The biological benefits of lipids as sources of energy and precursors of cell components have led to the evolution of a complex plasma lipoprotein transport system, through which gram quantities of cholesterol, triglyceride, and phospholipid pass each day. A wide variety of tissues make demands on this pool. The adrenal glands and gonads avidly assimilate lipoprotein cholesterol for the production of steroid hormones, and rapidly dividing intestinal villus cells take up the sterol for membrane synthesis. Metabolically active tissues such as skeletal muscle use plasma triglyceride for energy production, while in times of surfeit this lipid is directed into adipocytes for storage.
Two organs, the liver and intestine, play a particularly important role in corporeal lipid metabolism, and together are responsible for the majority of lipoprotein synthesis and catabolism. In the plasma, lipid transport is regulated by specific apolipoproteins (apo), lipoprotein receptors, lipolytic enzymes and transfer proteins, which act in concert to maintain the balance of cholesterol and triglyceride homeostasis in tissues and plasma; their malfunction may cause or contribute to the development of dyslipidaemia.