Which of the following is NOT an organ of the respiratory system?

The kidneys are not an organ of the respiratory system; they belong to the urinary system. The primary function of the respiratory system is to facilitate gas exchange, allowing for the intake of oxygen and the expulsion of carbon dioxide. The organs involved in this system include the nasal cavities, trachea, and bronchi, which all play critical roles in breathing and air passage. The nasal cavities warm and humidify the air, the trachea serves as a conduit for air reaching the lungs, and the bronchi branch off from the trachea to distribute air into each lung. Hence, the kidneys, which are responsible for filtering blood and producing urine, clearly stand apart from these functions, making them the correct answer for the organ not associated with the respiratory system.