Glycogen

Sometimes called 'animal starch'. It is stored in liver and muscle cells and can be converted to glucose if needed. Liver glycogen is used to put glucose in the blood when needed. Muscle cell glycogen is not. Glycogen is the primary glucose (energy) storage mechanism.

Glycogen is a glucose polymer. It is generated from glucose by the enzyme glycogen synthase. Its breakdown into glucose, called glycogenolysis[?], is mediated by the enzyme glycogen phosphorylase.