Insulin is produced by the pancreas. As a hormone, only insulin can lower the concentration of sugar in the blood. It ensures the absorption of sugar in fat, liver and muscle cells. Glycogen is a storage form of sugar and connects many glucose molecules in the liver and muscle cells. After ingesting food, the body secretes insulin, which is then released from the digestive tract into the blood in large amounts of glucose.
Glucagon causes a rise in blood sugar levels and is the antagonist of insulin. When the blood sugar level is low, it is mainly released between meals. It primarily acts on the liver where the formation of new sugar takes place and promotes the breakdown of glycogen. Glucagon inhibits the breakdown of sugar (glycolysis). As a result, the newly formed glucose is not used up again in the liver cells and is released into the blood. The release of glucagon is inhibited by a high glucose level.
Adrenalin, cortisol, thyroxine (thyroid hormone) and somatotropin (STH), a growth hormone, increase the blood sugar level.