The respiratory system is responsible for breathing — taking in oxygen and expelling carbon dioxide. It includes the lungs, trachea, diaphragm, and airways. While proper oxygenation is crucial for hormone function and cellular processes, the respiratory system itself does not produce or regulate hormones. Its main role is in gas exchange, which provides the oxygen needed by every organ system to function properly, including the endocrine system. It does not release or manage hormones like insulin, cortisol, or estrogen. If you’re being asked about which system controls hormones specifically, the respiratory system is not the answer — that task belongs to the endocrine system.