This one guy right here you can see, see how he is kind of gray. It’s a little hard to get
him in focus, but he’s a little bit gray and not quite as pink. And he has a little vacuole around
the outside. That little white space, that’s an artifact of tissue processing when we soak the,
you know, tissue doesn’t come out of your body pink and purple like this. We actually have to
soak it in formaldehyde or formalin, run it through a series of different chemicals to
make sure the tissue doesn't break down, but anyways back to this little cell here. This
little grey cell has this vacuole around the outside and that’s an artifact and the reason
he has that vacuole is because the cell shrinks during processing and its cytoplasm clumps up
to the nucleus and the vacuole forms around the outside because it doesn't have any desmosomes
to hang on to its neighbors. So, that’s a melanocyte. Melanocytes are not hooked up to
their neighbors. In contrast, look at these nuclei over here these are keratinocyte nuclei and they
actually have that little halo, a little vacuole around their nucleus. Their nucleus is kind of
naked floating in the middle of that little space. That’s because when they shrink up, all of their
cytoplasm is hooked up to the desmosomes at the outside of the cell. And it can’t go anywhere,
it’s attached to all of the neighbors, so the poor little nucleus shrinks up and is naked and alone.
So when you see vacuoles in the epidermis and you are trying to decide if it's a keratinocyte or a
melanocyte, if they have the little halo right around the nucleus, it’s probably a
keratinocyte. If the nucleus has a little blob of spidery cytoplasm around it, like that guy,
it’s probably a melanocyte. So these two guys here are melanocytes. And normal melanocytes live along
the basal layer. Here's another one there. You can kind of tell because you would think melanocytes,
their job is what? It's to make melanin pigment that makes your skin turn colors. When you,
when you tan, your skin gets darker. People that have brown or black skin, darker skin patients,
they have more melanin production not more melanocytes, but their melanocytes are just
more active and make more melanin pigment. But you'd say well why are the melanocytes gray and
not brown? That's because the melanocyte has an unusual job. It makes melanin pigment and then
instead of keeping it and hoarding it all to itself, it actually shares it with all of the
the keratinocytes around it. So it has these little finger-like processes called dendrites
and it sends these little dendrites out to the keratinocytes that live directly adjacent to it
and the keratinocytes actually kind of eat the little fingers off of those little dendritic
branches and that’s how they ingest the pigment into their cytoplasm. So you can actually see this
here. It's a little easier in some some places. Here we go. If you look at these cells right here,
let's see if we can go maybe one higher, one higher power, a little closer view. So
this is 600 times magnification. So we don't usually use this in real practice but for a
video this will help. What you can see is that these cells. Oh, hold on, I’ve lost my arrow,
there it is. If you can see these cells right here, see how they have a brown pigment in the
cytoplasm? That pigment is kind of over top of the nucleus. You can see it up here too,
that's kind of like a little umbrella or a cap. And if you look, if you go up this way,
that's where the outside world is, that's where the sun is. So the sun would come down and would
normally hit these little keratinocyte nuclei and, you know, sunlight contains ultraviolet rays and
ultraviolet rays damage DNA and the DNA of cells lives inside the nucleus. And if you damage that
DNA, you can get skin cancer and things like that. So the job of melanin is to kind of try to protect
your skin to absorb some of that light and protect your skin from the damaging rays of the Sun. So I
like to think of it as the melanocyte makes the pigment, see here's another melanocyte. You know
I know? Look it's got a vacuole on the outside and then a little blob of gray cytoplasm stuck
to the nucleus, okay? So he feeds the melanin to all these keratinocytes around him. I don't know
that the cells are actually all boys but I just like to talk to them like they, like that, like
the cells are people, and if you're a pathologist too long, that's what will happen to you too,
so I'm just kidding. Okay anyway the the pigment up there that little, it's like a little hat or
a little umbrella I think to protect the nucleus of the keratinocyte from the Sun. So when you see
a brown pigment, in a cell in the epidermis, it's actually probably a keratinocyte not a melanocyte.
You would, you would think that it should be a melanocyte. So you know with a little practice you
can do this. That little gray guy there that's a melanocyte. All these guys up here that are brown,
those are keratinocytes. So that clip you just watched is an excerpt from my normal skin
histology video and you can watch the whole thing, the links in the description down below. But let's
see if we can practice now and if you learned from that, how to tell these things apart. So
here we see vacuolated cells in the mid level of the spinous layer. Are these keratinocytes
or are they melanocytes? These are keratinocytes, you can see the nuclei are naked and sitting in
the middle of the vacuole and you can see around the outside of the cell there's a little pink
cytoplasm full of keratin filaments and there the little spinous, the little spines, the desmosomes,
that are hooking on the cell to its neighbor. Let's see if we can get higher power to see
that for sure. See a really great example, that's perfect. Naked nucleus, cytoplasm on the outside,
little spines, little desmosomes hooking up the keratin filament and then hooking onto
the next cell. All of these clear vacuolated cells you're seeing here are all artifactual
vacuolation around keratinocytes. So it's a really useful way in here from another area on the same
biopsy again all of those are keratinocytes. Now let me switch to a different case. So this is an
example of an acral lentiginous melanoma. Acral melanomas often have dramatic pagetoid spread. And
look at all of these big ugly cells, obviously the last case I just showed you the cells were
just normal keratinocytes, not atypical cells like here. But these are atypical really nasty
looking melanocytes and they're scattering up, all of these cells that you're seeing here are
scattering up in this what we call pagetoid spread. You can watch my video on melanoma,
the basics of melanoma. I'll put the link to that down below too. But look at these cells,
they do have vacuoles around them. If I can get it in focus, here. They have vacuoles around them but
the space is around the outside and you can see that there's some kind of pinkish or grayish or
sometimes dusty brown cytoplasm sticking to the nucleus so you can see that the space is around
the outside. The artifactual vacuole is around the outside and the cytoplasm is retained clinging to
the nucleus right there. So those are examples and here's another one up here. See this space
around the outside, the cytoplasm is hugging the nucleus and here are more examples here and
then sometimes it gets kind of spidery, like that it's kind of wispy. And let's go to higher power,
wispy and spidery so it's kind of stretching little arms out to the outside but it's still
sticking to the nucleus. So all of these cells here that you see that have spaces around them,
those are all melanocytes. They’re melanoma cells in this case, so that's a useful way to tell apart
melanocytes from keratinocytes. And remember that Langerhans cells can also do this to some extent.
They can have a vacuole space around them and have a little bit of clingy cytoplasm as well.
So telling melanocytes from Langerhans cells can be a little bit more challenging sometimes,
but the point is to be able to tell apart the vacuole artifact of keratinocyte from that seen
in melanocytes. And with some practice and you can do this on your own slides and practice.
It's actually quite easy most of the time. Thanks for watching. Please like the video if you enjoyed
it and subscribe to my channel. Leave any comments or questions in the comment section below. Thanks!