Illustration of an insulin hexamer. This is the inactive storage form of insulin, a hormone produced by the pancreas. Insulin consists of two peptide chains, A and B, which are linked by disulphide bridges. The hexamer form has three of each subunit. Insulin is released from the pancreas when blood sugar levels are high, for example after a meal. It instructs liver, muscle and fat cells to absorb the glucose and store it as glycogen (liver and muscle) or fat. Insufficient production of insulin leads to an accumulation of glucose in the blood causing diabetes.