Function Of HGH And It’s Biological Impact

We highlight the functions of human growth hormone and how it is released in the body.

Transcript

Speaker 1

Welcome back to the Endocrine system on Catalyst University. My name is Kevin Tolkoff. Please make sure to like this video and subscribe to my channel for future videos and notifications. In this video, we're going to be discussing the functions of growth hormone or as it's called, in humans, human growth hormone or HGH. Now, before we get into the. Specific functions of HDH. Let's review a little bit about how. Growth hormone is released. So up here at the very top of this image we have the hypothalamus and then this thing hanging down is the pituitary gland and on the left side of it, this is actually the anterior pituitary gland. So recall that the hypothalamus generates growth hormone, releasing hormone or GHRH. GHRH enters the. Hypothalamic hypotheses portal system. This network of blood. Vessels that carries GHRH down to the anterior pituitary gland and GHRH there stimulates the anterior pituitary gland to generate HGH or human growth hormone, and another name for this that you'll often see is somatotropin. So if you see this, this is referring to. Normal and from the anterior pituitary gland, growth hormone is released into the blood into the general circulation, where it travels to target tissues. Now we're going to see that it's going to have effects on tissues like adipose tissue, skeletal muscle, bone and the liver. But before we get into all these specific functions. I want to go over the major goal of growth hormone because this major goal is really going to dictate all the specific functions. They all sort of come back to. So the major goal of growth hormone is to provide adequate nutrients for ATP synthesis and protein synthesis. So if we think about all sorts of peripheral cells like let's say skeletal muscles, skeletal muscles are composed of cells that are going to be metabolically active, and in order to. Conduct metabolism. You have to have nutrients like glucose, fatty acids, right, and why do you have to have those nutrients to make ATP? Because ATP is what's going to allow that cell to do work. So in order to have ATP, you have to have nutrients and in order to get that. Nutrients you need something that's going to stimulate the body to allow for the availability of those new. So if you want to do work, you have to have ATP, and if you want ATP, you have to have nutrients and so growth hormone is going to make some changes around the body to increase the availability of those nutrients. And the first two tissues we're going to look at are the liver and adipose tissue now. Adipose tissue is just your body fat and the body fat, of course, is going to contain lipids in. The form of triglycerides. So the first effect that growth hormone is going to have is on adipose tissue where it stimulates lipolysis. Now in general, Lipolysis is a process that breaks down those triglycerides into individual fatty acids, and then those fatty acids are released into the blood well. That makes sense given this goal, because those fatty acids could be taken up by skeletal muscle or other cells that are metabolically active and used to make. ATP so lipolysis and adipose tissues, the. First function. Next, we're going to stop at the liver and see several functions here. OK, now the liver is going to play a major role in increasing blood glucose because the glucose can also go to cells that are metabolically active for ATP synthesis. And the way the liver is going to do that, number one is by activating gluconeogenesis. The liver is the major organ that performs gluconeogenesis, which is the synthesis of. Glucose from non carbohydrate precursors and so if the liver is making glucose by this method, it's going to take that glucose and dump it into the blood and therefore that glucose is going to be available to all sorts of peripheral tissues. The second thing the liver is going to do is glycogenolysis recall that. The liver is one of the two major organs that's going to store glycogen. Remember, glycogen is a polymer of glucose. And so glycogenolysis is breaking that glycogen down into glucose. And of course, just like in the case of gluconeogenesis, the glucose that's created through glycogenolysis is going to be released into. The blood where? It can then go and travel to peripheral tissues, and those tissues can take it up. And make. ATP, OK. So the liver is increasing blood glucose through two major mechanisms. One is through gluconeogenesis and the 2nd is glycogenolysis. Now growth hormone is going to stimulate the liver to do one more thing and that's going to be to release another type of hormone called igfs or insulin like growth factors. We're going to come back to that at the end of this video, so really the effects that growth hormone has on adipose tissue and the liver is to increase the availability. Of nutrients in the blood, specifically glucose, from the liver and mainly fatty acids from adipose tissue and all those nutrients are going to travel in the blood to tissues like skeletal muscle and bone. Where they're going to be taken up, utilized in metabolic pathways to make ATP and that. Allows the cells. To do work and one example of a process that's going to take a lot of ATP is protein synthesis. It's going to take a lot of molecules of ATP just to make one protein and obviously skeletal muscles. As we learned in and. P1 are composed of lots and lots of proteins, OK, but it turns out that growth hormones also going to have some other specific effects on cells of skeletal muscle and bone. Let's explore those. So in skeletal muscle, growth hormone is going to stimulate glucose uptake the way it's going to do that is by increasing the number of transporters in the membrane of the skeletal muscle cells. These are called glucose transporters and if if the muscle cells put more glucose transporters in their membrane, they can. Uptake more glucose. And that's stimulated by growth hormone, also, amino acid uptake is increased by a similar mechanism and in conjunction with the increased amount of ATP from all the glucose uptake. The amino acids can be strummed together into proteins, and so overall growth hormone is going to increase protein synthesis all over the body, but especially in skeletal muscles. OK, so hopefully that makes sense. Let's take a look at bones growth hormone also is going to have similar effects on bones. First of all, growth hormones. And stimulate increased glucose uptake into the bone cell. It's going to stimulate increased amino acid uptake into the bone cells and again with that increased uptake of amino acids in conjunction with increased ATP synthesis, you're going to be able to synthesize more proteins. So protein synthesis increases. We're starting to see a trend with growth hormone. The other thing that we're also going to. See in bone. Is that we have an increase in bone mineral density. So the more growth hormone a person. Has the more dense their bones are, and this is important in preventing osteoporosis, one of the reasons why, as we age, we have an increased susceptibility to osteoporosis is because growth hormone levels naturally decline with age. And so if you have less growth hormone circulating in your blood at any given time, overtime your bone mineral density. May actually drop. OK, so increased bone marrow density. And then also during puberty, whenever your bones grow in length, remember that involves cartilage and the synthesis of cartilage is termed chondrogenesis. So growth hormone also stimulates chondrogenesis. Which helps bones grow in length. So overall, what the growth hormone is doing is through the adipose tissue in liver, it's increasing the amount of circulating nutrients and then those nutrients are taken up by cells like skeletal muscle and bone. Also growth hormone augments the uptake of those nutrients like glucose and amino acids. But then through metabolic pathways, we get more ATP and then we can build more proteins.

Speaker

OK.

Speaker 1

Now, growth hormone can also do two other things. One is growth hormone can actually stimulate the liver to generate another hormone that's released into the blood. And those are igfs or insulin like growth factors. One of the most common insulin growth factors is IGF one. Which would be term somatomedin 1. So igfs are also called somatomedin S. Those igfs travel in the blood to all sorts of peripheral tissues, and they exert functions there by binding to the insulin receptor and overall what the IGF's do is they increase glucose uptake by those cells. They also increase amino acid. Uptake and they. Increase protein synthesis. Really just as we saw. Over here in the case of skeletal muscle and bone, except it's not directly growth hormone that's doing that for a bunch of other cells. It's the IGF, the second thing that these do is they can actually exert negative feedback on the release of growth hormone releasing hormone. And So what they do is if there's too much IGF. In the blood. Those igfs can then circulate back and inhibit the release of growth hormone releasing hormone, because if we have plenty of igfs in the blood that signals that not only do we have plenty of igfs, we have plenty of growth hormone and we don't need to get anymore growth hormone released so IGF's can inhibit. The release of GHRH. It's also worth noting that there's another inhibitory hormone called growth hormone inhibiting hormone or HGH. IH and this can also exert a similar effect to IGF. It will actually inhibit the release of growth hormone OK. So hopefully this video gave you. A good comprehensive look at what? Perform on this. Doing like I mentioned at the beginning of the video, it's really just making sure that the blood has plenty of circulating nutrients and then it will also increase the the ability of a lot of these cells to uptake those nutrients, which then allows them to make more ATP and have more protein synthesis. And then, of course, growth hormone also stimulates the liver to release insulin like growth factors, which have similar effects on all sorts of other cell types. Now this is a really important topic to understand for growth hormone because in the next video when we cover the functions of thyroid hormones, what we're going to see is actually that they are very similar in function, very, very similar. There's a couple differences between the functions, but we'll cover those when we look at the thyroid hormones in. The next video so. Please make sure to like this video and subscribe to my channel for future videos and notifications. Thank you very much.

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