 Pancreatic islets are amazing. They have two kinds of endocrine cells. The beta cells produce insulin. The alpha cells produce glucagon. Now glucagon is my hormone that acts in opposition to insulin. So glucagon is stimulated and released from alpha cells in the pancreatic islets and glucose concentrations decrease. So when glucose levels get too low, glucagon is produced and dumped into the blood. Now what kinds of things would you expect glucagon to do? Its goal is to raise glucose levels. Glucagon acts on the liver, you guys. Why? Because it causes the breakdown of glycogen and it's super powerful. Just a little bit of glucagon is going to cause a major dump of glucose from the liver. Now, here's what you have to know. The liver normally has enough glucose stored in it, like in the form of glycogen, for 20 miles of running. So, I mean, I can't even begin to think of how much energy it would take me to run 20 miles. I guarantee my body would break down and rebel before I could run 20 miles. But the amount of energy that it would take, my liver has that in the form of glycogen stored in there. Awesome. If, okay, so you got that, I just got to write that down for you. You have 20 miles of running, worth of glucose stored in your liver right now. So, you don't have to eat anything, you don't have to add any sugar, you can just go running for 20 miles with that energy. Now, if you secrete glucagon for four hours, just dump glucagon chronically into your blood for four hours, you will deplete all of that. All the glycogen stores will be broken apart and dumped into the blood in the form of glucose after just four hours. The point is that it's extremely potent. And you can imagine that, dude, this is a fantastic example of homeostasis because glucagon is going to raise glucose concentrations, insulin is going to decrease glucose concentrations. So, they're constantly being produced in just little dinky amounts based on what's going on in the blood glucose-wise. How fantastic is that? This lecture gives you many different mechanisms, it gives you many different feedback loops, and it gives you a lot of homeostatic, wow, wow. Okay, that's it. I hope you have a lovely day. Bye-bye.