, is crucial in maintaining lung health by preventing the accumulation of harmful substances and infections in the airways.

Other options represent defense mechanisms within different systems or biological processes. Antibody production pertains to the immune system's response to pathogens, not specific to the respiratory system. Inflammatory markers in the bloodstream relate to systemic responses to injury or infection rather than directly addressing respiratory defense. Enzyme action in the digestive system is part of the digestive process, which does not directly relate to protecting the respiratory system.