In this video, we're going to examine the main components of the dermis. The dermis primarily consists of a strong and very flexible connective tissue, but there are a lot of cellular elements within the dermis as well. You have fibroblasts that allow you to maintain the dermis.
You have macrophages and mast cells. Mast cells especially are very important in the inflammatory response. because they have the signal molecule histamine associated with it.
And there are several other types of white blood cells in the dermis. Moreover, the fibers that are found in the connective tissue in the dermis provide a matrix that holds the dermis to the epidermis and the dermis to the hypodermis. And it is this matrix that corresponds to the hide that we see.
when individuals make leather from animal hide. Additionally, you have nerve fibers, you have a lot of vasculature here, so there's blood vessels, lymphatic vessels. This is where hair follicles originate.
You have sweat glands, you have sebaceous or oil glands here as well. So when we look at the layered composition of the dermis, there are two main layers. So just deep to the stratum basale, you have the papillary layer. So above this green line is the stratum basale.
So these are my cuboidal cells that make up the stratum basale. And then underneath here is the papillary layer. Below this, so more deep to that is the reticular layer. So let's look at these two layers in a little bit more detail.
So the papillary layer consists of areolar connective tissue. So it's a looser connective tissue. It has collagen, it has elastic fibers, and I've already mentioned the blood vessels. Additionally, when you look at the papillary layer, it has these finger-like projection.
So I'm going to highlight it over here. You see this finger-like projection going in, and then sometimes another finger-like projection over here. These finger-like projections are known as the dermal papillae, the dermal papillae.
And sometimes within these dermal papillae, excuse me, dermal papillae, You will have some capillary loops, and we'll show you some examples of those capillary loops in a later video discussing thermal regulation. Within the dermal papillae, you have a special type of cell called the Meissner's corpuscle. Corpuscle is just a fancy term for cell, and like the Merkel cells, which were tactile cells, they were also touch receptors. But there are some subtle differences.
While the Merkel cells usually respond to sustained pressure, the Meissner's corpuscles are more like the touch receptors that you would activate if you ran your finger along your arm. So it's sensitive to very rapid signals. low frequency signals. So there are subtle differences in these two different types of touch receptors.
Additionally, within the dermal papillae, you will have free nerve endings that, if stimulated, can generate the pain signal. So there are pain receptors. And then in the thick skin, specifically the thick skin of the palms and the fingertips, you have dermal ridges.
So what are these dermal ridges? What are epidermal ridges? Well, when you looked at the dermal papillae, and I'm going to try to pick a different color here.
So in green, we had little finger like projection. But conversely, the stratum basale kind of goes in like that. So you have a little finger like projection here.
So what's shown here in red, that is the epidermal ridge. And what is shown In green, the dermal papillae is the dermal ridge. So cumulatively, this can form a very unique pattern as we develop from an embryonic state, and it is this that is responsible for the fingerprints that an individual has.
So this increase in surface area Between the epidermis and the dermis allows for a higher rate of nutrient exchange. Because remember, the dermis is what has the blood supply. The epidermis does not have any blood vessels.
In addition... These dermal ridges or fingerprints provide enhanced gripping ability because it increases the friction between the fingertip and the object that you are trying to hold. So the second layer is the reticular layer.
And the reticular layer comprises about 80% of the dermis. And while you have loose connective tissue for the papillary layer, in the reticular layer, it's a little bit more dense fibrous connective tissues. You have collagen, collagen that can actually go into the hypodermis and into the stratum basale to sort of unify and strengthen the connection between the layers.
So this provides added resiliency in the skin, and moreover, the collagen allows you to bind water, so it keeps the skin hydrated. Now, of course, as we age, there's a loss of hydration, and this could be supplanted with various moisturizers and various additives. So in addition to the collagen, you have elastic fiber, so it allows the underlying skin to stretch. Now what's really interesting, going back to the collagen that is found in the reticular layer, the collagen actually runs in parallel lines.
And so we call these parallel lines cleavage lines. Now, externally, the cleavage lines are not visible. So these are not visible like fingerprints are visible. This is specifically within the reticular layer. The significance of these cleavage lines, however, has to do with healing, with wound healing.
So in this particular image, let's say if I was to make an incision, In the thorax, I would make an incision from right to left or left to right, in between those cleavage lines. This is going to create less of a gap, and that wound will heal much faster. If I had made the incision this way, I'm disrupting multiple... collagen fibers and this would create a significantly larger gap and it would not as readily heal. So understanding the organization of these cleavage lines is very important for surgeons.