The hormone Insulin
It is doubtful that there is another hormone that has so many and wide-ranging actions as Insulin. It is the major actor in control of carbohydrate, lipid and protein metabolism. These aspects are well-discussed in all good medical biochemistry texts, and are summarized in the following figure, modified from Clinical Biochemistry, Gaw et al. Insulin signals a state of energy abundance, and activates glucose uptake, metabolism and storage as glycogen in muscle and fat tissue. These organs make up most of the body's mass. At the same time, insulin restrains processes that release stored energy; lipolysis and ketogenesis,glycogenolysis, proteolysis and gluconeogenesis. Insulin is necessary for uptake ofamino acids to tissues and for protein synthesis. Insulin is the central actor in homeostasis; the stabilization of the internal milieu.