Glucose cycle The glucose cycle can occur in liver cells due to a liver specific enzyme glucose-6-phosphatase, which catalyse the dephosphorylation of glucose 6-phosphate back to glucose. Glucose-6-phosphate is the product of glycogenolysis or gluconeogenesis, where the goal is to increase free glucose in the blood due body being in catabolic state. Other cells such as muscle and brain cells do not contain glucose 6-phosphatase. As a result, any glucose 6-phosphate produced in those cells is committed to cellular metabolic pathways, primarily pentose phosphate pathway or glycolysis. Flux through the glucose cycle is regulated by several hormones including insulin and glucagon as
Glycogen for internal use and is not shared with other cells. This is in contrast to liver cells, which, on demand, readily do break down their stored glycogen into glucose and send it through the blood stream as fuel for other organs. Glycogen was discovered by Claude Bernard. His experiments showed that the liver contained a substance that could give rise to reducing sugar by the action of a "ferment" in the liver. By 1857, he described the isolation of a substance he called ""la matière glycogène"", or "sugar-forming substance". Soon after the discovery of glycogen in the liver, A. Sanson