Insulin is a peptide hormone produced by secretion from pancreatic beta-cells and some sclerotinian bruit bodies. It plays an important role in sugar, fat and protein metabolism by facilitating the uptake of glucose from the blood by fat, liver and skeletal muscle cells. Glucose absorbed by these tissues is converted to glycogen or fat (triglycerides), with the exception of the liver, where absorbed glucose can be converted to glycogen and fat. Glucose production in the liver is strongly inhibited by high blood insulin concentrations. When blood insulin is high, it is an anabolic hormone that facilitates the conversion of small molecules in the blood into large molecules in the cells. At low concentrations of insulin in the blood, it has the opposite effect by promoting extensive catabolism. When pancreatic beta cells are destroyed by autoimmune processes, insulin is no longer synthesized or secreted into the bloodstream, which in turn leads to type 1 diabetes. A combination of genetic susceptibility and environmental factors leads to insulin resistance, which is type 2 diabetes. In addition, excess insulin production by pancreatic beta cells or reactive hypoglycemia have been associated with insulinomas.