what is the significance of glycogen storage in the liver and in the muscle?
By storing glucose as a high molecular weight polymer such as starch or glycogen, a cell can stockpile large quantities of hexose units while maintaining a relatively low cytosolic osmolarity. When energy demands increase, glucose can be released from these intracellular storage polymers and used to produce ATP either aerobically or anaerobically. The human organism can store up to 450 g of glycogen—one-third in the liver and almost all of the remainder in muscle. The glycogen content of the other organs is low. Hepatic glycogen is mainly used to maintain the blood glucose level in the postabsorptive (three to five hours after a meal) phase. The glycogen content of the liver therefore varies widely, and can decline to almost zero in periods of extended hunger. After this, gluconeogenesis takes over the glucose supply for the organism. The glucose, released from glycogen cleavage, passes into the blood to supply other tissues. Muscle glycogen serves as an energy reserve for muscle contraction and is not involved in blood glucose regulation. Muscle does not contain any glucose 6-phosphatase and is therefore unable to release glucose into the blood.