when you run, you begin to breathe heavier and faster. Your heart beats more quickly, bringing more oxygen to your cells. Which organ systems are working together here?

Answer: Circulatory and respiratory

During running, the rate of breathing increases, because of increase in demand of oxygen by the body. The process of running affects the function of the lungs which is a part of the respiratory system. The heart is labored to pump out blood fastly, so as to transfer oxygenated blood all over the body. The heat energy is liberated in this process, which results in the release of sweat by the skin. The sweat gets evaporated by the external air, which keeps the body cool. Hence, circulatory and respiratory systems works together during running.