(a) Atherosclerosis

• Atherosclerosis is the accumulation of fatty material (consisting mainly of cholesterol, fibrous material and calcium) forming an atheroma or plaque beneath the endothelium.
• As the atheroma grows the artery thickens and loses its elasticity.
• The diameter of the artery becomes reduced and blood flow becomes restricted resulting in increased blood pressure.
• Atherosclerosis is the root cause of various cardio vascular diseases including angina, heart attack, stroke and peripheral vascular disease.

(b) Thrombosis

• Atheromas may rupture damaging the endothelium.
• The damage releases clotting factors that activate a cascade of reactions resulting in the conversion of the enzyme prothrombin to its active form thrombin.
• Thrombin causes molecules of the plasma protein fibrinogen to form threads of fibrin.
• The fibrin threads form a meshwork that clots the blood, seals the wound and provides a scaffold for the formation of scar tissue.
• The formation of a clot (thrombus) is referred to as thrombosis.
• In some cases a thrombus may break loose forming an embolus and travel through the bloodstream until it blocks a blood vessel.
• A thrombosis in a coronary artery may lead to a myocardial infraction (MI), commonly known as a heart attack.
• A thrombosis in an artery in the brain may lead to a stroke.
• Cells are deprived of oxygen leading to death of the tissues.

(c) Causes of peripheral vascular disorders       

• Peripheral vascular disease is narrowing of the arteries due to atherosclerosis of arteries other than those of the heart or brain.
• The arteries to the legs are most commonly affected.
• Pain is experienced in the leg muscles due to a limited supply of oxygen.
• A DVT is a blood clot that forms in a deep vein most commonly in the leg. This can break off and result in a pulmonary embolism in the lungs.

(d) Control of cholesterol levels

• Cholesterol is a type of lipid found in the cell membrane.
• It is also used to make the sex hormones — testosterone, oestrogen and progesterone.
• Cholesterol is synthesised by all cells, although 25% of total production takes place in the liver.
• A diet high in saturated fats or cholesterol causes an increase in cholesterol levels in the blood.
• Cholesterol is a component of cell membranes and a precursor for steroid synthesis.
• HDL transports excess cholesterol from the body cells to the liver for elimination.
• This prevents accumulation of cholesterol in the blood.
• LDL transports cholesterol to body cells.
• Most cells have LDL receptors that take LDL into the cell where it releases cholesterol.
• Once a cell has sufficient cholesterol a negative feedback system inhibits the synthesis of new LDL receptors and LDL circulates in the blood where it may deposit cholesterol in the arteries forming atheromas.
• A higher ratio of HDL to LDL will result in lower blood cholesterol and a reduced chance of atherosclerosis.
• Regular physical activity tends to raise HDL levels.
• Dietary changes aim to reduce the levels of total fat in the diet and to replace saturated with unsaturated fats.
• Drugs such as statins reduce blood cholesterol by inhibiting the synthesis of cholesterol by liver cells.