字幕表 動画を再生する 英語字幕をプリント What’s the first thing that comes to mind when I say the word hormone? Pimples? Mood swings? Cramps? Really inopportune moments where your armpits get sweaty? Are we good? We’re good. Hormones are obviously involved in puberty, but they’re so much more than that. Like hormones are involved in how we deal with stress, and in triggering our immune systems, and in steroids. So, grab your antiperspirant and acne cream, today we’re talking about hormones. In a previous episode you heard me talk about blood and all the stuff floating around in it. We talked about blood cells and glucose and different biomarkers, but I also mentioned chemicals called hormones. Now, I’m assuming that when I say the word hormones, you’ve already heard about testosterone and estrogen, but hormones are a much more diverse part of our physiology than just those two. Hormones are any number of chemical messengers that get secreted by glands, travel through the bloodstream, and have an effect on cells with receptors for that hormone all around the body. They’re like a long distance messaging service in one of our body’s systems called the endocrine system, a system for communicating messages across long distances in our bodies. And their effects are incredibly diverse as well. Hormones can stimulate growth, metabolism, immune function and much more. Some hormones even double, triple, or quadruple dip in the functions around your body. For example, thyroid hormone is important for development while you’re in utero, but also in maintaining metabolism in your adult body. At the same time, multiple hormones can team up to do the same job. Like controlling blood sugar largely depends on the hormone insulin which is made by your pancreas. But it also depends on hormones like glucagon, cortisol, epinephrine, and growth hormone. The point is, it’s really hard to imagine the endocrine system as a single cause and a single effect. Hormones are less linear, and more like a tangly web. That’s in part because this system is built off of feedback loops, mechanisms where changing one aspect of the loop can lead to increases or decreases of another depending on the situation. These feedback loops can be positive or negative, which doesn’t mean good or bad, just how a hormone is affected by some other substance. In a positive feedback loop, if you increase one factor, it also increases another which increases the original factor which keeps the loop going. To quote a late nineties chip advertisement, once you pop the fun don’t stop. Right, let’s take a look at childbirth. Now that I say that out loud I’m not sure it was the best transition line, but let’s roll with it. During childbirth, the size of the baby’s body applies pressure to the cervix it’s trying to pass through. This triggers the release of the hormone oxytocin which stimulates more cervical contractions which stimulates more oxytocin which stimulates more contractions and so on. We don’t use positive feedback loops as often as negative feedback loops since they can end up with hormone levels spiraling way past the normal, ideal value. But in this case, the feedback loop has a natural stopping point when the baby is born. Then afterwards, the oxytocin levels return to what they were before childbirth. Way more commonly, our hormones are regulated by negative feedback loops, where an increase in one substance eventually eventually leads to a decrease of that same substance. This makes sure hormone levels stay fairly consistent from day to day. For example, your body can sense when your blood is dehydrated and it’ll adjust some hormones so you can conserve as much water as possible. One of those involves increasing the release of vasopressin, a hormone released by the pituitary gland. This bump in vasopressin makes the kidneys more permeable to water by temporarily adding little water channels onto the surface of cells. This moves water back into the bloodstream towards a more normal value. And now that the blood is back to normal, the pituitary stops pumping out as much vasopressin. That’s what makes this a negative feedback loop. Vasopressin increased, it had its effect, so the body lowers its secretion. One of the other hormones that uses a negative feedback loop is cortisol, arguably one of the most important hormones, and an example of a steroid, which we’ll come back to. Cortisol is often called the stress hormone since it gets released during times of stress and gives our bodies resources for surviving the stressor like increasing sugar metabolism and buffing up our immune system. This hormone is constantly in the process of its feedback loop since, as you know from existing as a human in the modern world, life is stressful. So our bodies are constantly pumping out cortisol, which begs the question, how do we make a hormone? Well what they’re made of differs from hormone to hormone. Most are made of proteins, or peptides, some from phospholipids, while some are made out of cholesterol. And our buddy cortisol is made out of cholesterol. That’s part of what makes it a steroid, hence the “stero-” part of both words. In order for cholesterol to turn into any steroid, it goes through a transformation pathway .. It starts by converting into a molecule called pregnenolone. From there it can convert into progesterone, an important hormone in pregnancy and the ovulation cycle. Even if you personally don’t ovulate, progesterone still makes important compounds in your body. And with a few more chemical conversions it can turn into cortisol, or into androgens, which include testosterone or estrogen. Testosterone itself can then get converted into estradiol, a super common estrogen. By the way, that was so fascinating to me when I first learned it. When I was in primary school, I was taught that testosterone and estrogen were opposites, but in fact, they’re extremely similar chemically and get made from the same ingredients. So when we’re talking about steroids, we’re talking about hormones derived from cholesterol. But in everyday conversation, when people talk about steroids, they’re probably talking about anabolic steroids, hormones taken for the purpose of building big strong muscles. These work by slipping into muscle cells, and hooking up to an androgen receptor. This stimulates the cell to produce more proteins and thus bigger muscles. Now, just because these types of steroids have been abused in the past doesn’t mean that the broader class of steroid hormones themselves are harmful — in fact, doctors often prescribe steroids as a medication. Most of the time, these medications have nothing to do with muscle. Take a group of hormones called corticosteroids. The etymology gives this one away, but these are any steroids that resemble cortisol. These hormones have a /bunch/ of different effects from controlling the stress response to regulating our immune system. Now, I want to be super clear. Corticosteroids aren’t immune cells, they’re chemicals that can have an immune effect. What makes them so effective is their ability to switch off multiple genes involved in different aspects of inflammation. Let’s break that down. Inflammation is what happens when our bodies mount an immune response, and part of that is making certain proteins. These proteins aren’t just the ones that go into building muscles, but include enzymes for speeding up chemical reactions or different chemical messengers involved in recruiting immune cells. Now, our genes hold all the information needed to manufacture these proteins. And certain chemicals called transcription factors can get our cells to crank out more and more of those inflammatory proteins. So when corticosteroids are floating around in our blood and make their way into a cell, they start a process that inhibits the effect of those transcription factors that keep inflammation going. Plus in larger doses they can stimulate the production of anti-inflammatory proteins. And because of that, these steroids are also a useful treatment for reducing inflammation in conditions like arthritis or allergies. That long-acting asthma inhaler? Yep, that’s a steroid to reduce inflammation in your lungs. One of their other biggest use cases is acting as an immunosuppressant, literally a drug that intentionally weakens your immune system. Wait, why would you weaken your immune system on purpose? Well, most of the time the immune system is good at identifying the things we don’t want in our bodies and getting rid of them. But sometimes, our immune systems turn on us and attack our own tissues. For instance, if you watched our other series Sick, you’ve heard us talk about lupus, an autoimmune disease that can cause inflammation. One of the consequences of that disease could be kidney inflammation, and if it gets bad enough it might lead to kidney failure, which is lethal. The steroid comes in handy by slowing down the production of chemicals that lead to inflammation, and by tweaking how white blood cells work. A doctor might prescribe an immunosuppressant steroid to someone with lupus to reduce inflammation and save their kidney and thus life. So it’s a trade off. Increase your risk of infections from the outside world but save yourself from your own body. You might also need to weaken your immune system after getting an organ transplant. According to your body, that new organ is a foreign object and shouldn’t be there. We’ll learn all about how different cells in the body communicate with each other, including some of those immune cells, in the next episode. Thanks for watching Human on Seeker. I'm Patrick Kelly.