thumb|300px|2-D cross-sectional view of glycogen. A core protein of glucose units. The entire globular granule may contain approximately 30,000 glucose units.">is surrounded by branches of glucose units. The entire globular granule may contain approximately 30,000 glucose units.]thumb|300px|A view of the glucose units in a glycogen molecule.">structure of a single branched strand of glucose units in a glycogen molecule.] Glycogen is the molecule that functions as the secondary long-term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach. Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal starch, having a similar structure to amylopectin. Glycogen is found in the form of granules in the cytosol in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the energy reserves of triglycerides (lipids). In the liver hepatocytes, glycogen can compose up to 8% of the fresh weight (100–120 g in an adult) soon after a meal. Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a much lower concentration (1% to 2% of the muscle mass), but the total amount exceeds that in the liver. However the amount of glycogen stored in the body, especially within the red blood cells liver & muscles, mostly depends on physical training, basal metabolic rate and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo. Read more... or Edit at Wikipedia...