What are the primary functions of the respiratory system?

The primary functions of the respiratory system include the exchange of oxygen and carbon dioxide, which is essential for maintaining the body's metabolic processes. This function occurs in the alveoli of the lungs, where oxygen from inhaled air diffuses into the bloodstream, and carbon dioxide, a waste product of cellular respiration, is expelled from the blood into the lungs to be exhaled. This gas exchange is vital for sustaining life, as oxygen is necessary for cellular processes and sustaining energy levels in the body.

In contrast, the other options pertain to functions associated with different systems in the body. The production of hormones and enzymes is primarily a function of the endocrine system and digestive system, while the circulation of blood is the responsibility of the cardiovascular system. Filtering and digesting food relates to the digestive system. Thus, the respiratory system is specifically dedicated to the crucial role of gas exchange, making it the correct choice in this scenario.