Which of the following structures is NOT part of the respiratory system?

The stomach is not a part of the respiratory system. The respiratory system is primarily responsible for the exchange of gases, particularly oxygen and carbon dioxide, between the body and the environment. It includes structures designed specifically for this function, such as the bronchi, alveoli, and lungs.

The bronchi are the large air passages that branch from the trachea into the lungs, directing airflow. The alveoli are tiny air sacs where gas exchange occurs, allowing oxygen to enter the blood while carbon dioxide is expelled. The lungs house these structures and are the primary organs of respiration. In contrast, the stomach is part of the digestive system, responsible for breaking down food, and does not play a role in breathing or gas exchange. This distinction underscores the importance of anatomical classification in understanding body systems and their functions.