The Circulatory system is one of the body's most important and makes sure blood is carried through the body as needed.A True Book: Health and the Human Body series introduces young investigative readers to the human body and what makes it work. This series includes an age appropriate (grades 3-5) introduction to curriculum-relevant subjects and a robust resource section that encourages independent study. Readers will learn all about the human body and the intricate highway of veins and arteries that make up the circulatory system.