THE CIRCULATORY SYSTEM AND THE HEART
Large organisms need a transport system to move materials around the body.
Humans have a circulatory system. It consists of the heart, blood vessels and the blood. The heart is a muscular organ that pumps blood around the body. The right pump forces deoxygenated blood to the lungs where it picks up oxygen and loses carbon dioxide. The blood then returns to the heart and and is pumped to the rest of the body by the left pump.
The heart has four chambers - the left and right atria and the left and right ventricles. The atria receive deoxygenated blood from the vena cava on the left side and they receive oxygenated blood from the pulmonary vein on the left. The atria contract and force the blood into the lower chambers - the ventricles. When the ventricles contract they force blood through the pulmonary artery on the right side and the aorta on the left side. Valves in the heart prevent blood from flowing in the wrong direction. The heart muscle is supplied with oxygenated blood via the coronary arteries.
KEEPING THE BLOOD FLOWING
Blood flows around the body in three types of blood vessel: the arteries, the veins and the capillaries.
Arteries always carry blood away from the heart. They have thick walls containing muscle and elastic tissue and a narrow lumen. This is because the blood has to be transported under a high pressure.
Veins always carry blood back towards…