Insulin is a hormone produced by the beta cells located in the islets of Langerhans within the pancreas, an organ situated behind the stomach

. These beta cells secrete insulin in response to elevated blood glucose levels to regulate metabolism by promoting glucose uptake into liver, muscle, and fat cells

. Historically, insulin was first isolated from animal pancreases (mainly bovine and porcine) in the early 1920s, enabling the first commercial insulin products

. However, animal-derived insulin differs slightly in amino acid sequence from human insulin, which can cause immune reactions in some patients. Modern insulin used for diabetes treatment is primarily produced through recombinant DNA technology, where the human insulin gene is inserted into bacteria (such as E. coli) that then manufacture insulin identical to natural human insulin

. This biotechnological method provides an unlimited and consistent supply of insulin, overcoming limitations of animal or human pancreas extraction. In summary:

• Naturally, insulin is made by pancreatic beta cells in the islets of Langerhans

• Early insulin for therapy came from animal pancreases

• Today, most insulin is produced by genetically engineered bacteria using recombinant DNA technology

This evolution in insulin production has greatly improved availability, purity, and safety for people with diabetes.