Biological basis of Heart Disease

CHD affects the coronary arteries that supply the heart muscle with the glucose and oxygen it needs for respiration.

Atheroma

Fatty deposit that forms in the wall of an artery. Begins as fatty streaks that are accumulations of white blood cells that have taken up LDLs > enlarge into an irregular patch (atheromatous plaque) - made up of cholesterol, fibres and dead muscle cells > bulge into lumen > blood flow restricted > increased risk of thrombosis & aneurysm

Thrombosis

Atheroma that breaks through the endothelium of blood vessel > rough surface > disrupts blood flow > result in blood clot or thrombus. Thrombus may block blood vessel > reduces/prevents blood flow to tissues beyond it > Region of deprived tissue dies due to lack of oxygen, glucose other nutrients. Thrombus may be carried to and block another artery.

Aneurysm

Atheroma and thrombus weakens artery walls > weak points form balloon-like blood-filled structure (aneurysm) > can burst > haemorrhage > CVA (stroke)

Myocardial Infarction

Reduced supply of oxygen to the myocardium muscle.

Results from blockage in coronary arteries > if occurs close to junction of coronary artery and aorta > heart stops = no blood supply. If blockage further along > More mild symptoms > small oxygen deprived region

Smoking

Carbon monoxide - combines easily and irreversibly with haemoglobin in red blood cells > reduces oxygen-carrying capacity. To supply efficient oxygen, heart has to work harder > raised BP > increased risk of CHD and stroke. Oxygen-carrying capacity may be insufficient to supply heart during exercise > Chest pain (angina) > MI

Nicotine - stimulates production of Adrenaline > increases HR and BP > Higher risk of CHD / stroke. Also makes red blood cells more 'sticky' > increased risk of thrombosis, strokes, MI.

High blood pressure

Higher pressure in arteries > heart works harder to pump blood into them > prone to failure. Higher pressure within arteries > more likely to develop aneurysm and burst > haemorrhage

To resist high pressure within them > walls of artery thicken and harden > restricted blood flow

Blood Cholesterol

HDLs - remove cholesterol from tissues and transport it to liver for excretion - help protect arteries against heart disease.

LDLs - transport cholesterol from liver to tissues, including artery walls > lead to development of atheroma / heart disease.

Diet

High levels of salt - raise BP.

High levels of saturated fat - increase LDL levels and hence blood cholesterol concentration

However antioxidants (Vit C) and non-starch polysaccharides (dietry fibre) reduce risk.