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
