The epidermis is made up
of four different types of cells.
The first type of cell is an
epithelial cell known as keratinocytes
This creates a keratin layer which is very strong
intermediate filament found inside of these cells.
A second type of cell found in
the epidermis is melanocytes.
Melanocytes produces melanin which is the substance
that allows us to block UV rays from the sun.
A third type of cell found in our epidermis
are the Langerhan cells or the immune cells
which are actually macrophages that help us to block
bacteria that are trying to get inside of the body.
And finally, we have the tactile epithelial
cells also referred to as Merkel cells
These are going to help us with
feeling or cutaneous sensations.
There are two different types
of skin found in the integument.
The first type of skin is thin skin.
This is what covers the majority of our
body and excludes the skin of our palms
as well as the palmar surface
of our digits and our toes.
The second type of skin which is going to
cover the palms, digital surfaces of our digits
and the the palms of our feet
is going to be the thick skin.
This skin is hairless.
The epidermis is
composed of multiple layers.
The thin skin contains four layers
whereas the thick skin contains five layers.
Starting from the deepest layer of the
epidermis we have the stratum basale.
The stratum basale is made
up of stem cells and in this layer,
we are going to be as close
to the dermis as possible.
The reason why is because
epithelial tissue is avascular
meaning they do not have
a source of nourishment,
but the stratum basale
is close to the dermis
therefore it is nourished by
the blood vessels in the dermis
Also in this layer, is where
we will find our melanocytes.
Just above or superficial to the
stratum basale is the stratum spinosum.
The stratum spinosum is 8 to 10 layers
of epithelial cells -keratinocytes specifically
that are alive and well also being
nourished from the dermal layer.
Just superficial to the stratum
spinosum is the stratum granulosum.
This is a layer of about
3 to 5 keratinocytes.
The difference in this layer however,
is now we are starting to transition
from living cells in the
epidermis to non-living cells.
The reason why is we are starting to be too
far away from the nourishment of the dermis
and so these cells do not have access
to nutrients and so they are starting to die.
Now located in thick skin only, we
have a layer called the stratum lucidum.
It is actually called the stratum
lucidum because this layer appears clear
when you look at these
cells under the microscope
Now the keratinocytes
are starting to be flattened,
they do not look as squamous as they used to and
they're starting to look a little bit more flat.
There is about 4 to 6 layers of this strata.
And then finally, we
have the stratum corneum.
The stratum corneum is made up
of up to 50 layers of keratinocytes
that are dead and pretty much flattened.
They have very little
cytosol inside of these cells.
It is this layer that is constantly
sloughing off as you go throughout life.
As the skin grows, it grows
from that stratum basale layer
where you have the stem cells
up toward the stratum corneum.
So it's okay that these cells
are breaking off or sloughing off
because they are being
replaced by the layers below.