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The Circulatory System The circulatory system is made up of the heart, the blood and the blood vessels (such as veins and arteries) Main functions of the circulatory system: • To transport substances (e.g. food, oxygen) around the body • To fight disease • To maintain constant body temperature Part of Blood Function Blood Plasma To transport food, carbon dioxide and heat around body To transport oxygen from lungs to other parts of body To fight disease Red Blood Cells White Blood Cells Platelets To clot the blood (to form a scab) Function of the heart: to pump blood around the body Difference between left and right ventricle: The left ventricle has a thicker muscular wall than the right ventricle. • This is because blood in the left ventricle has to be pumped all around the body. • The blood in the right ventricle only has to be pumped as far as the lungs. Arteries and Veins • Arteries and veins are the blood vessels that transport blood around the body. Main arteries in the body: Aorta: Carries blood away from the heart to the rest of the body. Pulmonary artery: Carries blood away from the heart to the lungs, where oxygen passes into the blood. Main veins in the body: • Vena Cava: Carries blood back into the heart from the body. • Pulmonary Vein: carries blood back into the heart from the lungs. This blood now contains oxygen. Capillaries • • Capillaries are tiny blood vessels that link arteries to veins. Capillaries have very thin walls so substances (e.g. food, oxygen) can easily pass through them. • Blood flowing through arteries is usually rich in oxygen and glucose. • When the blood flows into the capillaries, glucose and oxygen pass out of the capillaries into the cells of the body. • In the cells glucose and oxygen are converted into carbon dioxide and energy during respiration. • This CO2 and other wastes pass out of the cells and into the capillaries. • This blood then flows into the veins. This blood is no longer rich in glucose and oxygen, but is now rich in CO2 and wastes. Valves • • • • Veins carry blood at low pressure. To prevent blood flowing backwards, veins have valves. Valves can open to allow blood to pass through but close afterwards to prevent the blood going backwards. The heart also has valves to prevent the backflow of blood. Main differences between Arteries, Veins and Capillaries Arteries carry blood Away from the heart Veins carry blood into the heart Capillaries connect arteries to veins Arteries carry blood at high pressure Veins carry blood at low pressure Capillaries carry blood at medium pressure Due to the high blood pressure, arteries have thick muscular walls Due to the low blood pressure, veins have thin muscular Capillaries have very thin walls (only one cell thick) Arteries do not have valves Veins have valves, to prevent blood flowing backwards Capillaries do not have valves Most arteries carry oxygenated blood, apart from the pulmonary artery Most veins carry deoxygenated blood, apart from the pulmonary vein As blood flows through the capillaries, oxygen passes from the capillaries into the cells in the body Vein Artery Capillary Exercise and the Heart The average pulse rate for an adult at rest is 70 beats per minute (b.p.m) What causes a pulse? The pumping of blood by the heart causes changes in the blood pressure in the arteries, which causes a pulse. Experiment: Investigating the effect of exercise on the heart rate (pulse) (1) Find a pulse, for example at the wrist. (2) Count the number of beats in one minute (bpm) at rest. (3) Run on the spot for 5 minutes. (4) Count the bpm again. (5) Rest for 5 minutes and count the bpm again. Result: The bpm incareases during exercise, but goes back dowm to normal again after rest. The pulse rate increases during exercise. This is because the cells need more oxygen to release energy during respiration. After a period of rest, the pulse rate goes back to normal again. This is beacuse the cells no longer need as much oxygen to release energy. The fitter a person is, the quicker their pulse rate will return to normal after they have finished exercising. Body Temperature The normal body temperature is 37 °C. The circulatory helps to maintain this constant body temperature by transporting heat around the body. When people are ill however their body temperature often rises, as they are trying the fight the infection. Food and the Circulatory System Digested food enters the blood by passing into capillaries that surround the small intestine. The blood then transports the food to all the cells for respiration. By the end of this section, you should be able to: describe the composition and functions of blood (white blood cells, red blood cells and platelets in liquid called plasma) state the function of the heart, describe its structure identifying the four chambers explain the difference between the left and right ventricle describe the passage of blood through the heart and lungs via arteries and veins identify the pulmonary artery and vein, aorta and vena cava distinguish between arteries, veins and capillaries demonstrate the effect of exercise and rest on the pulse rate and appreciate that a balance of each promotes good health recall that the average pulse rate id 70 b.p.m, and explain why exercise results in increased pulse rates recall that the normal temperature of the human body is 37 °C and that illness may cause a change in body temperature associate the circulation of the products of digestion around the body with their absorption into the bloodstream