Heart, Blood, and Circulation
Adequate blood circulation is essential for life. The blood is kept in constant cir- culation by the pumping action of the heart, which sends blood to the lungs to pick up oxygen, and then pumps it to the rest of the body. The blood is pushed through a system of vessels, which branch repeatedly into increasingly smaller and thinner vessels, bringing life-sustaining blood to cells throughout the body.
The heart is a muscular organ about the size and shape of a ﬁst and consists of two side-by-side pumps.The veins carry used, oxygen-depleted blood to the right side of the heart, which pumps it to the lungs for a fresh supply of oxygen.The oxygenated blood returns to the left side of the heart, which pumps it through the aorta.The aorta directs the fresh blood to a system of arteries, which carry it to tissues throughout the body.The veins return the used, oxygen-depleted blood to the heart, starting the process again.
The Circulatory System
The circulatory system is a network of blood vessels that branch out from the heart into smaller and smaller channels.The heart and circulatory system work as a single system to transport blood to and from all the cells of the body.