And so when liver cells actually break down glycogen into glucose, they can release that glucose into the blood and that helps our body maintain the correct level of glucose in our cardiovascular system. Now, what I'd like to discuss in this lecture is what ultimately is the signal that initiates the breakdown of glycogen in our liver cells as well as in our skeletal muscle cells. So let's begin by focusing on liver cells. 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.