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 sensation. So we have tactile receptors deep in the skin that allow us to sense touch and pain.
It also allows us to thermoregulate. And so not only goosebumps but we can vasodilate, 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 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 layers. stratum, which are going to be layers of cells. And if we start at the bottom we have the stratum basal.
That stratum basal is going to be kind of convoluted over time or 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 basal is that it is where mitosis occurs.
And so we are 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 the 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 basal 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 then we have these melanocytes And so what's that giving us? Well it's giving us 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 of the melanin than 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 it decreased folic acid. And so birth rates went way down.
But as you move to the north, the reason I'm 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. The 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 only have four layers. But in 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 sunburned 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 basal, spinosum, granulosum, lucidum and then finally the corneum 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 onto the skin. And it's also delivered onto hair making it somewhat waterproof. And then we could look at the nail. 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 then we have the dermis.
And then we have And so the nail itself is being created by cells that are quickly dying. They're filled with keratin. Then we have the epinysium 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. 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 cum, let's get sunburned, allows us to remember that at the bottom the B stands for basal. The S stands for spinosum. The G stands for granulosum. Then we've got the lucidum.
Remember that's only going to be found in the thick skin. And then on the top we have that stratum corneum which is going to be the upper layer of our skin. 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.