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- [Voiceover] Metabolism is just the flow of energy throughout the body. Energy enters our body when we eat food, and that food is then absorbed in three different forms. It can be absorbed as amino acids, so, things that make up proteins, so, you'd imagine meat would have a lot of amino acids. Or they can be absorbed as fats, so these are lipids, or fatty acids and so your greasy, fried food is pretty rich in fats. Or they can be absorbed in carbohydrates, or I'll just write "carbs" here, which you have a lot of in ice cream or other sweet things. Each of these things deliver energy into your GI tract. Your stomach, and your intestines, which can then be absorbed and sent elsewhere for use. Now carbohydrates are one of the main currencies for energy, so let's focus on that, and we'll do so by starting with glucose, which is the most basic form of carbohydrates. In fact, it's considered a simple sugar. Now, there are two main hormones that control the availability of glucose throughout the body. And they're at a constant tug of war with each other. One of them, which you've heard of probably is called "insulin." Insulin regulates that storage of glucose, as we'll talk more about in a minute, and the other guy on the end of the rope, is a hormone called "glucagon." Glucagon regulates the release of glucose from storage. And it's pretty important that we have enough glucose available in the blood. Because, for example, the brain uses about 120 grams of glucose per day. And that's a lot, because it comes out to be about 60 to 70% of all the glucose that we eat in a day. But to put it in terms that I think you and I appreciate a little more, 120 grams of glucose comes out to be about 250 M&Ms, in a single day! Now that's a lot of M&Ms. So you can see why it's really important to have enough glucose available for your essential organs to use. And thankfully, we have these two hormones to help regulate the amount of glucose in our blood. So now let's take a look at how these hormones regulate the amount of glucose in our blood. And let's do that on this graph. So let's say this axis represents time, so over time, we'll see some changes, and this axis over here, the Y axis, will represent the concentration of glucose in our blood. So that's the concentration of glucose. And most commonly, that will be represented in milligrams per deciliter. Milligrams per deciliter. Now, the body likes to keep the amount of glucose in the blood to be no lower than about 70 milligrams per deciliter, and no higher than about 120 milligrams per deciliter. This is sort of the range that I would consider to be the, um (clears throat) sweet spot. Because if we go any higher than 120, then we end up having a condition that's called "hyper," hyper meaning "a lot of," "glycemia." "Hyperglycemia," which just means "a lot of glucose "in the blood." If we have hyperglycemia for a long period of time, that can lead to what's referred to as "eye, nerve, and kidney disease." Eye, nerve, and kidney disease. And we can go into a lot more detail about how this happens, but, just understand that having a lot of glucose in your blood can cause changes to these structures to make them not work as well. And unfortunately this is a fairly common problem. Because another term for eye, nerve and kidney disease is "diabetes." And in fact, if you have a person who's been fasting overnight to come in for a blood test, and you notice that they have more than 126 milligrams per deciliter of glucose on two different occasions, that's grounds for diagnosis of diabetes. On the other hand, if we have very little glucose on our blood, or not enough, that condition is referred to as "hypoglycemia." "Hypo" meaning, "less or low," and then "glycemia" of course meaning "glucose." And some of the things that you can start to notice, if you're hypoglycemic, is that you're tired, maybe you're lethargic, but if this persists, you can even go into a type of coma, or even die from having too little glucose in your blood. And in most people, we start to notice that we're feeling hypoglycemic when we get below 40 milligrams per deciliter. Now usually, our body's pretty good about making sure that the level of glucose in our blood stays within the sweet spot, or within this sweet range. And the way we accomplish this, is through the hormones I just mentioned. So let's imagine that you eat at this point of time right here. And naturally, the level of glucose in your blood will rise, because you've introduced more glucose into your system by eating it. Eventually, your body will notice that your glucose levels are rising, and will counter that by releasing insulin to drive the amount of glucose in your blood down. And that's an important point, because insulin decreases the blood-glucose concentration by storing the glucose in another form. And we'll get into more detail about that in a second. The other thing that could happen is that, you may have a decreasing amount of glucose in your blood. Which, as I mentioned here, is not a good thing to have happen either. What your body does to counter that, is release glucagon to increase the amount of glucose in your blood. And so it's important to remember here as well, that glucagon will increase the serum or the blood concentration of glucose by releasing it from storage. So glucagon does the opposite, it releases glucose from storage. So now that we know how the release of glucagon and insulin can affect blood-glucose levels, let's focus in and see how that happens. So let's start with insulin, and that does a number of things to glucose. But remember, that at the end of the day, all we're doing is storing it. Just remember, insulin causes storage. So, the first thing that insulin does to glucose, is cause it to undergo a process known as "glycolysis." Glycolysis, which you may have heard of before. It's an irreversible process. It's irreversible, alright, irreversible down here. Because it converts glucose into ATP, which is the most basic unit of energy that we use in the body. And that's an important distinction. ATP is energy to be used anywhere in the body. Okay, instead of storing the energy of glucose in ATP, insulin can cause glucose to undergo what's called "glycogenesis." Glycogenesis, which just means "the formation of glycogen." So, glycogen. And glycogen is just a heavily-branched polymer, or molecule that has a whole bunch of glucose molecules stacked on top of it. And this is just energy to be stored in the short-term in mainly the liver, or muscle tissue. So mainly, liver or muscle. And this is a reversible process, because once we make glycogen, we can break it down and release glucose as well. Finally, the last thing insulin can cause glucose to do, is undergo "lipogenesis." Lipogenesis, which I think you can use the suffix to infer here that we are producing lipids, or fatty acids, so lipids or fatty acids, and this is an irreversible process. So this is irreversible, where we store glucose as lipid, and the key here is that we are taking the energy of glucose, and we are storing it long term. Long term, in what's called "adipose tissue." Adipose tissue, or just, the fatty layers within our body. So adipose tissue. Now what about glucagon? What are the processes it uses to release energy or glucose into the blood stream? Let's put it this way. If we're releasing glucose into the blood stream, my question is, what are we releasing it from? Well, the first thing we can release it from, is glycogen. And we just talked about this. We can form glycogen using insulin. Or, if there's a lot of glucagon around, we can have what's called "glyco," "glycogenolysis." Which just means "the breaking down "or the cutting down of glycogen." Now, this is a reversible process, 'cause we can always go and take glucose to make glycogen again. The other thing we can release glucose energy from, is, or rather I should say, are, amino acids. Amino acids can undergo a process known as "gluconeogenesis." So "gluco" meaning "glucose", "neo" meaning "a new," and then "genesis," meaning "to create," or "the creation of." This is also a reversible process that will take amino acids, bunch them together with other things to convert them into glucose. Now finally, the last thing glucagon can do, is to take fatty acid, so fatty acid or your lipid, and instead of converting it to glucose, glucagon will take the fatty acid, and turn it into these things that are called "ketone bodies." Ketone bodies. And it does so through a process known as "keto," short for "ketone," "genesis," meaning "to generate ketone bodies." Now this is an irreversible process. And it's kind of a funky thing that happens within the body, because it's what we do when we're in our starvation mode. When we're not getting the right amount of nutrients of some reason or another. And the reason why this is sort of a last resort, is because ketone bodies are very unique, in that they are energy, forms of energy to be used only, only by the heart and brain. Ketone bodies don't really supply energy anywhere else. So that's why it's sort of a last minute starvation mechanism to provide energy where it's most critically needed to help us survive. So you can sort of see here that there's a tug of war game that goes on between insulin and glucagon. In fact, insulin itself, when it's released into the blood, will inhibit the release of glucagon. Which just goes to show you how opposite their end goals really are. And there's a lot more to talk about how insulin is released, or how glucagon is released and where it comes from, this is a great overview of what they end up doing in the body.