<P> Due to the way glycogen is synthesised, every glycogen granule has at its core a glycogenin protein . </P> <P> Glycogen in muscle, liver, and fat cells is stored in a hydrated form, composed of three or four parts of water per part of glycogen associated with 0.45 millimoles of potassium per gram of glycogen . </P> <P> As a meal containing carbohydrates or protein is eaten and digested, blood glucose levels rise, and the pancreas secretes insulin . Blood glucose from the portal vein enters liver cells (hepatocytes). Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase . Glucose molecules are added to the chains of glycogen as long as both insulin and glucose remain plentiful . In this postprandial or "fed" state, the liver takes in more glucose from the blood than it releases . </P> <P> After a meal has been digested and glucose levels begin to fall, insulin secretion is reduced, and glycogen synthesis stops . When it is needed for energy, glycogen is broken down and converted again to glucose . Glycogen phosphorylase is the primary enzyme of glycogen breakdown . For the next 8--12 hours, glucose derived from liver glycogen is the primary source of blood glucose used by the rest of the body for fuel . </P>

Where does glucose released into the blood end up