Hi. It's Mr. Andersen and in this video I'm going to talk about the integumentary system,
which is skin. But it's also hair and nails. And what that does is offer us protection.
In other animals it would be made up of scales or in birds it's feathers. But it has not
only protection as one of its functions and that's important. It keeps bacteria out, foreign
objects outside our body. It also allows us sensations so we have tactile receptors deep
in the skin that will allow us to sense touch and pain. It also allows us to thermoregulate.
And so not only goosebumps but we can vasodilate and move blood near the surface. And that
carries heat away. We could also have sweat glands that pump sweat out. And so that, as
it evaporates carries heat away. And so it's important in thermoregulation and it's also
important in allowing sunlight in. And so we need sunlight to synthesize vitamin D.
If we don't get vitamin D then we can't bring phosphorus and calcium into the bones and
so we develop a disease called rickets. And so those four things are super important in
the integumentary system. But the whole thing revolves around the largest organ in your
body which is going to be the skin. The top layer of skin is called the epidermis. And
if you get a tattoo we have to make sure that we're putting that ink underneath the epidermis.
If we didn't it would just simply be lost over time. Now the epidermis itself is made
up of four individual stratum which are going to be layers of cells. And if we start at
the bottom we have the stratum basale. That stratum basale is going to be kind of convoluted
over space. And so if you look along the bottom it forms what are called the dermal papilla.
And the function of that is it holds the epidermis on the dermis which is below it. Another important
role of the stratum basale is that it's where mitosis occurs. And so we're creating new
cells on the bottom. And then those new cells are migrating up and eventually we have dead
cells up on the top. And so that's where those new cells are being created over time. On
top of that we have a stratum spinosum. And it gets its name from the spiny appearance
it has when you were to dye it with specific dyes. What's the function of that? Well we
need to dig down a little bit deeper. And so if we were to look at the cells down in
that basale layer and then in the spinosum layer up above it, well there's a couple of
things that are going on. Number one we have these melanocytes down at the bottom. And
so what's that giving us? Well it's giving up melanosomes, which are organelles which
give off melanin. And so that's going to give us different colors in skin. And so dark colored
skin is going to have more of these melanosomes and more the the melanin then light colored
skin. And so that's that balance remember. If your ancestors grew up around the equator
it was important to have more melanin because we could start to develop cancer and decrease
of folic acid. And so birth rates went way down. But as you move to the north, the reason
I am so light in color is that my ancestors needed to have low amounts of melanin so I
could synthesize vitamin D. So as we keep moving our way up we eventually get to the
granulosum, stratum granulosum and it's granular in appearance because everything is kind of
getting compressed. Now how are nutrients getting up here? Since there's no capillaries
up in this upper layer of the epidermis, basically it's diffusion. And so these cells are essentially
dying as we move up. Next layer is not going to be found in all skin. That's called the
stratum lucidum. And so in certain skin, we call that thin skin, you'll only have four
layers. But in the thick skin you'll have this additional stratum lucidum. So what's
the skin that's so thick? That's going to be in our palms and also on the soles of our
feet. It offers us more protection. And then we finally go up to the top. We have stratum
corneum. And that's going to be these dead cells. And eventually those leave us, but
they're replaced from cells right below it. Now that's a lot of stratum. How do you remember
it? Here's a quick mnemonic. Come, let's get sun burned, is a quick way that you could
write those letters down if you're taking a test. And then you could go through all
the different parts. So the "b" stands for the basale, spinosum, granulosum, lucidum
and then finally the corium up on the top. Now that's just the epidermis. What's below
that? We have the dermis. And the first thing that's going to jump out is the vascular tissue.
So we're going to have capillaries that reach into the dermis. And so blood is making its
way inside there. Nourishment is making its way into the dermis. What are some other things
that jump out right away? We're going to have big glands here so this would be a sweat gland.
This would be a sebaceous gland. That's going to essentially release oil which is going
to keep our hair waterproof. And it's also going to keep our skin waterproof over time.
As we look deeper we find these receptors. And there's lots of different receptors. So
this yellow right here would be nerves, but we have all these receptors that are sensing
our environment. Ones near the top are sensing light touch. And the ones farther down are
sensing deep touch. We also have pain receptors in the skin at this point. It keeps us from
damaging our skin. As we move farther down we have the hypodermis, which is sometimes
referred to as the subcutaneous. And as we move down in here there's going to be a lot
of connective tissue in here. And so we're going to have these fat cells. We're also
going to have some stem cells that are creating other cells. We're going to have macrophages
that are cruising around. We're going to have lots of fibers, like reticular strong fibers.
And then this elastic fiber, so when you pull up your skin it just bounces back to where
it was below before. And so that's the hypodermis. And then we have these accessory structures.
The big ones are going to be hair and then nails. And so if we look at a hair follicle
right here, way down at the bottom we start to have capillaries coming in. So this is
going to be vascular tissue down here on the papilla. Above that we have what's called
the matrix. That's going to be one layer of cells that constantly are making new cells.
The cells as they're pushed up are forming the hair. And so the hair is basically made
of dead cells. And there's tons of keratin in there. Keratin is what our fingernails
are made up of and it really makes that durable hair. But as we move up here now the cells
are dead. And it's eventually going to move up past a sebaceous gland. Remember that's
secreting oil, which is delivered on to the skin. And it's also delivered on to hair making
it somewhat waterproof. And then we could look at the nails. So the nail is going to
be made essentially in the same way. We have a matrix down at the bottom. And so this pink
right here would be the epidermis. But then it dives down into the dermis. And so the
nail itself is being created by cells that are quickly dying. They're filled with keratin.
Then we have the eponychium up on top of that. That essentially makes the cuticle. You could
kind of see it right here. And then we're going to have a lot of vascular tissue up
here. But not so much right down at the bottom. And so that's going to be the nails. Where
did they come from? They were claws in a lot of organisms. And they allow us to kind of
deal with tools. And so if we were to go through the review, can you remember the three different
layers of skin? Remember at the top that's going to be the epidermis followed by the
dermis and then the hypodermis. Do you remember the four layers of the epidermis? So, come
let's get sun burned, allows us to remember that at the bottom the "b" stands for basale.
The "s" stands for spinosum. The "g" stands for granulosum. And we've got the lucidum.
Remember that's only going to be found in the the thick skin. And then on the top we
have that stratum corneum which is going to be the upper layer of our skin. And we've
also got the hair and the nails. But that's the integumentary system. It's got four-fold
importance. And I hope that was helpful.