The liver lies towards the right of the abdomen, as you saw in Figure 1. It is a large and important organ in the body, with many functions. It is important in helping control glucose levels, which it does by storing glucose. To do this it changes glucose 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 (fasting), the liver slowly releases glucose from its glycogen stores. After a meal when there is plenty of glucose, the liver stores it again. Similarly when you exercise and need fuel the liver can slowly release glucose to provide energy (see Figure 4).
It is also useful to know that insulin (which we shall discuss later in Section 3.7) tends to stimulate the liver to take up glucose.