The liver plays a central role in glucose homeostasis. After having taken food, and glucose concentration increase followed by insulin secretion, about two thirds of apsorbed glucose is almost immediately stored inside hapatocytes as glycogen. In the next few hours, when the glucose concentration in blood and insulin secretion are decreased, glucose is released back to the bloodstream. Insulin and glucagon are important, but also independent regulatory mechanisams of glucose homeostasis. When the glucose concentration increases significantly, insulin secretion is imminent and the values are retreating to normal levels. On the other way around, decreased values induce glucagon secretion which increases the values to a normal degree. In hypoglycemic state, reduced ammount of glucose in blood has a direct effect on hypothalamus and increases symphatic nerve system activity. Epynephrine released by suprarenal glands cortex causes glucose release from hepatocytes and annuls hypoglicemic condition. As a result of long terms starvation cortisol and growth hormone are released and that decreases the degree of glucose consumption in the majority of the cells in organism that has a positive effect on capability of returning to a normal glucose concentration in blood. This is the point when we have to ask ourselves what the purpos of such precise glucose level regulation is. The answer is that the glucose is the only supstrate which the brain, retinal and stem epithelial cells are able to use in unrestricted ammounts to satisfy their methabolic and energy needs. That is why the concentration of glucose must be held to the certain extention due to the proper nutrition of those tissues.