about something called the integumentary system.

"And what does that mean?

"I mean, I can understand what the cardiovascular system is,

"or the pulmonic system or the renal system,

"but what is your integument?"

What comprises the integumentary system?

And there are actually two things we talk about.

The integumentary system is comprised of your skin

as well as your appendages.

Now, "appendage," what does that sound like to you?

An appendage could be something that hangs off,

or something that's a part of, like your arm is a part

of your torso.

Well, the appendages

of your integumentary system involve things like your nails

on your fingers and on your toes, your hair on the top

of your head or on your arm or elsewhere,

and also things like your sweat glands.

Glands in general kinda fall under this classification,

and we'll talk in detail about these appendages later,

but I wanna focus on the skin right now

and do a bit of an overview.

Because whether you recognize it or not,

the skin is actually the largest organ in, or on, your body.

It's 21 pounds.

That's far heavier than your liver or your lungs,

and yet, many of us can go an entire day without thinking

about the functions of our skin.

But what are the functions of our skin?

If I told you this was your arm right here,

and this is you giving a little thumbs up,

and then your fist, and then this going back here,

what is it that the skin on your arm enables you to do?

Well, one thing you may have noticed is

that when it's raining outside,

and you've got raindrops dropping on your head,

one thing your skin enables you to do is be impermeable

to the water.

It's impermeable to water and other things that try

and breach its layers and go into your organs

or your bloodstream.

It's impermeable, it cannot be passed, and that's as true

for water and other molecules like this virus right here,

which I'm drawing.

Here's this little capsid and its little legs.

It wants to come and infect the cells of your body,

but thankfully your skin says no to this virus,

and it's not allowed to enter or breach this barrier,

because it's impermeable.

But it's not just a structural barrier,

it also has an immunologic function as well.

Your skin can secrete things like antibodies,

or even enzymes like lysozymes.

These are the guys that'll go and take on these viruses.

Or say if there's a bacterium that's present

that has intentions of also getting you sick,

the antibodies can coat this sucker right here,

and the lysozyme can assist in breaking

down the cell wall to help protect your skin.

And so, your skin also functions as part

of the immune system.

So immunity is also in play here, not just what

this antibody or this lysozyme...

Perhaps you can imagine a scenario where the bacterium

even penetrates a few layers of your skin,

and thinks that it has an opportunity to set up shop,

or make an infection or an abscess somewhere.

But you have cells that are within your top layers

of skin, like your Langerhans cells, like we'll talk about,

that'll eat these bacteria up and prevent them

from setting up shop or making you sicker

than you should be.

Other than immunity, your skin can also perceive things

in the environment.

If I have this little pin from a pin cushion

that I can prick right here,

and it really hurts right there,

your skin will tell your brain,

"Hey, maybe we shouldn't put our hand so close

to this sharp object."

So, your skin also has the responsibility

of perceiving your environment,

and so it conducts sensation.

It's able to tell when there's a stimulus

that's either painful, so it perceives pain.

It can tell different temperatures,

whether something is hot or it's cold.

And also, it can differentiate types of touch

that are present, and discriminate between textures,

whether something is just grazing your hand

or something is poking you deeply.

And finally, when you're outside and it's really hot,

just kind of as I was already alluding to with the ability

to perceive temperature, your skin has the ability

to respond in a process that's called sweating,

as we know it.

We sweat because of our skin, and the glands in our skin,

and it's all part of an overall process known

as thermoregulation, because our sweat allows us

to cool off by a process known as evaporative cooling.

But there are also processes that involve our blood vessels.

Here's a blood vessel in your arm right here

that can help us conduct heat out of the body.

Let's get rid of that heat,

because we notice it's already hot outside.

So the skin is so much more than just a barrier,

there's a lot that it does for us.

And in the next few videos, we'll go into detail

about how all of these functions are achieved.