Explanation:
Lipoproteins are basically lipids with a coating of proteins and transport lipids into the bloodstream. The important lipids include Cholesterol and Triglycerides. They are coated with proteins in order to dissolve them in plasma and transport through peripherial tissues.
There are five classes of lipoproteins and they are:
(a) Chylomicrons - Chylomicrons are a type of lipoprotein which transports lipids from mucosal cells of small intestine to the body cells . They are produced in intestinal epithelial cells. They are the biggest lipoproteins.
(b) Very Low Density Lipoprotein - Produced in the liver and function is to carry triacylglycerol in blood. VLDL is also converted into Low Density Lipoprotein. They are the second biggest lipoprotein in terms of size.
(c) Intermediate Density Lipoprotein(IDL) - IDL is produced in the blood and are the remnants after the digestion of triacylglycerol. It is converted into Low Density Lipoprotein. Shorter than Chylomicrons and VLDL but bigger than the other two.
(d) Low Density Lipoprotein(LDL) - LDL is the end product of the digestion of triacylglycerol. They have a high concentration of cholesterol. The function is to carry cholesterol from the liver to the body tissues and cells. They are smaller in size than the above three lipoproteins but bigger than High Density Lipoproteins.
(e) High Density Lipoproteins(HDL) - contains the highest density of protein to lipid ratio and is the most abundant of apolipoproteins. Their main function is the return of cholesterol from peripheral tissues to the liver.
VLDL, IDL, LDL and Chylomicrons all of them are pro-atherogenic because they support atherosclerosis and are involved in direct cholesterol transport.
HDL is anti atherogenic or atheroprotective because of the protective activities against atherosclerosis and it also helps in reverse transport of cholesterol.
