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Diseases > Heart Disease
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Coronary Heart Disease

  • Arteries supplying the heart become narrowed and the blood supply to cardiac tissues is reduced
  • Heart has to work harder to force blood through narrowed vessels / blood pressure increases
  • Angina
    • Chest pain due to severe shortage of blood to the heart muscle - cells do not die
    • Pain only occurs during activity but not at rest
    • Caused by narrowing of coronary arteries (atherosclerosis)
  • Heart attack (myocardial infarction)
    • When a coronary artery is totally blocked by a thrombus/embolus
    • No blood supply to heart muscle and cells die - often fatal
  • Heart failure
    • Blockage leads to damage of heart muscle and to gradual weakening of muscle
    • Less efficient pumping
    • Often accumulation of blood on right side → enlargement of heart

Causes of Coronary Heart Disease

  • The main cause is atherosclerosis
  • Often called hardening of the arteries
  • Inner layer of artery wall thickens with deposits of
    • Cholesterol
    • Fibrous (scar) tissue
    • Dead muscle cells
    • Blood platelets
  • Fats, in the form of lipoproteins, accumulate beneath the endothelium
    • Form plaque on the wall of arteries, also called atheroma
    • Arteries become less elastic and partially narrowed
    • Accelerated by high blood pressure
    • Arterial endothelium damage is more likely but also leads to further weakening
  • Aneurysm: weak walls may burst leading to severe loss of blood (haemorrhaging)
    • Brain aneurysm is called a stroke
  • Atheroma increases the risk of blood clotting
    • Thrombus (blood clot) may break away and lodge elsewhere in the circulation (e.g. brain, heart)
    • Circulating thrombus is called an embolus

Cholesterol and Atherosclerosis

  • Cholesterol has important functions and is needed for
    • Vitamin D production in skin
    • Sex hormone production in gonads and adrenal glands
    • Making cell membranes
    • Make bile acid (salts)
  • Cholesterol is an alcohol, not a fat but has properties similar to fats - soft, waxy, and insoluble (difficult to remove if deposits form)
  • Cholesterol is transported in the blood stream from the liver to tissues
    • Safe transport is needed due to its insolubility
    • This is achieved by lipoproteins, which are soluble fatty proteins
    • These are wrapped around the cholesterol
    • Usually, only small amounts of free cholesterol escape
  • Fatty streaks adhere to wall of arteries - Atheroma/atherosclerosis/plaque forms
    • Narrows lumen of artery
    • Damages endothelium
    • Can lead to formation of thrombus/blood clot

Lipo-Proteins

Low density lipo-proteins LDL's

  • Carry cholesterol from the liver to the tissues
  • Normal levels: some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes
  • High levels: too much cholesterol leaks out
    • Cholesterol is deposited on the arterial walls
    • White blood cells are trapped within the cholesterol
    • Free radicals are released by white blood cells and react with cholesterol
    • This damages artery wall which allows further cholesterol deposits (i.e. Atherosclerosis)
    • Blood platelets are activated and stick to damaged areas releasing clotting factors (thromboxanes)
    • Healthy arteries produce anti-clotting factors (prostaglandins)
    • Normally a balance between these two. Healthy vessels do not form clots

High density lipo-protein HDL's

  • Carry cholesterol away from tissues, including artery walls
  • Travels to liver, is broken down and removed with bile

Smoking

  • Reduces levels of antitoxidants (vitamins), more damage due to release of free radials by phagocytes
  • Nicotine constricts arteries causes platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases blood pressure [EXAM]
  • Raises conc. of fibrinogen (in blood) → increased risk of clotting
  • Higher blood pressure causes damage to blood vessel lining/endothelium/collagen [EXAM]
    • Leads to rise on blood platelets and makes them more sticky/form a plug/adhere to collagen fibres
    • Release of thromboplastin/thrombokinase
    • Fibrinogen converted to insoluble fibrin
    • Platelet plug trapped by fibrin mesh
  • Raises blood cholesterol by causing a rise in LDLs in blood
  • Carbon monoxide reduces the efficiency of the blood in terms of carrying oxygen
    • Haemoglobin combines with CO more readily than with oxygen → forms carboxyheamoglobin
    • Associated with plaque formation
  • Principle CHD = heart muscle receives inadequate amount of blood or oxygen/(coronary) blood supply reduced

Treatment

  • Lower blood pressure
    • Drugs which regulate heart rate/beat - prevent abnormal rhythms (beta blockers)
    • Drugs which prevent blood clotting making thrombosis less likely (warfarin)
  • Heart by-pass
    • Vein from the leg is used to by-pass the blocked region of the coronary artery
    • Involves open heart surgery
  • Angioplasty
    • Deflated balloon-like device is passed up to the heart via the aorta
    • Guided into damaged coronary artery and inflated to stretch the artery
  • Transplant
    • Need to find a suitable donor
    • Need to prevent rejection → drugs that suppress immune system needed for rest of life

Prevention is more cost effective then treatment

  • 1. Screen the population for
    • High blood pressure
    • High cholesterol
    • Stop smoking, healthier diet, more exercises
    • Men over 35 are at highest risk
  • 2. Monitor the behaviour of the heart during exercise
    • Difficult but encouraging the population to adopt a more healthy lifestyle from an early age is important
    • Often leads to changes in diet and weight management
  • 3. Giving up smoking and reducing alcohol intake
    • Reduces blood pressure
    • Many people do not heed the advice until it is too late
    • Coronary heart disease is a long-term degenerative disease, starts at birth