Functions of Blood Cholesterol
Membrane structure and fluidity
Synthesising steriod hormones
Synthesising vitamin D
Cholesterol is insoluble in blood plasma so it is transported by lipoproteins, which are made in the liver.
The centre of a liporprotein contains cholesterol and other lipids (triglycerides and steroids). They are coated in a single phospholipid layer, with proteins to make it soluble.
High Density Lipoproteins
More proteins, fewer lipids
Remove cholesterol from tissues and return it to the liver
HDL receptors on liver cells
Decrease blood cholesterol and fat deposists
Decrease rate of formation of atheromas (plaques)
Low Density Lipoproteins
More lipids, fewer proteins
Deliver cholesterol to tissues from the liver
LDL receptors on tissue cells
Raise blood cholesterol and fat deposits
Increase rate of formation of atheromas (plaques)
If the endothelial lining of an artery is damaged, LDLs tend to deposit fat and cholesterol in them.
This accumulates along with fatty acids, calcium salts and fibrous tissues, forming an atheromatous plaque.
Atherosclerosis is the stiffening and hardening of the artery walls caused by a build-up of plaque.
This leads to a bulge in the artery wall which narrows the lumen and restricts blood flow.
If oxygenated blood flow is restricted, the cardiac muscle may become deprived of oxygen and fatigued, causing angina which is severe chest pains.
The plaque deposits also roughen the lining of the artery which increases the risk of blood clots forming.
If the artery is almost completely blocked by atheromatous plaque and blood clots, a heart attack (myocardial infarction) may occur.
Cardiac muscle is starved of oxygen and cells rapidly die. This may be fatal.