Question

Does betta oxidation of fatty acids occur in every cell of the body? More specifically is it confined to the liver (as does fatty acid synthesis), or occurs in other tissues too?

Answer 1

The b-oxidation of long-chain fatty acids is central to the provision of energy for the organism and is of particular importance for cardiac and skeletal muscle. However, a number of other tissues, primarily the liver, but also the kidney, small intestine and white adipose tissue, can utilize the products of b-oxidation for the formation of ketone bodies which can, in turn, be utilized for energy by other tissues.

Under fasting conditions, the insulin : glucagon ratio is low which results in the stimulation of lipolysis. Triacylglycerol stores in fat depot are hydrolysed to free fatty acids that are then released into the circulation and subsequently taken up and oxidized by most tissues apart from the CNS and erythrocytes. In the liver, under these conditions, fatty acids are broken down to acetyl-CoA, most of which is used for the formation of ketone bodies (acetoacetate and 3-hydroxybutyrate). Ketone bodies are, in turn, exported for oxidation by extra-hepatic tissues. Simultaneously, glycogenolysis occurs, and in the liver, and to a lesser extent the kidney, glucose is mobilized for extra-hepatic utilization. Skeletal muscle also has substantial glycogen reserves, but these are utilized endogenously particularly during exercise. Thus the net affect of fasting or indeed any stress leading to counter-regulation of insulin, is a switch from a fuel economy based on carbohydrate to one in which a greater proportion of energy is derived from the oxidation of lipid.