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Describe how the structure of arteries, veins and capillaries enables them to fulfil their functions - Discuss the possible links between lifestyle and coronary heart disease.

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UNIT B ASSIGNMENT- ESSAY. Describe how the structure of arteries, veins and capillaries enables them to fulfil their functions. Discuss the possible links between lifestyle and coronary heart disease. The human heart is a muscular pump which has four chambers, two atria which receive blood from the veins and two ventricles which pump blood away from the heart. The heart is responsible for pumping the blood to every cell in the body. It is also responsible for pumping blood to the lungs, where the blood gives up carbon dioxide and takes on oxygen. This is known as double circulation as the blood passes through the heart twice on its journey around the body, the blood is returned to the heart after passing through the lungs, before being pumped over the body tissues to supply nutrients and oxygen. This helps to sustain a high blood pressure which allows rapid circulation. (See diagram 1.1) Blood is pumped around the body by the heart through vessels. There are three types of vessels, arteries, veins and capillaries. These aren't just tubes through which blood flows and aren't anatomically the same. Their structure is related to the function they perform, the diameter of arteries and veins slowly reduces the further away from the heart they are. ...read more.


As they don't constrict they have valves throughout to stop the blood pooling or flowing back towards the legs under the influence of gravity. Veins are usually surrounded by skeletal muscle which contracts as a result of movement and pushes the blood along the vein in one direction. Semi-lunar valves stop the blood flowing backwards, they work by allowing the blood to flow past but as it flows backwards it opens the flaps of tissue that make the valve and it fills with blood which closes the lumen and stops blood going back past the valve.(see diagram 1.3) Capillaries are the smallest of the vessels and it is in these that exchanges between the blood and body cells take place. This is possible because the capillary walls are very thin and permeable allowing small soluble molecules to pass through. (See diagram 1.2) When the blood flowing through them is seen through a microscope the cells are seen to pass through one at a time. Capillary beds, which are like a spider's web in the liver, allow the blood to give up waste products which are then disposed of in urine. They also allow the transfer of carbon dioxide and oxygen from the blood and enable white blood cells to leave the blood and fight against foreign bodies. ...read more.


A balanced diet that doesn't contain high amounts of saturated fat would reduce the chances of heart disease. Exercise is very important in reducing the chances of heart disease. The heart being a muscle gets stronger with exercise; repeated exercise will increase the amount of heart muscle and the size of the heart chambers. In return the heart will pump a greater volume of blood per beat and so beat fewer times. Although global trends show the same increase in heart disease the levels around the world differ. In developing countries where the economic situation isn't good, the food that is available is rarely deep fried or contains high levels of fat. The people get more exercise as their jobs are more physical, as a result they burn off excess fat. In a country such as the U.K where food is in plentiful supply and often contains high levels of fat i.e. chocolate, crisps, chips etc, most people are employed in jobs that involve much less physical activity and so don't burn off fat as easily. As a result of these different lifestyles heart disease is much higher in developed parts of the world. WORD COUNT 1,329 SOURCES Collins advanced science biology Mike Boyle, Kathryn Senior Bio Fact sheet number 37 January 1999 www.accessexcellence.org The heart and the circulatory system Roger E Phillips Understanding biology for advanced level Glenn and Susan Toole University of Bath Science Biology Martin Rowland ...read more.

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