As can be deduced from their structure, lipoproteins sequester lipids during their transport through plasma. Triglycerides are transported from sites of synthesis and absorption, to sites of utilisation and storage. Cholesterol is transported to cells of the body where it forms part of critical structural components of cell membranes (all cells), or is used for bile acid synthesis (liver), for steroidogenesis (adrenals, gonads), and as a precursor for vitamin D (skin). These functions are achieved by the exogenous (Fig. 6.4) and endogenous (Fig. 6.5) metabolic pathways of lipoprotein metabolism and by the metabolism of HDL.
