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Insulin and glucagon

Unpack the body's energy dynamics with a focus on metabolism, insulin, and glucagon. Learn how these hormones manage glucose levels, influencing our health. Get to know the processes of glycolysis, glycogenesis, lipogenesis, glycogenolysis, gluconeogenesis, and ketogenesis.
Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video.

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  • leaf red style avatar for user Rose
    Wouldn't the relationship between insulin and glucagon be a negative feedback loop?
    (16 votes)
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  • leaf green style avatar for user Courtney Smith
    Why does he say that glycolysis is irreversible if gluconeogenesis also exists? ()
    (7 votes)
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    • leaf orange style avatar for user Tony Wang
      Because glycolysis is a procedure which involves specific enzymes which only work in one direction. Meaning they work to only synthesize the products of glycolysis and the enzymes themselves cannot work in reverse. Gluconeogensis is actually a similar process to glycolysis but the "the unidirectional enzymes" used in glycolysis are replaces with enzymes which can go in the other direction. This is why the presenter said that glycolysis is irreversible. By definition, the specific enzymes of glycolysis cannot run the reaction in reverse. So based on semantics, glycolysis is irreversible. Hope this helps.
      (12 votes)
  • blobby green style avatar for user zohaansarii
    How does insulin directly pass into the blood through the digestive system?
    (3 votes)
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    • piceratops sapling style avatar for user toastayy
      Insulin is released from the pancreatic B-cells when there is a high conc of glucose in the blood. The glucose enters the beta-cells from a GLUT 2 transporter in the liver, where a number of process occur, and preformed proinsulin is cleaved to insulin and then released.
      When the preformed insulin is depleted, the pancreas also makes Insulin via gene expression.
      (6 votes)
  • duskpin ultimate style avatar for user Ashlie Bloom
    So when we exercise (specifically on an empty stomach), is it accurate to say we burn through our glycogen stores and resort to ketogenesis? How do we "lose" fat / weight?
    (5 votes)
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  • purple pi teal style avatar for user Jess
    Is ketogenesis the process that is happening during diabetic ketoacidosis?
    (2 votes)
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    • starky ultimate style avatar for user Levi Schiefer
      Correct. The body (specifically, pancreatic B-cells) is unable to produce insulin, which functions to allows cells to uptake glucose from the blood. Since the cells unable to access the glucose (which is eventually excreted in urine), they must turn to alternative energy forms, i.e. ketones, which can accumulate in the blood, lowering its pH, which interferes with oxygen transport.
      (4 votes)
  • female robot grace style avatar for user Anna
    So does that mean that ketone bodies are formed constantly in adipose tissue to supply the heart and brain with a lot of energy no matter the situation and thus the deeper we think and the more we exercise the more likely we are to be in a state of ketosis(which is very common in bodybuilders)?
    (0 votes)
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    • male robot hal style avatar for user Abid Ali
      Ketones are really only used by the body when glycogen stores are depleted. In that case, the liver will convert fatty acids to acetyl-CoA, which will then go on to form ketones that the brain and heart can use. This will normally happen in cases of starvation and does not occur constantly in a person who has a normal diet. In contrast to ketone synthesis, when blood glucose levels are low, the liver can also convert fatty acids to acetyl-CoA. Acetyl-CoA can then be used to form ATP. This newly formed ATP can be used in gluconeogenesis to make new glucose and ensure there is plenty of glucose in the blood. The body has many backups before resorting to ketone synthesis.
      (8 votes)
  • starky sapling style avatar for user Sal Daddario
    How do red blood cells use ketone bodies if they do not have mitochondria?
    (2 votes)
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  • duskpin ultimate style avatar for user oskargonzalez
    Im still not clear about after glycogen storage is depleted, how amino acid catalysis is halted and exchanged for ketone formation. That switch over, how long does that take and why does it take that long?
    (2 votes)
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    • piceratops sapling style avatar for user toastayy
      Well amino acid catalysis shouldn't be halted since in a fasting state, the body needs a steady supply of glucose for the brain and red blood cells. amino acids like Alanine are used to generate pyruvate, and from pyruvate generate glucose for the organs previously mentioned. Ketone bodies are also formed in a low carb state, but these are formed from the break down of Acetyl CoA (Acetyl CoA can be made from lipolysis), which can then be used to fuel other organs such as the brain and muscles.
      (1 vote)
  • blobby green style avatar for user Noluthando Gasa
    What would cause insulin and glucose to simultaneously rise or drop?
    (2 votes)
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  • duskpin sapling style avatar for user Me
    Fatty acids can be broken down for energy. Would it fair to say that adipose tissue is converted into useable energy in the same way (i.e., formation of ketone bodies)? It sounds like the only way we can get rid of the long-term energy storage is to be in "starvation" mode. I am not sure how that works in terms of exercising since ketone bodies only supply energy to the brain and heart.
    (1 vote)
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Video transcript

- [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.