Which of the following systems is NOT involved in the breathing process?

The circulatory system is not directly involved in the breathing process, which specifically refers to the mechanics and exchange of gases in the respiratory system. Breathing, or pulmonary ventilation, involves the physical movement of air into and out of the lungs. This process allows for external respiration, where oxygen is exchanged for carbon dioxide in the alveoli of the lungs. Internal respiration refers to the exchange of gases at the cellular level, where oxygen is utilized by cells and carbon dioxide is produced as a waste product. While the circulatory system is essential for transporting these gases throughout the body, it does not engage in the act of breathing itself. Thus, the other systems are integral to the definitions directly associated with the process of breathing, highlighting that the circulatory system serves a supportive and transportive role rather than a direct role in breathing mechanics.