Insulin is a hormone produced by the endocrine pancreas. It lowers the sugar level in the blood, causing most of the body's cells to take up glucose from the blood, including liver, muscle, and fat tissue cells, storing it as glycogen in the liver and muscle. When insulin is absent, or low, glucose level in the blood goes up. As its level is a central metabolic control mechanism, its status is also used as a control signal to other body systems such as amino acid uptake by body cells.Composed of 51 amino acid, insulin is a peptide hormone which is produced in the islets of Langerhans in the pancreas. Insulin's structure varies slightly between species of animal. Pig insulin is especially close to the human version.