Diabetes (lat. diabetes mellitus) is a disorder in which the level of sugar in the pancreas is elevated, and which occurs when the pancreas stops fully or partially producing the hormone insulin, or the produced insulin is not effective within the organism. The concentration of glucose in the blood controls insulin, a hormone which is secreted by β-cells of the endocrine part of the pancreas. Insulin transports glucose which enters the blood through the gastrointestinal tract, after absorption from food or from the liver, and into the cells of various tissues through the activation of insulin receptors. Elevated concentrations of glucose in the blood occurs when β-cells of the pancreas do not secrete insulin or they do not secrete enough of it, when the cell receptors are resistant to insulin and when the flow of glucose to the blood is unproportionally large. It follows that diabetes is not characterized exclusively by elevated glucose levels in the blood, but also by a total or partial deficiency of insulin. This metabolic disorder refers not only to a disorder of the metabolism and the level of sugar in the blood, but also to a disorder in metabolizing fat and protein. With time, this metabolic disorder causes changes in blood vessels which leads to damage in the cardiovascular system of the kidneys and eyes. Patients with diabetes with a complete lack of insuline have diabetes dependent on insuline, and patients with a partial lack of insuline or with insulin receptor resistance, have diabetes independent of insulin.