Insulin is a polypeptide hormone with a molecular weight of 6 kDa, composed of two peptides chains, A and B, cross-linked by two disulfide bonds and synthesized by the b cells of the islets of Langherans of the pancreas. Insulin influences many metabolic functions of the body. Its best known action is to lower the blood glucose concentration by increasing the rate at which glucose is converted to glycogen in the liver and muscle, and to fat in adipose tissue, by stimulating the rate of glucose metabolism, and by depressing gluconeogenesis.