Which of the following organs is not part of the respiratory system?

The heart is not part of the respiratory system; it plays a vital role in the circulatory system instead. While the heart works closely with the lungs to facilitate the exchange of oxygen and carbon dioxide in the blood, it does not participate directly in the process of respiration. The primary components of the respiratory system are designed to facilitate gas exchange, including the lungs, trachea, and pharynx. The lungs are the primary site for gas exchange, the trachea acts as the windpipe, allowing air to enter the lungs, and the pharynx serves as a pathway for air to move from the nose and mouth to the trachea. Understanding these distinctions is key to grasping the overall anatomy and physiology of the body's systems.