Well, one reason is because cells such as our brain cells depend solely and almost entirely on glucose molecules for energy. And so what that means is the brain cells need to take the glucose from the blood to actually use the glucose as an energy source. And that's why the liver must actually maintain and regulate the proper concentration of glucose inside our blood. So, for instance, if our blood level glucose is very low, then what these liver cells will do is they will break down the glycogen as we'll talk about in a future lecture, into Glucose release the glucose inside the Blood. And that will increase the level of glucose to the correct level. So cells such as liver cells can use glycogen to regulate blood glucose levels of the body.