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

The kidney is not a part of the respiratory system; it is part of the excretory system. The primary function of the kidneys is to filter blood, remove waste products, and regulate fluid balance in the body. In contrast, the nose, trachea, and bronchi are all integral components of the respiratory system, which is responsible for taking in oxygen and expelling carbon dioxide.

The nose serves as the entry point for air, filtering and humidifying it before it travels to the trachea. The trachea, or windpipe, is a tube that connects the throat (pharynx) with the bronchi, which further branch off into the lungs. The bronchi direct air into each lung. This organized structure plays a critical role in ensuring that the respiratory process functions effectively, highlighting the specific functions of each component within the respiratory system while distinguishing them from unrelated systems like the excretory system.