heart disease

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  • Heart disease
    • Heart disease kills more people in the UK than any other disease. Almost half of heart disease deaths are from coronary arteries.
      • Atheroma
        • Atheroma is a fatty deposit that forms within the wall of an artery. It begins as fatty streaks that are accumulations of white blood cells that have taken up low density lipoproteins.
          • These streaks enlarge to form an irregular patch or atheromatous plaque which commonly occurs in larger arteries and are made up of deposits of cholesterol fibers and dead muscle cells.
            • They bulge into the lumen of the artery causing it to narrow so that the blood flow through it is reduced.
        • Atheromas increase the risk of two potentially very dangerous conditions: thrombosis and aneurysm
          • Thrombosis
            • If an atheroma breaks through the endothelium of the blood vessel it forms a rough surface that interrupts the otherwise smooth flow of blood.
              • This may result in the formation of a blood clot, or thrombus, in a condition known as thrombosis.
                • This thrombus may block the blood vessel reducing or preventing the supply of blood to tissues beyond it.
                  • The region of tissue deprived of blood often dies as a result of the lack of oxygen glucose and other nutrients that the blood normally provides.
                    • Sometimes the thrombus is carried from its place of origin and lodges in and blocks another artery.
          • AQA BIOLOGY
          • Aneursym
            • Atheromas the lead to the formation of a thrombus also weaken the artery walls.
              • These weakened points swell to form a balloon like blood filled structure called an anuerysm
                • aneursyms frequently burst, leading to haemorrhage and therefore loss of blood to the region of the body served by that artery
                  • A brain aneurysm is known as a cerebrovascular accident (CVA) or stroke
    • Myocardial infarction (heart attack)
      • This term refers to a reduced supply of oxygen to the muscle of the heart
        • It results from a blockage in the coronary arteries.
          • If this occurs close to the junction of the coronary artery and the aorta, the heart will stop beating because its blood supply will be completely cut off
            • If the blockage is further along the coronary artery the symptoms will be milder because a smaller area of muscle will suffer oxygen deprivation
    • risk factors associated with coronary heart disease
      • Smoking
        • There are two main constituents of tobacco smoke that increase the likelihood of heart disease
          • nicotine
            • it stimulates the production of the hormone adrenaline which increases heart rate and raises blood pressure
              • as a consequence there is a greater risk of suffering coronary heart disease
            • nicotine also makes the red blood cells more sticky this leads to a higher risk of thrombosis and hence of strokes or heart attacks
          • carbon monoxide
            • combines with haemoglobin in the red blood cells to form carboxyhaemoglobin.
              • It thereby reduces the oxygen carrying capacity of the blood.
                • to supply the equivalent quantity of oxygen to the tissues, the heart must work harder
                  • this can lead to raised blood pressure that increases the risk of coronary heart disease and strokes.
                    • the reduction in the oxygen carrying capacity of the blood means that it may be insufficient to supply the heart muscle during exercise
                      • this leads to chest pain or myocardial infarction
      • High blood pressure
        • lifestyle factors e.g. excessive stress, certain diets and lack of exercise increase high blood pressure which increases the risk of heart disease
          • as there is already a higher pressure in the arteries, the heart must work harder to pump blood into them and is therefore more prone to failure
          • higher blood pressure within the arteries means that they are more likely to develop an aneurysm and burst causing haemorrhage
          • to resist the higher pressure within them the walls of the arteries tend to become thickened and may harden restricting the flow of blood
      • Blood cholesterol
        • cholersterol is an essential component of membranes - it is a biochemical which must be transported in the blood. it is carried in the plasma as tiny spheres of lipoproteins. There are two types
          • high density lipoproteins which remove cholesterol from tissues and transport it to the liver for excretion. They help protect arteries against heart disease
          • low density lipoproteins which transport cholesterol from the liver to the tissues including the artery walls which they infiltrate leading to the development of atheroma and hence heart disease
      • Diet
        • there are a number of things that increase the risk of heart disease
          • high levels of salt raise blood pressure
          • high levels of saturated fat increase low density lipoprotein levels and hence blood cholesterol concentration
        • foods that act as antioxidants e.g. vitamin C reduce the risk of heart disease

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