The main function of the respiratory system in animals is to facilitate the exchange of gases, primarily oxygen and carbon dioxide. Through the process of respiration, oxygen is inhaled into the lungs, where it diffuses into the bloodstream and is transported to cells for metabolic processes. Meanwhile, carbon dioxide—a byproduct of cellular metabolism—is expelled from the body when exhaling. This gas exchange is critical for maintaining homeostasis, providing energy for cellular functions, and sustaining life. The respiratory system is closely linked to other systems, including the circulatory system.