The liver in glucose regulation
The liver is a large and important organ, with many functions, which lies across the top and towards the right of the abdomen. As you already know, it is important in helping to control glucose levels, by storing excess glucose and releasing it back into the blood when the level falls too low. Insulin stimulates the liver to take up glucose and change it into glycogen, a substance made of chains of glucose units stuck together. You can think of glycogen as a storage form of glucose.
If there is plenty of glucose in the blood, the body makes glycogen to use later, at times when glucose is scarce. For example, to keep the blood glucose level constant in the body overnight (when one is not eating), the liver slowly releases glucose from its glycogen stores. After a meal when there is plenty of glucose in the blood, the liver stores glucose as glycogen again. Similarly, when you exercise and need additional fuel, the liver can slowly release glucose to provide energy.