Heart Disease

The cardiovascular system (comprising of the heart, arteries and veins) is essential for keeping homeostasis balanced throughout the body.

The heart works as a pump to push blood containing oxygen and nutrients through the extensive network of arteries and arterioles to replenish organs, tissues and respiring cells, once replenishment has taken place waste products and carbon dioxide are removed and taken back to the heart in the blood stream through veins and venules to be redirected through the pulmonary circulation back to the lungs to be deoxygenised (see appendix 1).

The heart also needs to be replenished with oxygen rich blood to survive; blood is supplied to the heart by the coronary circulation (see appendix 2).

Just like any other organ in the body, the heart and surrounding vessels are susceptible to disease. One of these many diseases is Coronary Heart Disease.

Coronary heart disease is the most common cause of premature death in the United Kingdom. On average every year 110.000 people die from heart related diseases, whilst 300.000 people have heart attacks and more than 1.4 million suffer from angina, (British Heart Foundation 2001). CHD is caused by a number of “risk factors” (risk factors are issues that can contribute to a disease). Risk factors associated with CHD are high blood pressure (hypertension), cigarette smoking, alcohol, physical inactivity, obesity (being overweight), and high blood cholesterol.

As fatty foods are consumed and digestion initiates, saturated fats from the digested food is broken down by the liver to produce cholesterol. Passing into the bloodstream the cholesterol combines with proteins to create “lipoproteins”. Lipoproteins are used for transporting numerous types of lipids to and from the cells. Lipoproteins are divided into two categories, high density lipoproteins (HDL) and low density lipoproteins (LDL). HDL’s remove excess cholesterol from the cells and transports it to the liver to be destroyed, whereas LDL’s are responsible for supplying cells with cholesterol. The cells in the body have LDL receptors attached to them. Once inside the cell the LDL is broken down and cholesterol is released to fulfil the cells requirements. When the cell has adequate cholesterol to function a negative feedback prevents the cell from making new LDL receptors. Unfortunately CHD can also be a genetic disease, thought to be caused by a mutation in the apolipoprotein B (main protein in the low density lipoprotein group). The mutation causes insufficient production of receptors and therefore high levels of cholesterol are released increasing the susceptibility to CHD. With the combination of high levels of LDL and raised levels of homocysteine (an amino acid, building blocks that make up protein) derived from methionine another amino acid which is found in eggs, milk and meat atherosclerosis occurs (see appendix 3).

Atherosclerosis is caused by a build-up of cholesterol and fatty substances on the inner wall of the artery, beginning as fatty streaks which gradually develop to form lumps known as plaques (see appendix 4). Raised homocysteine levels damage the lining of the artery whilst plaques assist the walls of the artery to thicken and harden therefore the lumen of the artery narrows. This results in myocardial ischemia (poor blood flow to the heart) and the oxygen needs being suspended (hypoxia). As the hearts requests for oxygen surpass the amount available the heart omits warning signs in the form of tightening and pain in the chest, sometimes extending to the upper extremities, lumber area and abdomen, this is clinically referred to as stable angina. In extreme cases of atherosclerosis the plaques in the misshapen coronary artery affect blood flow resulting in the development of blood clots (thrombus) When a thrombus occurs (see appendix 5), it blocks the artery triggering an attack of unstable angina, if the heart continues to be starved of oxygen for more than a few minutes the heart muscle begins to die resulting in myocardial infarction (heart attack). Myocardial infarction can contribute to total starvation of the heart resulting in congestive heart failure and inventively death.

Some heart attacks can be looked upon as warning signs and that a change in lifestyle is required. There are many prescribed medications available to reduce the risks of heart failure, for example; aspirin is used to reduce the stickiness of the platelets therefore reducing the risk of blood clots (thrombus). Diuretics (which target the kidneys to increase