Blood glucose level is controlled by two hormones, insulin and glucagon. These are produced by the pancreas. If the blood glucose (sugar) level is too high, then insulin is released. This causes glucose in the blood to be moved into body cells, and it also causes the liver and muscles cells to convert glucose into glycogen and store it. So the amount of glucose in the blood has decreased.If the blood glucose level is too low, then glucagon is released. This causes the glycogen stored in liver and muscle cells to be converted back to glucose, which gets released back into the blood. So the amount of glucose in the blood has increased. When the blood glucose level returns to normal there is negative feedback (this is a key phrase to remember) to the pancreas. This means that the pancreas will stop releasing hormones once there is a normal glucose level again, because they are not needed.