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.