The circulatory system is the name given to the heart, blood vessels and blood which transport oxygen and nutrients to all parts of the body as well as carry away waste products. The heart, a hollow but muscular organ, is the central organ in the circulatory system. Located in the chest slightly to the left of centre, the average adult heart is the size of a person's clenched fist. As a person exercises, the heart will beat faster to supply the body with more blood and oxygen. One-way valves control the flow of blood through these four chambers.
Smaller arteries branch off from the aorta and carry blood to organs and tissue.
The time between the beginning of one heartbeat to the beginning of the next is called the cardiac cycle . The heart muscle contracts when these electrical impulses run across it. If the natural pacemaker ceases to function properly, an artificial pacemaker can be used to regulate the heartbeat. Blood vessels Blood vessels are the series of arteries and veins which carry blood through the body. Arteries carry oxygen-rich blood from the heart to the various parts of the body.