Insulin is a hormone produced in the pancreas. Insulin is necessary to move sugar from the blood into other tissues, where it is needed for energy production. Insulin also helps metabolize fats, carbohydrates, and proteins. Insulin is the crucial element in diabetes (the pancreas does not produce enough insulin). Persons with insulin dependent diabetes must be injected with insulin. Insulin shots can help control diabetes, if taken regularly. People with diabetes may gradually develop blood vessel, kidney or eye problems, particularly if diabetes is not treated.
Insulin is a protein, like most hormones. Insulin is secreted by the pancreas with the assistance of islet cells. The pancreas, located behind the stomach, also produces digestive enzymes and other hormones. Carbohydrates are absorbed from the intestines into the bloodstream after each meal. Insuin is secreted by the pancreas in response to this increase in blood sugar. Most cells of the body have insulin receptors which bind the insulin already in circulation. When a cell has insulin attached to its surface, the cell activates other receptors designed to absorb glucose from the blood into the cell.
Without insulin, one could eat full meals and actually be in a state of starvation, since many cells cannot access the calories contained in the glucose very well without sufficient insulin.