Glycogen is a polysaccharide that is the principal storage form of glucose (Glc) in animal and human cells.
Glycogen is found in the form of granules in the cytosol in many cell types.
Hepatocytes (liver cells) have the highest concentration of it - up to 8% of the fresh weight in well fed state, or 100-120 g in an adult.
In the muscles, glycogen is found in a much lower concentration (1% of the muscle mass), but the total amount exceeds that in liver.
Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells.
Glycogen plays an important role in the glucose cycle.
The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted.