The circulatory system is made up of the heart, blood vessels and blood. Functions of the blood: transport, heat regulation, protection against disease and protection against blood loss from injury. Blood is made up of plasma and blood cells. Plasma transports nutrients, chemicals, waste, carbon dioxide and heat around the body. There are three types of blood cells. Red blood cells contain haemoglobin which bonds to oxygen. Red blood cells carry oxygen around the body. White blood cells defend the body against disease. Platelets help to clot the blood.
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There are three types of blood vessels: arteries, veins and capillaries. Arteries carry blood away from the heart. Veins carry blood towards the heart. Capillaries link arteries and veins.
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Arteries have thick walls to withstand blood flowing at high pressure. Veins have valves to prevent blood at low pressure flowing backwards. Capillaries have very thin walls to allow substances to diffuse through them easily. The heart is the pump of the circulatory system. It is composed of cardiac muscle which never tires. The heart has four chambers: right atrium, right ventricle, left atrium and left ventricle. The left ventricle has a thick wall because it pumps oxygen-rich blood all around the body. The right side of the heart receives carbon dioxide-rich blood from the body and pumps it to the nearby lungs. Double circulation consists of a circuit between the heart and lungs and another circuit between the heart and the rest of the body. The average resting pulse rate is 70 beats per minute. The circulatory system interacts with the digestive system to transport food molecules around the body. The circulatory system interacts with the respiratory system to transport gases around the body. Heart disease is prevented by regular exercise, a healthy diet, not drinking too much alcohol, not smoking and avoiding stress.
