What is the defense mechanism that helps expel mucus build-up and foreign substances from the respiratory system?

Coughing serves as a crucial defense mechanism in the respiratory system, designed specifically to clear mucus build-up and expel foreign substances, such as dust or pathogens, from the airways. When irritants are detected in the respiratory tract, the body initiates a strong, forceful expiration through the mouth, which helps to regulate airflow and rapidly remove unwanted debris from the lungs and trachea. This reflex is vital for maintaining clear air passages, ensuring that the respiratory system can function optimally.

While sneezing also plays a role in expelling irritants, it primarily targets the nasal passages and upper respiratory system, making coughing the more effective mechanism for clearing deeper sections of the respiratory tract. Yawning and swallowing do not serve the purpose of expelling mucus or foreign matter; instead, yawning is related to ventilation and oxygen intake, while swallowing is mainly a mechanism for moving food from the mouth to the stomach. Therefore, coughing is the correct answer, as it directly contributes to maintaining respiratory health by clearing the airways.