True about insulin is

Insulin is a polypeptide hormone, secreted by b cells in the islets of Langerhans, which promotes glucose use, protein synthesis, and the formation and storage of neutral lipids; available in various preparations including genetically engineered human insulin, which is currently ored. Insulin is used parenterally in the treatment of diabetes mellitus.Ref: Ganong&;s review of medical physiology;24th edition; page no-432