Insulin is a hormone produced by the pancreas that regulates the level of glucose, a simple sugar that provides energy, in the blood.

The human body requires a steady amount of glucose throughout the day, and that glucose comes from the foods we eat. Obviously, though, we don't spend our entire day eating a bit of food at a time to maintain a steady stream of glucose. This is where insulin comes into play.

When glucose levels are high, insulin stimulates cells in the liver, muscles and fat. Liver and muscle cells combine glucose into a compound called glycogen, essentially storing the energy for later use. Insulin also removes other by-products of food from the body by stimulating fat cells to form fats from fatty acids and liver and kidney cells to turn amino acids into proteins. Finally, insulin prevents the liver and kidneys from producing glucose from partially-metabolized materials, a process that can damage these organs over time.

Insulin is closely related to glucagon, another hormone secreted by the pancreas. Glucagon is called into action when blood-sugar levels are low. It stimulates the liver and muscles so that they will break down the glycogen that was created through the intervention of insulin. Together, insulin and glucagons represent a complete cycle of blood-glucose control.

Insulin works in the body day after day, without anyone giving it much thought. In fact, most people don't know anything about insulin until they learn that they or someone in their family has diabetes. This illness is caused when the body begins to have problems with insulin. In Type 1 diabetes, the pancreas stops producing insulin; in Type 2 diabetes, the body becomes resistant to the insulin the pancreas produces. Type 2 diabetes can usually be controlled through diet and medication, but Type 1 diabetes requires injections of synthetic insulin so that the body can process glucose. Since insulin is such an integral component to body function, it is vital that diabetes be carefully controlled to prevent organ damage.