Glycogen is often referred to as animal starch. It is the most important carbohydrate used for energy storage in animal cells. It is also found in some fungi, but not in plants.
Glycogen is similar to amylopectin, which is one of the two components of starch. The monomer in amylopectin is $$\alpha$$-glucose monomers which is linked by 1-4 and 1-6 glycosidic bonds.
Glycogen does not contain amylose (the unbranched component of starch). This makes glycogen more branched than starch.
The higher number of branches makes glycogen less stable and easier to break down. This makes glycogen well-suited for the fast-changing energy demands of animals.
Glycogen is the first source of energy that the body will use up. This source is depleted after just a few hours of fasting.
The largest stores of glycogen are found in the liver. The hormone insulin triggers glycogen production and storage. The hormone glucagon triggers the breakdown of glycogen to glucose.