So there are two important types of hormones that play a role in actually signaling the breakdown of glycogen in liver cells. And these hormones are glucagon and epinephrine. Now, glucagon plays a much greater role in liver cells than epinephrine, but in skeleton muscle cells, it's epinephrine that actually initiates the breakdown of glycogen. So let's imagine that our body is undergoing starvation. And so what that means is in our blood plasma we have a relatively low concentration of glucose. And to basically increase the level of glucose, the liver cells have to begin breaking down the glycogen into glucose and release that glucose into the blood plasma.