Pancreas and insulin. Light micrograph of a cross section through pancreas tissue with a computer artwork of an insulin molecule superimposed on it. In the background (pale pink and white) are islets of Langerhans that secrete insulin. The insulin molecule consists of two chains of amino acids (blue), an A chain (longer) and a B chain (shorter). The two chains are joined by disulphide bridges (yellow). Insulin is responsible for regulating sugar levels in the blood. Insufficient insulin leads to diabetes mellitus where large amounts of sugar are present in the blood and urine. This condition can be treated by injections of insulin.