Insulin is a peptide hormone that plays a central role in the regulation of glucose and fat metabolism in the body. It is synthesized by the beta cells in the islets of Langerhans in the pancreas and is released in response to high levels of glucose in the blood. Insulin promotes glucose uptake and utilization in the liver, muscle, and adipose tissue and inhibits glucose production in the liver. It also stimulates the uptake and storage of lipids in adipose tissue and inhibits their release. Dysregulation of insulin secretion or action can lead to metabolic disorders such as diabetes mellitus.