The blood sugar level is in dynamic equilibrium, ever changing because it is dependent upon the varying balance of supply and demand. The supply of glucose comes from three main sources: absorption of digested polysaccharides and monosaccharides from the intestinal tract, liver glycogen and, lastly, other carbon fragments derived from the glucogenic amino acids, body fat and fractions remaining from partially metabolized glucose. The first and last sources probably contribute the greater share.The crucial step in glucose metabolism appears to be the phosphorylation of glucose, a reaction catabolized by the enzyme hexokinase: Glucose + adenosine triphosphate