(1) Coronary heart disease is a disease of the arteries supplying blood to the muscle forming the walls of the heart. The blockage of a coronary artery is called a coronary thrombosis or heart attack, causing extreme and gripping chest pains. If a coronary artery is blocked, part of the heart muscle does not receive any blood. The muscle cells receive no oxygen, they cannot respire and therefore they die. The size of the heart attack depends upon the size and position of the coronary artery blocked. If a small branch of an artery is blocked, only a small amount of muscle dies causing a small heart attack. If a large artery is blocked, the whole heart may stop contracting, resulting in a cardiac arrest. (1))
(1) Atherosclerosis is the main cause of CHD. This is the progressive blocking of arteries with atheroma. These are deposits of cholesterol and fibrous tissue which narrow the arteries, reducing blood flow and making the artery walls less elastic, and therefore roughening their inner surface. There are a number of factors that can affect Atherosclerosis.((4) Lack of physical inactivity is a common risk factor. 7 out of 10 adults in the UK do not take enough regular physical activity. (4)) Physical activity also raises HDL cholesterol levels which with regular physical activity lowers the damaging LDL levels. Regular exercise helps to prevent blood clotting by providing sufficient blood flow to remove and stop the build-up of atheroma, therefore preventing coronary thrombosis. (4))
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Preventing the build-up of atheroma can be prevented by physical exercise as this raises the amount of high-density lipoprotein cholesterol in our arteries. However, it is the fact that excess cholesterol is present in our arteries that results in a dangerous amount of atheroma forming in the coronary artery and this excess come from our diet. ((1) Some cholesterol is essential for our bodies to function as it are needed in cell membranes, however, the level of cholesterol entering our bodies through diet is a major factor affecting coronary heart disease. The level of LDL cholesterol in the blood tends to rise, and HDL falls, with the number of saturated fats and ((5) triglycerides in a diet. (1+5)) ((4) Atheroma develops when LDL cholesterol is oxidised and is taken up by cells in the coronary artery walls where the narrowing process begins eventually resulting in a blockage and therefore coronary thrombosis. (4))
A major factor that affects coronary heart disease is high blood pressure and this can be linked to a lack of physical exercise. Being overweight and having a lack of rhythmic exercise can increase blood pressure. This also links to diet as eating too much salt or drinking too much alcohol can also increase blood pressure. ((4) High blood pressure can cause the heart to become abnormally large and less efficient resulting in left ventricular hypertrophy. ((2) This is a condition where the cardiac muscle responds to increased resistance in the circulation by becoming enlarged.
However, with time, the many fibres of the hypertrophied heart muscle become thickened and shortened, and consequently less able to relax. ((2) The outcome of this process is a heart that is less able to meet the output demands of normal circulation. Hypertension makes the myocardium work harder and therefore more difficult to relax and go through the normal cycle of contraction and relaxation. The myocardium results in having differential amounts of collagen resulting in increased stiffness. (2)) ((3) Therefore there is an impaired diastolic relaxation, but also heightened vulnerability to ischemic events. The end result is decreased cardiac output, and the inability to meet the circulatory needs of the body, resulting in heart failure.
Coronary heart disease is far more common in smokers than in non-smokers. Nicotine which is present in cigarettes ((1) diffuses into the blood and quickly increases blood pressure, heart rate and narrows blood vessels. It also raises the level of fat in the blood. These effects combine to increase the risk of Atherosclerosis as they increase the likelihood of narrowing the coronary artery and forming a blockage. Both nicotine and carbon monoxide damage the endothelium lining the blood vessels. This makes it easier for fats and cholesterol to enter the blood vessel, therefore increasing their deposition inside the arteries. (1)) Therefore a pattern can emerge as smokers have narrowed arteries due to cholesterol and other fatty deposits causing Atherosclerosis as a result of smoking. ((1) Tobacco smoke also induces platelets to stick to the wall of the endothelium, so speeding up the formation of a blood clot. Therefore increasing the risk of coronary heart disease.
There are four main factors that I have described and that can cause coronary heart disease.
These are high cholesterol levels resulting in atheroma forming due to diet, lack of physical exercise, smoking tobacco and high blood pressure. These factors are also often related. For example, a bad diet with high cholesterol can lead to a person being overweight. Being overweight can lead to physical inactivity which then can raise blood pressure. Smoking on top of this also makes it easier for triglycerides and cholesterol to enter the blood vessel. Therefore if a person has all of these factors then the chances of coronary heart disease are much higher and one factor can also cause another factor to emerge such as high blood pressure due to being physically inactive therefore again increasing the chances of coronary heart disease.
1) AS level Biology. Bradfield, Dodds, Taylor. Longman.2001. p289-295
2) Gwathmey JK, Briggs GM, Allen PD. Heart Failure: Basic Science and Clinical Aspects New York: Marcel Dekker, 1983.
5) New Scientist Journal. Issue 2506 of New Scientist magazine, 02 July 2005, page 23. Eric Kvaalen Paris, France
6) AQA Biology specification A…Bill Indge
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