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HBIO1 > Heart Disease
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Atherosclerosis

  • Hardening of arteries
    • Tunica intima thickens with deposits of
      • Cholesterol
      • Fibrous (scar) tissue
      • Dead muscle cells
      • Blood platelets
    • Arteries become less elastic and partially narrowed
      • ↑BP which in turn accelerates atherosclerosis
      • Leads to endothelium damage and weak walls
  • Mechanism
    • Excess cholesterol leaks from lipoproteins (LDLs)
    • Deposited on arterial walls
    • Macrophages (white blood cells) are trapped within cholesterol
    • Release free radicals which damage the arterial wall
    • Activates blood platelets which stick to damaged areas releasing clotting factors (thromboxanes)
    • Forms a plaque which may rupture to produce a thrombus
    • Circulating thrombus is called an embolus
    • Embolus may lodge elsewhere in the circulation (brain, heart arteries)
    • NB: healthy arteries produce anti-clotting factors (prostaglandins) → don't form clots
  • Factors that aggravate atheroma formation / atherosclerosis:
    • Hypertension (↑BP)
    • Smoking (release of free radicals)
    • High LDL and low HDL
    • NB: they all cause endothelial damage

Aneurysm

  • Weak arterial walls may burst leading to severe loss of blood (haemorrhaging)
  • Brain aneurysm is called a stroke

Deep Vein Thrombosis

  • Clots are formed by
    • Endothelial damage (see atherosclerosis)
    • Altered blood components (dehydration, too many platelets)
    • Altered blood flow (stasis of veins) → this is what causes DVT
      • Prolonged immobility
      • Such as paralysis, long-distance flights, lying down for weeks after surgery
  • Thrombus often originates in calf veins
  • Inflammation of vein walls → destroys vein valves
  • Causes leg pain, swelling, and redness
  • Elastic support stockings required for life
  • Prevented by taking aspirin or warfarin which inhibit blood clotting

Coronary Heart Disease

  • Atherosclerosis causes arteries to become narrowed
    • More force required to move blood through narrowed vessels
    • Blood pressure increases
  • Stable angina
    • ↑exercise leads to ↑oxygen requirements by heart
    • Narrowed arteries prevent more blood to pass through
    • Shortage of blood to heart muscle causes chest pain
    • Cells do not die as some blood can still pass through
    • Pain only occurs during activity but not at rest
  • Myocardial infarction (MI)
    • Coronary artery is totally blocked by a thrombus/embolus
    • No blood supply to heart muscle and cells die
    • Irreversible if not treated within 90min
  • Heart failure
    • Prolonged blockage of artery causes damage to heart muscle
    • ↓contractions / ↓cardiac output / ↓pressure generated / less blood leaves heart
    • More blood is stored:
      • on the right side of the heart → enlarged heart
      • in veins → swollen legs and enlarged liver

Lifestyle

Cholesterol

  • Needed for
    • Vitamin D production in skin
    • Sex hormone production in gonads and adrenal glands
    • Making cell membranes
    • Produce bile acid (salts)
  • Has properties similar to fats → soft, waxy, and insoluble (difficult to remove if deposits form)
  • Transported in blood from liver to tissues
    • Safe transport is needed due to its insolubility
    • Achieved by lipoproteins, which are soluble fatty proteins
    • These are wrapped around cholesterol
    • Normally, only small amounts of free cholesterol escape

LDL

  • Low density lipoproteins
  • Carries cholesterol from liver to tissues
  • Normally, some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes
  • Excess LDL/cholesterol → too much cholesterol leaks out and causes atherosclerosis

HDL

  • High density lipoprotein
  • Picks up cholesterol from arterial walls and carries it away from tissues
  • Travels to liver where cholesterol is removed with bile

Smoking

  • antitoxidants (vitamins), more damage due to release of free radicals by phagocytes
  • [exam] Nicotine constricts arteries causing platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases BP
  • [exam] ↑BP causes damage to blood vessel lining / endothelium / collagen
    • 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 conc. of fibrinogen (in blood) → increased risk of clotting
  • ↑LDL causes more cholesterol to leak out 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

  • Medication
    • Beta blockers reduce heart rate and reduce oxygen required by heart
    • Aspirin prevents blood clotting and thrombosis formation
    • ACE inhibitors stabilize plaques → prevent thrombus to break off
    • Statins reduce LDL and increase HDL
  • 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
  • Heart by-pass graft
    • Leg veins and arteries from chest are used to by-pass the blocked region of the coronary artery
    • Involves open heart surgery
  • Reperfusion therapy after a myocardial infarction
    • Angioplasty done within 90 minutes of onset of chest pain
    • May prevent irreversible damage to the heart muscle

Prevention

  • 1. Screen population for
    • High BP
    • High cholesterol
    • Uncontrolled diabetes
    • Smoking? Unhealthy diet? No exercises?
    • Men over 55 and women over 65 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
    • Coronary heart disease is a long-term degenerative disease, starts at birth