What is is the purpose of a circulaorty system?

The circulatory system allows for the transport of vital substances (chemicals, blood gases, etc. throughout the body for availability to cells). One of its primary functions in this respect is to pump oxygenated blood from the lungs into the heart, out to the body for cells to use for oxidative phosphorylation and energy generation, and then pump carbon dioxide-rich blood back through the heart and to the lungs, where carbon dioxide can be exchanged for oxygen again.