Importance of this System

In your body, the circulatory system does a very important job. This provides oxygen and vital nutrients to all cells in the arteries around the body and retains in veins the waste products and carbon dioxide. Without this system, you would not be able to function and the blood flowing around your body would not be able to travel. In fact, it would be impossible for you to breathe without this system 

https://www.khanacademy.org/science/high-school-biology/hs-human-body-systems/hs-the-circulatory-and-respiratory-systems/a/hs-the-circulatory-system-review