The muscle fibres grow into the part where the atheroma creating a plaque which grows and narrows the lumen of the artery.
If the plaque grows too large it tears the endothelium of the artery and a thrombus forms at the site of the tear.
If the thrombus detaches and breaks loose it is called an embolus, the embolus will travel down the artery until it is trapped. It completely blocks the artery which is called an embolism and if it occurs in a blood vessel to the brain, heart muscle or the lungs it can be fatal.
An aneurysm happens when the build up of pressure in an artery causes it to swell up and weaken as it is narrowing. The swollen blood vessels press on the surrounding tissues, the aneurysms often burst which causes severe blood lost if this happens in the brain it is called a stroke.
Many factors can affect the development of coronary heart disease some of them can be controlled and therefore prevented but others you cannot control. You cannot control these factors:
- Age. The older you are the more risk you have of developing coronary heart disease.
- Gender. Males are at greater risk of getting coronary heart disease as oestrogen protects women against it.
- Heredity. Some families are at greater risk of high blood pressure, which increases the risk of developing coronary heart disease.
- Diabetes. Diabetics are at a greater risk of getting coronary heart disease, as the heart needs to work harder and this puts a strain on it.
There are also many controllable factors, which we need to avoid,
Lack of physical activity can lead to coronary heart disease, when you do aerobic exercise (continuous endurance exercise) the heart enlarges as the muscles become bigger and the size of the chambers in the heart increase. This increases the stroke volume and at rest, an untrained heart will have to beat faster than a trained heart as it has a smaller stroke volume. This is also because the activity of the parasympathetic nerves increases; these nerves release acetylcholine, which slows down the heart rate. As a trained heart has a slower resting heart rate, the heart does not need to work as hard so it requires less oxygen. The coronary blood supply is less in a trained heart so the risk of getting coronary heart disease is decreased. Exercise also helps to use up excess body fat and if not taken regularly it can lead to obesity. Being over weight or obese increases the risk of getting coronary heart disease as the heart has to work harder to do things e.g. it would take more effort to walk up the stairs if you were overweight as you have more fat to carry. This means that a greater strain is put on the heart. Diet is also important as high blood cholesterol is directly linked with coronary heart disease. Cholesterol is a type of lipid and when it is carried in the blood it is combined with proteins forming lipoproteins. Low-density lipoproteins contain high levels of cholesterol, which increases the risk of atherosclerosis and therefore coronary heart disease. Arteriosclerosis (the hardening of the arteries) and atherosclerosis (the narrowing of the arteries) can cause long-term hypertension, which is where the blood pressure is high and it puts a strain on the heart. High blood pressure can lead to the arteries thickening its muscle layer, which means that the lumen narrows and the blood pressure is increasing. The blood pressure gets so high that it causes damage to the endothelium, which increases the risk of an atheroma forming. Hypertension can also be caused by obesity, too much salt in the diet, excess alcohol intake and smoking.
People that smoke cigarettes are about 4 times more likely to develop coronary heart disease than people that do not. Heart attacks are also more likely to be fatal for people that smoke. People that smoke pipes or cigars are twice as likely to develop coronary heart disease as people that do not smoke.
The carbon monoxide from tobacco smoke reduces the amount of oxygen that the red blood cells can carry which increases the risk of damage to the endothelial cells in the arteries. Tobacco smoke contains a substance called nicotine, which is a vasoconstrictor. Vasoconstrictors narrow the arteries which also means that the blood pressure is increased and there are more possibilities for the arteries to become blocked by an embolus. Tobacco smoke is also known to increase the levels of cholesterol in the blood. The number of platelets in the blood are also increased they become more sticky, this stimulates the formation of blood clots.
There are many ways in which coronary heart disease can be treated, drugs such as beta-blockers and calcium antagonists can be used to lower blood pressure, decrease the heart rate, reduce the retention of fluids and decrease the cholesterol in the blood.
If the drug treatments do not work then a coronary by-pass operation may be necessary. This is where a blood vessel from the leg is used to replace the dead vessel on the heart. The by-pass carries blood from the aorta to a part of the coronary artery past the blockage.
There is also a new less invasive method, which involves stretching coronary arteries by inserting a deflated balloon into the femoral artery in the leg and positioning it in the narrowed coronary artery. Once in position the balloon is inflated.
Bibliography
Internet
Books
A complete guide to sport and PE written by Kevin Wesson, Nesta Wiggins, Graham Thompson and Sue Hartigan
A new introduction to human biology written by, Bill Indge, Martin Rowland and Margret Baker.
Leaflets
Written by BUPA called how to prevent heart disease
