Glycogenolysis: It is breakdown of glycogen to glucose by means of the reaction series shown in figure 6.11 Like glycogenesis it also occurs in all body cells , But mainly in liver and muscle cells ,to yield glucose required for energy production , Muscle cells use this glucose themselves, but liver cells release it into the blood to replenish the amount of glucose that is being constantly taken up by body cells from the blood .Thus glycogen storage of liver serves to maintain normal blood sugar level in between meals. It is thus a reserve fuel, A fasting or starving person first consumes this liver glycogen. All of it is consumed in 12to 24 hours if not replenished by another meal.
Glycogensis and glycogenolysis are regulated by double control nervous as well as hormonal. Hormonal control involves five main hormones insulin hormone of pancreas, growth hormone of pituitary and cortisol of adrenal cortex stimulate glycogenesis whereas glucagon of pancreas and adrenaline of adrenal medulla stimulate glycogenolysis.