Insulin is a hormone produced and secreted by the pancreas or administered by injection, that is necessary for glucose (in the blood) to be transported into cells where it is converted into energy. The only tissues that do not require insulin to transport glucose into cells are the brain and heart.nsulin is a hormone made by the pancreas that helps the body store and use glucose. Think of insulin as the U.S. Postal Service and glucose as the mail; insulin is responsible for delivering that glucose (sugar) from the bloodstream into muscle, fat, liver, and most other cells so that your body can use it for fuel.