ABSTRACT
Four major classes of lipids circulate in the blood: cholesterol and cholesteryl esters, triacylglycerols (colloquially, and more frequently, referred to as ‘triglycerides’), phospholipids and free (i.e. non-esterified) fatty acids. All are essential to the normal function of the body. All are poorly soluble in water and therefore cannot be transported in solution in the plasma. Free fatty acids are transported bound to albumin, but the other lipids circulate in the plasma in lipoproteins, which are complex particles containing lipids and one or more of various apolipoproteins. Some apolipoproteins have a structural role; other functions include receptor recognition and the activation (and possibly inhibition) of enzymes involved in lipid metabolism. The function of the major apolipoproteins, which have an alphabetical classification and are abbreviated apo A, apo B, etc., are indicated in Table 5.1.
