The cardiovascular system is made of three systems that work together: the heart, the lungs, and the arteries, veins, coronary and portal vessels. All of these systems are responsible for the flow of blood, nutrients, oxygen and other gases, and hormones to and from cells, states Live Science.
The cardiovascular system, also called the circulatory system, moves blood to parts of the body where it can be oxygenated and where waste can be disposed. The newly oxygenated blood is then brought to the tissues of the body. Blood flows through the liver and kidneys, where waste is removed and then brought back to the lungs for fresh oxygen. This process of blood flow continues over and over.
Humans and mammals have four-chambered hearts, which ensures highly oxygenated blood is moved quickly and efficiently to the organs of the body, About.com states. The upper chambers of the heart, called the atria, receive blood entering the heart and pump it to the ventricles, which are the lower heart chambers. Atria are thin-walled while ventricles are thick-walled and contain more cardiac muscle than the atria. The additional muscle in the ventricles enables a more powerful pump that can push blood through a longer trip around the body.