Lipid transport occurs in the plasma as lipoproteins after getting associated with several apoproteins; plasma lipid concentrations are dependent on the concentration of lipoproteins. The core of lipoprotein globules consists of triglycerides (TGs) or cholesteryl esters (CHE) while the outer polar layer has phospholipids, free cholesterol (CH) and apoproteins. The lipoproteins have been divided into 6 classes on the basis of their particle size and density. They also differ in the nature of apoproteins, the ratio of TG and CHE, tissue of origin and fate.
The Lipid transport starts from the intestines. Dietary lipids are absorbed in the intestine with the help of bile acids. Chylomicrons (Chy) are formed and passed into lacteals—reach blood stream via thoracic duct. During the Lipid transport through capillaries, the endothelium bound lipoprotein lipase hydrolyses the TGs into fatty acids which pass into muscle cells to be utilized as energy source and in fat cells to be reconverted into TGs and stored. The remaining part—chylomicron remnant (Chy. rem.) containing mainly CHE and little TG is engulfed by liver cells, which have receptors for the surface apoproteins of chylomicron remnant (Chy. rem.), and digested. Free CH that is liberated is either stored in liver cells after reesterification or incorporated into a different lipoprotein and released in blood or excreted in bile as CH/bile acids, which is the final part of Lipid transport.