The metabolism of glucose is the vital process of a living body. In glucose metabolism, glucose plays the most important role in providing the human body the energy required for various other works and for survival as well. Once consumed, glucose is absorbed by the intestines leading to the flow into the blood. Extra glucose that is stored in the muscles and liver as glycogen is hydrolyzed to glucose and released into the blood when needed. Glycogen is mobilized and converted to glucose by gluconeogenesis when the blood glucose concentration is low. Glucose may also be produced from non-carbohydrate precursors, such as pyruvate, amino acids and glycerol, by gluconeogenesis. It is gluconeogenesis that maintains blood glucose concentrations, for example during starvation and intense exercise.