Glycogen is a polysaccharide, also called animal starch. It is storage form of carbohydrate m in animals. It is synthesized and stored mainly in liver and muscle cells. When the body when the body is not getting glucose from food, the stored glycogen is broken down by the enzyme glucagon secreted from the pancreas to glucose into the bloodstream to be used as fuel for the cells. This biochemical breakdown of glycogen to glucose is called glycogenolysis.