TRIGLYCERIDES: MOVEMENT OF LIPIDS – LIPOPROTEINS
By: Chris teeor.
TRIGLYCERIDES: (continued):
MOVEMENT OF LIPIDS - LIPOPROTEINS:
Lipids and proteins combine together without the aid of a covalent bond to form what is known as lipoproteins. A cell in the intestinal wall makes it possible for the lipids – phospolipids, free cholesterol, cholesterol ester and triglycerides - to come together as a cluster. Then the cluster is bundled up with a coat of protein in order to form a lipoprotein. Lipoprotein functions in the blood plasma as a vehicle to transport cholesterol as well as triglycerides and is referred to as plasma lipoprotein.
Apolipoproteins mix with lipids to create several varieties of lipoprotein particles. The prefix Apo denotes the protein in its lipid free state. Different blends of lipids and proteins produce particles of different densities, such as chylomicrons, high-density lipoproteins.etc. Every blend of lipoproteins has specific functions to perform. The following table illustrates this: (it is based on weight percentage.)
HUMAN BLOOD PLASMA LIPOPROTEINS - MAJOR CAATEGORIES:
Lipoprotein protein phospolipid free cholesterol cholesterol Triglycerides
Esters.
Chylomicron 2 9 1 3 85
VLDL 10 18 7 12 50
LDL 23 20 8 37 10
HDL 55 24 2 15 4
Chylomicron: They are the least dense and largest of lipoproteins containing a large proportion of triglycerols. Intestinal walls do contain epithelial cells. ( The endoplasmic reticulam of the epithelial cell systhesize chylomicron ) Chylomicrons move through the villi of the intestine and absorbed into the lymphatic system from where it easily enters the blood stream. Chylomicrons makes it possible for the triglycerides to tissues for their immediate consumption or to be stored as fat for future use.
Very Low Density Lipoproteins (VLDL) : Liver assess the availability of fatty acids and if what is availabale is more than the immediate requirement for use as fuel, it converts the excess availability into triglycerols and wrap it up with appropriate apolipoprotein which is known as Very Low Density Lipoprotein. VLDL is transported from liver through blood plasma to muscles for its immediate energy needs and to adipose tissues for storage as fat.
Low Density Lipoprotein (LDL) : When VLDL distributes triglycerols, its contents of other lipids such as phospolipids, cholesterol, cholesteryl esters etc., remain high. The loss of triglycerols necessitates some quantity of VLDL to be converted into what is known as Lowe Density Lipoprotein (LDL). LDL is known as bad cholesterol. When it is carried in the blood plasma it has a tendancy to litter the cholesterol on its way making the blood vessels prone to getting clogged. A clogged blood vessel is the rudimentary cause for many chronic diseases some of which may even turn very dangerous.
High Density Lipoproteins: (HDL) : Another important lipoprotein class is known as High Density Lipoproteins (HDL): The HDL springs from small intestine as well as liver. It mainly contains protein rich particles with very negligible amount of cholesterol and cholesteryl esters. (Refer table given above). It is termed as good cholesterol as it works as a scavenger and collects a majority of cholesterol littered by LDL.