The circulatory system acts as the transport system for the body. It brings oxygen to tissues and carries carbon dioxide away. Nutrients are picked up from the digestive system and delivered throughout the body, while waste products are carried away so that certain organs may remove them. The circulatory system consists of the heart and blood vessels and includes arteries, veins, and capillaries.

Blood is the transport medium that is pumped throughout the body. It is a liquid tissue that consists of plasma and formed elements (red blood cells, white blood cells, and platelets). It is important for the medical assistant to have an understanding of this system in order to effectively perform electrocardiograms, phlebotomy, and blood tests.