Hormonal regulation of metabolism
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Hormone control of hunger
- [Voiceover] Let me ask you a question. Does this gentleman here look hungry or full? Well, we can't really tell just by looking at his face. We'd have to look at the level of hormones in his bloodstream, because depending on whether this person just ate or not, you'll have a change in the level of hormones that'll then talk to your brain to tell you whether you should eat more food or if you're full. The part of your brain that determines whether you're hungry or not is called the hypothalamus, the hypothalamus. Your hypothalamus helps make the distinction if your body is rich in energy or if your body is poor in energy. Or, in other words, are you hungry or are you full? Well, imagine we just ate, and the amount of glucose in our blood, or the serum or blood concentration of glucose is high. That means we're going to release a hormone called insulin. Insulin is released to store the glucose you have in your blood from whatever meal you just ate, and it'll go and bind receptors in the hypothalamus and block these receptors to indicate to the brain and the hypothalamus that you're full, you're not hungry. Now on the flip side, if you have a low blood concentration of glucose, you're not going to be releasing insulin, and so, you're not going to be inhibiting the hypothalamus. Now what if we ate a really fatty meal, and we have high levels of lipids or fat in our bloodstream? Something really greasy. Well, that'll cause the release of a hormone called leptin. Leptin is similar to insulin in that it represents the presence of energy-rich nutrients in the bloodstream. So it'll go to the hypothalamus and bind receptors there to inhibit the feeling of hunger, which means that when lipid concentration is low, you're not going to be releasing leptin, and you're not going to be inhibiting the hypothalamus. Now the final thing that talks to our brain is our stomachs. After we've eaten a bunch, our stomach will be pretty full with food, however, if we haven't eaten in a while, our stomachs can be pretty empty. And I'm sure you've had this happen to you. If you're stomach is empty, it starts talking to you. It starts making noises. It actually starts to growl, and if you listen closely, the stomach is actually saying, ghrelin, ghrelin, which just happens to be the name of the hormone that's released into the bloodstream to tell the hypothalamus that we are pretty hungry. We've got a pretty empty stomach. And instead of a bar, I'll put a plus sign here to show that the presence of ghrelin will tell the hypothalamus that we're hungry and motivate us to find some food. These three hormones, insulin, leptin, and ghrelin are the main players that determine whether we're hungry. One of the interesting things that I should mention, though, about leptin, which I can probably write here, leptin levels rarely change, and the reason why is because leptin levels are based more on the amount of adipose in your body than the amount of lipid you have in your blood, which makes sense because even though we'll eat some fatty, greasy meal that'll release lipids into our bloodstream, we'll definitely have a lot more fat tissue in our body beforehand. So any change in lipid concentration in the blood will be very small relative to how much fat or adipose tissue we have stored in our body.