Insulin is a hormone produced by beta cells in the pancreas that regulates glucose levels. It is composed of two chains of amino acids that are linked together. Glucose triggers the release of insulin which binds to receptors on cells to stimulate glucose and amino acid uptake and inhibit gluconeogenesis. Diabetes occurs when there is insufficient insulin production or the body does not respond properly to insulin, leading to high blood glucose levels and damage to organs over time. The two main types are type 1 diabetes caused by autoimmune destruction of beta cells, and type 2 diabetes related to insulin resistance.