Heart Disease
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
Nicotine constricts arteries causing platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases BP
↑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
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