In this video we are going to discuss the skin.
The skin also known as the integumentary system.
The first thing you need to realize is that we actually have two varieties of skin.
We have what is called thin skin and thick skin.
Obviously on this end of the model we can see the skin is much thicker, and we will
talk about the different layers of the thick skin in just a moment.
Now all skin is made up of an external layer known as the epidermis.
And in this model everything in the purple on out is epidermis.
The remainder of the skin is the dermis.
And then under the dermis we have what is called the sub dermis or the hypodermis.
Now on this model we can actually see three varieties of skin.
We can see the skin of the hairy scalp.
We can see the skin of the axilla, or the armpit.
And then we can see thick skin.
Thick skin is found on the palms of the hand and the soles of the feet.
Notice thick skin does not have hair.
It can have hair but rarely does it have hair.
Also in this model we will see that there are different glands associated with the skin.
In the skin of the scalp and in the skin of the axilla, the armpit, and in the skin of
the palms and the soles we see eccrine sweat glands.
On this model these are the white, coiled glands with a simple duct leading to the surface.
Eccrine sweat glands make the sweat that we find all over our body.
In the axillary area, also in the ano-genital area, we see another form of sweat gland known
as the apocrine sweat gland.
Sweat from apocrine sweat glands is very similar to that from the eccrine sweat glands, however
this sweat has more fatty substances and more proteins involved.
This is why if you do not wash the sweat in the axillary area within a few days bacteria
will begin to live on those proteins and fatty substances and you will begin to exhibit a
particular order.
We also can see that the hair goes down into the dermis of this tissue, where we have the
root ball and the hair root follicle.
Along with that root follicle we have a small muscle known as the arrector pili muscle.
Also associated with the hair we will see sebaceous glands.
Sebaceous glands make oil that is secreted along the shaft of the hair.
This is what gives our hair an oily appearance if we don't wash our hair.
So we have here skin of the scalp.
How can I tell?
I see that we do not have any apocrine sweat glands.
We have eccrine sweat glands.
Clearly we have hair, and we have the thin skin variety.
More about that in a moment.
This is skin of the axillary region.
The reason I can tell, we have the hair, we have the eccrine sweat glands, but we also
have the apocrine sweat glands.
This is skin of the palms and the soles, also known as thick skin.
I can tell for a couple of different reasons.
It is hairless.
And when we zoom in on this area, which we will do in just a moment, we will look at
some of the different features of thick skin versus thin skin.
Another structure that we can see in this model, they only depict it here in the thick
skin but it is does occur in all areas of the skin, deep in the dermis right at the
area between the dermis and the hypodermis we have a, kind of a laminated or layered
structure known as a Pacinian corpuscle.
This Pacinian corpuscle is responsible for detecting pressure that is put on the skin.
Notice it is located deep within the skin so it would in fact take pressure pushing
on the skin to activate the different layers to send a nerve impulse from this Pacinian
corpuscle.
If we look carefully in this small region here of the thick skin we can also see that
if I peel off the epidermis I see little fingerlike projections leading out from the dermis.
These are called dermal papilla.
Dermal papilla have blood vessels and they have nerve endings.
In this particular case they show nerve endings with Meissner’s corpuscles up inside the
dermal papilla.
A Meissner’s corpuscle is for detecting fine touch.
This model does not depict, however if the nerve comes in to the dermal papilla and does
not have a specialized nerve ending, it is called a free nerve ending and those are for
sensing pain.
I want to take a closer look on this model at the area of the thick skin.
Although it applies across the entire model.
The first thing I want to do is take a look at just the dermis of the skin.
So on this end where we have the thick skin on the model we peeled off the layers of the
dermis, or the epidermis, all that is left is the dermis.
The top roughly 20% of the dermis is known as the papillary layer.
The remainder of the dermis is known as the reticular layer.
So notice that the eccrine sweat glands, the Pacinian corpuscles and the apocrine sweat
glands and the hair follicles and the arrector pili muscle are almost all associated with
the dermis.
And they are associated with the reticular layer of the dermis.
Blood vessels throughout the reticular layer and reaching up into the papillary layer of
the dermis.
Now if we focus in on just this area of the thick skin we can see that the dermis, or
the epidermis is actually divided into five different layers in thick skin.
In thin skin it is four layers.
But if we focus carefully we can see the very bottom layer of the epidermis is known as
the stratum basale.
The base layer.
That is made of different cell types which you will learn in lecture.
And those cell types divide and the keratinocytes of that lawyer give rise to the next layer
which is a lighter shade of purple in this particular model.
And that layer is known as the stratum spinosum.
Now as those cells get further and further and further from the stratum basale they begin
to die.
And in this model you can see here some small black dots.
Those are granules that are forming within those keratinocytes.
That layer is called the stratum granulosum.
The stratum granulosum.
Then we see on this model a yellow line.
This yellow line represents what is called the stratum lucidum.
The stratum lucidum is only found in thick skin.
It is not found in thin skin so if I compare this thick skin here with the thin skin next
to it I still see the stratum basale, the stratum spinosum, the stratum granulosum,
now I cannot see the stratum lucidum.
And then in the thin skin I have a very thin layer of the stratum corneum, whereas in the
thick skin and I have a very thick layer of stratum corneum.
So the five layers of thick skin, stratum basale, stratum spinosum, stratum granulosum,
stratum lucidum, and the stratum corneum.
Keep in mind thin skin the corneum is thinner and we do not have the stratum lucidum.