字幕表 動画を再生する 英語字幕をプリント The human body is amazing, a symphony of bones, muscles, cells, organs, liquids and an incomprehensible number of chemical reactions, all working together simultaneously to keep us moving, breathing and well living. And we think learning about all these details, big and small, is fascinating. So we put together this new series for you. We’re calling it Human, a learning playlist dedicated to everything that makes us us, covering all the basics of anatomy and physiology that we could fit into one playlist. Now, even though we can’t teach you everything about the body in just a few videos, the goal is to teach you enough core concepts so that you can feel more informed when reading news in your social feed, talking to your doctors or even sitting down to take your midterms. Because the cool thing about studying the human body is that everyone has one, so it’s relevant to literally everyone. Unless you’re a ghost. In that case, I guess not. If you are a ghost, let us know in the comments. My name is Patrick and I’m going to be your host for this series. I studied multiple branches of science having to do with the human body before becoming a teacher and science writer, so I’m very excited to nerd out about the body with you. We’ll talk about blood and the immune system and hormones and stem cells, just to name a few of the topics. Plus, there’s so much cool research happening right now that uses these basic concepts, and we’ll talk about that, too. Before we get too into the weeds of any one topic, we’re going to need some background info. There are multiple branches of science dedicated to studying something about the body — but a lot of them focus on what happens when things go wrong. Studying disease is interesting, but we’ve already got an entire separate series for that called Sick which you can go watch. In this series, we’ll focus on anatomy, or the study of shape and stuff of the body, and physiology, the study of all the processes that happen within it. Anatomy is form, physiology is function. And form influences function at very small and very big levels. To see how, it’s helpful to organize all of biology into a hierarchy in something called biological organization. It’s a useful way of organizing tiny things like cells into larger groups, but it also lets us picture bigger things like bodies as a collection of organ systems. Over the course of this video, we’ll take a look at the integumentary system because it provides a great example of this hierarchy. To start with, we’re all made of matter at the most basic level. This includes all the atoms and molecules that combine together to make the membranes of our cells, the salt in our sweat, or the neurotransmitters that travel between neurons. And when we parse all the matter that makes up skin, we find all kinds of lipids, minerals and proteins that assemble into the structures that make your skin tough but flexible. And water. We’ve got so much water in our bodies. Those chemicals combine to form the different parts of cells, the smallest living thing on the hierarchy. Literally the smallest unit you can point to and say “this is alive”. Now, there are a few generally agreed upon criteria on what it means to be alive: the thing needs to be able to reproduce, grow, respond to its environment, use energy, have some kind of organization to its body, and maintain an internal balance called homeostasis. It doesn’t matter if we’re talking about a skin cell or muscle cell or a single celled organism like an amoeba. To be considered alive, you need to meet those qualifications for life. And even at this tiny cellular level, we can see form influence function first hand. Again, take our skin example — it has multiple types of cells, but they all serve different purposes. Check this out. All those hairs sticking out of your arms, eyebrows, or nose, are made by specialized cells called keratinocytes, cells that crank out the keratin that forms hair. And your skin’s color comes from the pigment melanin, made by other specialized cells called melanocytes. But the real stars of the integumentary system are the layers of epithelial cells, a cell type that comes together to form tough yet dynamic borders between what’s inside or outside of your body. Those keratinocytes in your skin? They’re a type of epithelial cell. But if you could take a Q-tip and grab some cells from the lining of your stomach, those are also epithelial cells. This is where we see form influence function again. Epithelial cells typically make up borders or walls, protecting us from different types of harm like radiation, chemicals, or bacteria. And just like building a physical wall, multiple layers of material tend to be stronger than a single layer. And when any type of cell, epithelial or not, groups together like this to do a common job, they form the next unit on the hierarchy chart: tissues. There are four main types of tissue: epithelial tissue like your skin, muscle tissue in your heart and skeletal muscles, connective tissue like your ligaments, and nervous tissue like, you guessed it, your nerves. We’ll go into specific types of tissues in later episodes, but for now, start thinking about tissues as groups of cells. Now, clearly with multiple types of cells we can get multiple types of tissues. And when different tissues combine to do a common job, you get organs, the next step on the hierarchy. You’re familiar with some of the big internal organs: liver, kidneys, intestines. But the skin, the example we’ve been using, is itself an organ. Because it’s not just a protective layer. Like those other organs, it has different tissues combining to do one job. The epidermis is the outermost layer, that physical wall we mentioned before. But underneath that is the dermis, where you’ll find the tougher connective tissue to make your skin even stronger, but also more specialized tissues like nerves, sweat glands, and hair follicles. Even deeper than that you’ll find the hypodermis layer which stores a little bit of fat. So, even though it looks pretty similar from your head to your toes, it features multiple tissue types to function as a dynamic organ. And when organs work together with other organs, they form organ systems, which are exactly what they sound like, functionally similar organs that have a common job. Like how your integumentary system is so much more than just skin. It’s also the glands, nerves, fat and muscles under the skin that you don’t see. Working together, this is one of the systems that helps keep your body in a livable temperature, protects your squishier internals from harm, and helps us interact with the world via touch. Now, that means at some point our integumentary system needs to talk to our nervous system to interpret all of those signals. But in reality, every system interacts with every other system in your body to, you know, stay alive. Like our endocrine system, or hormones, works closely with our reproductive systems, and our digestive system works closely with our urinary system to get rid of waste. That’s like the number one thing it does. Either way, all of your organ systems get wrapped up into one, unique individual body, or organism, the last unit on our hierarchy. At this point, we’re talking about bodies that can eat tacos, and pet puppies, and binge watch the entire Lord of the Rings trilogy all at the same time. Not that I have. Just saying you could. Thanks so much for watching this episode of Seeker Human. We’re going to be talking about a lot of cool stuff this series so make sure to keep coming back to Seeker, we’ll see you next time.