Glycogen

The chief storage form of carbohydrate in animals (including humans). Glycogen is stored mainly in the body’s liver and muscle tissue. When blood glucose levels are high, excess glucose normally is stored as glycogen. When blood glucose levels drop, glycogen is converted back into glucose.

Prolonged exercise can deplete a person’s glycogen stores. This means that people with diabetes can develop severe hypoglycemia (low blood sugar) many hours after exercise, as the body replenishes its supply of glycogen in the muscles and tissues by taking glucose from the blood.

Two hormones control the breakdown of glycogen: epinephrine (adrenaline), released by the adrenal glands, and glucagon, secreted by the alpha cells of the pancreas. After many years of diabetes, these hormones may fail to work properly. The timely breakdown of glycogen into glucose may thus not occur, making people more prone to episodes of severe hypoglycemia without warning.

Glucagon in injectable form is commercially available in special kits for treating severe hypoglycemia. Because someone whose blood sugar drops to very low levels may be unable to treat himself, friends and family of people with diabetes should learn how to inject glucagon. Injected glucagon quickly converts glycogen back into glucose to help restore normal blood sugar levels.