Mind that the previous two videos were about the epidermis. Now I'm starting a new video on purpose to make sure that you understand the separation between the epidermis, the cells of the epidermis, the layers of the epidermis, and then this new topic, which is the dermis. There are two layers to the dermis. Going back to this picture, there's oftentimes in anatomy and physiology, there will be a picture early on in the chapter that gives you a lot of details about things that you need to know. This is actually a really good picture to keep going back to for a number of different reasons.
Now we just discussed the epidermis, which when you put it in perspective, you'll start to understand that it's actually a very, very small part of your skin. It's just the very most upper layer in here. Your dermis is between 0.2 millimeters thick and 4 millimeters thick.
Again, it is leathery. It is leather. If you have a leather jacket. That is the dermis and here's the dermis. It's this pink stuff between here and here between the epidermis and the hypodermis.
So this is the bulk of your skin. Okay, so in the dermis, although they are not very well delineated in this particular picture, if you look closely, there's a few clues in here that show you two different layers. First of all, they're labeled.
But second of all, you'll start to see subtle differences between the most superficial layer, which is quite thin, the most superficial layer of the dermis, and then the thicker, deeper layer of the dermis. So as you can see here, the labeling right here at the very superficial most part of the dermis is called the papillary layer. The papillary layer is made of a connective tissue that's called areolar connective tissue.
The areolar connective tissue is primarily comprised of collagen fibers and elastin fibers. which means collagen means strength and elastin means stretchability. There are many blood vessels in this region as well. Now you will see dermal ridges.
You'll see this kind of invagination that kind of dips into the epidermis, and that is why this layer is called the papillary layer. The root papilla you'll be coming across more in future. Papilla means nipple-like. projection.
So anytime you see little dips that look like kind of little nipples, that is oftentimes called papillary or papillary something. So this is a papillary layer of the dermis. The papillary layer is much more pronounced in areas like the palms of the hand and the soles of the feet.
And in these areas, these invaginations are called dermal ridges, and these will increase your friction. and enhance your grip. Perhaps you can derive what dermal ridges are.
The deeper layer of the dermis then is called the reticular layer. The reticular layer takes up 80% of the thickness of your dermis. It is made of dense irregular connective tissue. Now dense irregular connective tissue does have a little bit of elastin in it, but it is primarily comprised of collagen fibers that are sort of arranged almost haphazardly with each other. And the beauty of dense irregular connective tissue is that it is very, very strong, very tough, and it really resists tearing in various directions.
So you can try all you want to tear a leather jacket. You're not going to be able to do it because the dermis is simply very, very tough. At the same time, it is very flexible. So it's a really cool material. Okay.
That's what I wanted to say about the dermis. And of course, that's what I wanted to say about the layers of the dermis. Of course, you can notice that there are going to be a number of different accessory structures that are buried in the dermis. You can see hairs buried in here, so you'll see the root of hairs in here. You'll see various glands.
Now, I'm going to cover these in a little more detail in the next video. But here you see the roots of hairs. You see glands.
You can see there are some specialized muscles here. And you can see little nerves running through. glands again, muscles, nerves, so you start to see a lot of really interesting stuff going on in the dermis that you don't actually seem to find in the epidermis. So as far as the three layers of the skin, I would say that the dermis is the most interesting.
One of the things you'll notice, and this is going to come up again, is the blood vessels, the vasculature. Note that there are blood vessels down here at the bottom, at the most deep part of the dermis, deep inside the reticular layer. And, it's a little subtle, but you'll notice that there are blood vessels that make their way throughout the papillary layer as well.
A real or connective tissue of which the papillary layer is comprised is kind of famous for being very vascular, so you'll find blood vessels in the papillary layer as well. Note though, that you actually don't see a lot of vasculature through the bulk of the dermis. Dense irregular connective tissue does not tend to be very vascular.
It's very tough, it's very flexible, but it is not very vascular. There's not a lot of blood vessels in there. So you'll see the blood vessels up at the surface. Deeper down below, but not a lot in between.
Just keep that fact in mind for when we talk about body temperature regulation.