Insulin

Insulin is a peptide hormone produced by the beta cells of the pancreas’ islets of Langerhans. It consists of 51 amino acids in two chains, A and B, linked by disulfide bonds, and plays a central role in regulating blood glucose and energy metabolism.

In target tissues, insulin binds to the insulin receptor, triggering a tyrosine kinase–mediated signaling cascade that promotes glucose uptake in liver, muscle, and adipose tissue through GLUT4 transporters. It stimulates glycogen synthesis in liver and muscle, enhances lipid and protein synthesis, and suppresses hepatic glucose production, gluconeogenesis, and ketogenesis.

Endogenous insulin is released in response to rising blood glucose, amino acids, and incretin hormones. Therapeutically, insulin is essential for all individuals with type 1 diabetes and is used in many cases of type 2 diabetes or gestational diabetes when glycemic control requires it, as well as in various acute or perioperative settings.

Insulin therapies include human insulin produced by recombinant DNA technology and a range of insulin analogs with altered absorption and action profiles. Classes include rapid-acting analogs (such as lispro, aspart, glulisine), short-acting regular insulin, intermediate-acting NPH, and long-acting analogs (glargine, detemir, degludec). Inhaled insulin products are also available in some regions. Administration is typically subcutaneous, with continuous subcutaneous insulin infusion pumps used for many patients; intravenous insulin is used in hospital settings for specific indications.

Historically, insulin was discovered in 1921 by Frederick Banting and Charles Best, revolutionizing diabetes care and earning the Nobel Prize in 1923. Modern production relies on recombinant DNA in bacteria or yeast, enabling large-scale manufacturing and the development of analogs. Common safety considerations include the risk of hypoglycemia, weight gain, and injection-site reactions, managed by dosing, monitoring, and site rotation.