The blood glucose level is maintained by the joint but antagonistic action of insulin and glucagon. Insulin is hypoglycemic hormone while glucagon is hyper/glycemic hormone.
When there is excess sugar in the blood, more insulin is secreted by the pancreatic islets. This causes the conversion of blood glucose into glycogen. This process is known as glycogenesis. This causes decline in the level of glucose in the blood.
When there is less blood glucose level then the glucagon is secreted. It causes stored glycogen to be converted into glucose. This process is called glycogenolysis.