Think about how your body reacts if you start exercising. How do
the nervous, muscular, circulatory, and respiratory systems respond to
an increased oxygen demand?

The primary purpose of the cardiorespiratory system is to deliver adequate amounts of oxygen and remove waste from body tissues .  The purpose of cardiovascular regulation is maintaining adequate blood flow to all body tissues.  In addition, the circulatory system transports nutrients and aids in temperature regulation.  During exercise, the demand for oxygen to the muscles is 15 to 25 times greater than at rest.  The heart cannot accomplish this by itself, and does not work in isolation.  The respiratory system and the circulatory system function together as a “coupled unit” delivering the body’s oxygen and nutrients and taking away carbon dioxide and wastes to maintain homeostasis.

c. heat from the poles back down towards the equator.