Okay so let's talk about the different divisions or layers of the epidermis and it's very dependent
on where in the body you are the majority of the epidermis is going to be four layers whereas in
the thick skin you're gonna have five layers we're gonna discuss all five layers then we'll
come back to the thin skin okay so we have a few nice visuals here to have an understanding
of where these are located and as well as whether these cells within these layers are alive or dead
and before we go any further I want to discuss apoptosis or cellular death when you're talking
about the epidermis that is a normal typical thing that happens you lose skin cells from
the most superficial layers then you grow new skin cells that will move up and eventually be
sloughed off so very natural it can speed up and be atypical and we'll talk about some of those
disorders at the end of this module so when you're talking about thick skin thick skin is going to be
located in two main areas of your body on your palms and your digits and then on the soles of
your feet as well as the digits associated with that portion of your foot and when you're talking
about the five layers of thick skin we're gonna start from the deepest layer your basale we're
gonna move up to spinosum granulosum-- lucidum and corneum.
Lucidum is only present in thick skin okay so only in thick skin will you had the lucidum layer the layers and the the deepest
are going to be round and alive and capable of reproducing and creating more cells and then the
layers and the more superficial portions are all going to be flat and dead so pretty much
from granulosum up now this is a time that you want to start thinking about mnemonics mnemonics
are huge particularly in anatomy there is a lot of memorization in anatomy so whatever works for
you I'll put up a few options in different areas when I'm discussing particularly when I talk about
musculoskeletal Anatomy but now it's the time to start coming up with your own mnemonics to help
you memorize certain things okay so here we are in terms of the same visual that we've been looking
at in previous modules this is going to be the deepest part of the epidermis your stratum basale
and then we're going to move more superficially to the stratum corneum right underneath here is your
dermis so the deepest part of the skin layer all right so the deepest layer is the stratum
basale this is unique in the fact that it is a single layer of skin so we only have one layer
of cells here this is unique we're not going to have this in any of the other divisions and also
you have different types of cells the majority of the other layers are going to be composed
of almost exclusively keratinocytes but in the stratum basale you can have melanocytes you can
have those Merkel cells that are meeting up with these receptor these neurons and then you can
have Langerhans cells associated with basale as well now this area is going to create new cells so
you're going to have stem cells associated with basale so the continual creation of new cells
which will eventually move more superficially okay now moving a little more superficially from the
stratum basale you're going to have the stratum spinosum and this is going to be numerous layers
of keratinocytes almost exclusively you can have your melanocytes processes moving into this area
as well as those macrophage Langerhans cells but the majority are going to be those kertatinocytes
that are still able to divide and have the creation of new keratinocytes now this name
seems kind of confusing and it's all because of histology so when they were creating slides these
cells would kind of dry up and appear spiny but when you're actually thinking about a living individual
these cells are actually quite robust and quite large in comparison to these other layers now the
intermediate layer when you're talking about the thick skin is the stratum granulosum and
this is a very important area because this is the transition layer some of the cells in this layer
are alive whereas some of the cells are undergoing apoptosis or programmed cell death so you can have
alive and dead cells in the granulosum now in thick skin only you have the stratum lucidum and this is
a fairly nondescript layer it usually is three to five layers of cells thick and it's just composed
of dead keratinocytes so you'll only have these in the thick skin so the palms of your hand and
the soles of your feet and lastly in the most superficial layer so what you can actually see
on other individuals and yourself is the stratum corneum now depending on what area of the body
you're in this is variably thick but these are all going to be dead flattened or squamous cretinous
sites and actually until this layer here these keratinocytes have a unique name corneocytes
so this is the thicker the flat keratinocytes in this region so depending on the area of the body
this can be between five layers to up to 50 cell layers thick so if you think of the palms of your
hand you're gonna have a much more substantial stratum corneum now it usually takes about four
weeks from keratinocytes to be developed in the stratum basale and move superficially to
the stratum corneum but certain things can speed that up abrasions cuts burns can speed up that
process and then in certain disorders similar to psoriasis so this is a chronic skin disorder where
keratinocytes divide and are produced more quickly and move up superficially faster than in a
typical individual and what will happen is you're going to have the creation of what's referred to
as plaque so it'll appear almost white scaly like and then you can have some redness or inflammation
associated with those skin cells as well so what happens is that these cells don't go through the
proper developmental process it goes a little too fast and you do not have the typical corneocyte that you would have in most individuals in the stratum basale or stratum corneum excuse me
now dandruff is actually very similar to this but it's located solely within the scalp so that is a
quick overview in terms of the epidermal layers now we're going to move into the deeper dermis
this actually is only composed of two layers so that one will go a little bit fast but when we
think about the dermis it's actually quite a bit more complex than what we have in the epidermis