Insulin (from the Latin, insula meaning island) is a peptide hormone produced by beta cells of the pancreatic islets, and by the Brockmann body in some teleost fish. It has important effects on the metabolism of carbohydrates, fats and protein by promoting the absorption of, especially, glucose from the blood into fat, liver and skeletal muscle cells. In these tissues the absorbed glucose is converted into either glycogen via glycogenesis or fats (triglycerides) via lipogenesis, or, in the case of the liver, into both. Glucose production (and excretion into the blood) by the liver is strongly inhibited by high concentrations of insulin in the blood. Circulating insulin also affects the synthesis of proteins in a wide variety of tissues. In high concentrations in the blood it is therefore a