What are the main structures of the respiratory system?

The main structures of the respiratory system include the nasal cavity, trachea, lungs, and bronchus. The nasal cavity serves as the entry point for air, filtering and humidifying it before it moves deeper into the respiratory tract. The trachea is a tube that connects the throat to the lungs, allowing air to pass through. Once in the lungs, air is further divided into smaller passages, including the bronchi and bronchioles, facilitating gas exchange within the alveoli—tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged.

Understanding the primary components of the respiratory system is crucial, as they work together to ensure proper breathing and gas exchange, which is vital for sustaining life. Each of these structures plays a specific role in the process of respiration, contributing to the overall function of this system. The other options listed pertain to different systems in the body, such as the circulatory system, urinary system, and digestive system, which do not involve the respiratory process directly.