Most of the dietary fat is absorbed into the blood in chylomicrons. Triglyceride is removed from the chylomicrons by lipoprotein lipase in the blood, fatty acids released are taken up by the adipose tissue (Fat storage tissue) and the chylomicron ramnants are removed by the liver.Triglyceride taken up by the liver is broken down to 2-carbon fragments which are used in many metabolic processes. Free fatty acids liberated by the adipose tissue is also taken up by the liver and used in simillar way.
In these processes lipid aggregates are formed containing triglycerides, phospholipids and cholesterol. These are combined with apoproteins to form Lipoproteins which are released into the blood.
These Lipoproteins are:
1. VLDL – Very Low Density Lipoproteins
2. IDL – Intermediate density Lipoproteins
3. LDL – Low Density Lipoproteins
4. HDL – High Density Lipoproteins
The density of the lipoproteins is determined by the relative protein and lipid content with high density lipoproteins containing high protein and less lipids.
The liver synthesises more cholesterol than any other organ. The cholesterol is incorporated into lipoproteins or converted to bile acids or excreted into bile. In biliary obstruction of any kind serum lipid concentration increases mainly due to formation of abnormal lipoprotein known as Lipoprotein X.