 Look at this picture, it kind of trips me out when I look at it, but this is what's happening to your body every second of every day. It is so easy to be dead and so hard to be alive, right? Think about all the things that can go wrong in your body that can be fatal, right? It is so easy to be dead and not need countless numbers of chemical reactions and not need perfect balance between every cell, tissue, organ system in your body, right? So if you look at your body right now, you are alive and hopefully you're well and disease-free because your body is able to balance you on this razor's edge of improbability, right? If your temperature goes too low, you die. If your temperature goes too high, you die. If your pH goes too low, you die. If your pH goes too high, you die. Blood calcium levels go too high, you die. Blood calcium levels go too low, you die, et cetera, et cetera. Think about all the things that have to happen to keep you alive. Or like in your clinical classes, if you ever look at your lab values, you've got that normal range. As long as everything stays in the normal range, you should be good, right? But if you have the low range and the high range, if you see that, it's because someone's body is having trouble maintaining this homeostasis. So just keep that in mind that your body is unbelievable, the countless, I mean the quintillions of things it's having to do to keep you alive every moment. It is truly something to marvel at. All right, let's go ahead and talk, let's get away from that image. It's making me a little dizzy. Let's talk about homeostasis. So the most important term in anatomy and physiology is homeostasis. My job is to teach you the structures and functions that maintain it. So what is homeostasis? The word means staying the same. How we define it is the maintenance of a stable internal environment. No matter what's going on outside of your body, you should be able to maintain a stable internal environment. And so this is a class where I teach you normal. You'll go on and take your pathology classes and clinical classes later where you'll learn, and we use examples in this class too, but you're going to learn what happens when your body can no longer maintain homeostasis. So if you stay in a state of homeostasis in every conceivable way, then you're healthy, then you're well. But once your body cannot control something and keep it in a normal range, you now have a disease. So your body has systems that lower and raise blood pressure, for example. But if your blood pressure gets too low and your body can't prop it up, you now have hypotension. If your blood pressure gets too high and your body can't bring it down, you now have hypertension. For most people, we can control our blood sugar, but for about 100 million Americans, they're either diabetic or pre-diabetic. That means that their blood sugar is climbing too high. Their body can't bring it back down like it should, and they now have hyperglycemia. But some people, their blood sugar gets too low and their body can't keep it up. They have hypoglycemia. Those are just a couple of examples. But what's really cool about homeostasis is we can maintain a stable internal environment even when our environment changes. As you go outside, it's negative 20 degrees. Your body can keep your core temperature normal. It's 120 degrees. Your body can still keep your core temperature normal. All right. So these are just countless numbers of things. We're going to learn all this stuff throughout the year, the types of things that have to stay in normal ranges. Blood cell counts, the electrolytes in your blood, et cetera, et cetera. So many cool things. All right. Let's look at... So this is a tip of what homeostasis has built around these three pieces. I'll do a separate video where I cover the two types of feedback, negative and positive feedback. So to have a homeostatic regulatory mechanism that helps you maintain a stable internal environment, you need these three parts. A sensor, which responds to the world around you. We're going to cover all sorts of sensors and receptors. The control center, which is often the brain, but can also be the spinal cord. And there's even local control mechanisms. And then the effector. So the sensor says something's wrong. The control center says, here's how we fix it. The effector goes and fixes it. So the effector is going to be that whatever responds. So I won't give you an example. Now this video is getting kind of long, and I'll give you a ton of examples in the next video where we cover negative feedback loops. So I think I'll stop right there because I want to tell you what negative feedback does so bad, but just click on the next video. Okay. I hope this helps. Have a wonderful day. Be blessed.