These are the cells that produce insulin, the hormone 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. We wish insulin had a similar mantra as the USPS—neither blood, nor fat, nor DNA will keep insulin from delivering glucose throughout the body—but it doesn't quite work that way. Problems happen when either the pancreas doesn't make enough insulin or various parts of the body block insulin and prevent it from delivering glucose to those cells.