The Integumentary System, Part 1 – Skin Deep: Crash Course A&P #6

The Integumentary System, Part 1 – Skin Deep: Crash Course A&P #6


When you hear about your “organs,” you
probably think of your heart, or your liver, or your lungs. Maybe you picture Captain Nemo
playing the organ aboard the Nautilus. Why do they have an organ on a submarine? That
is – that doesn’t make any sense. But your first associations with that term
probably overlook your biggest organ. I’m talking about your skin. The glorious fleshy shroud that keeps the
world out, and you in. Your skin protects your body against infection
and extreme temperatures, maintains your balance of fluids, and even synthesizes vitamin D
for your own personal use. Its many nerve endings allow you to sense
the outside world, and its sweat glands and blood vessels help you maintain a proper temperature
and communicate a whole range of stuff — from your health to your emotions — through things
like blushing, and flushing, and sweating. It also accounts for about 3 to 5 kilograms
of your body weight, and if you could spread it out, it would measure up to two square
meters, enough to cover your bed — the most disgusting, paper-towel-thin, waterproof,
insulating, stretchy, self-repairing, lifetime-lasting quilt on the planet! It comes in lots of different colors, you
can cover it up, or show it off, or tattoo the periodic table on it if you want. And
of course, without it, you would basically shrivel up and die in no time. Together with your hair, nails, and sweat and oil
glands, your skin forms your integumentary system. And if you’ve ever been burned, or had surgery,
or stepped on a nail, you know how fast complications arise when it gets damaged. But it also heals up quite quickly. LAYERS. Like an everlasting gobstopper, the key to
your integumentary system is layers. And although you can’t tell by looking at
it, your skin actually has three of them, each with particular types of cells that have
their own skin jobs, to borrow a phrase from Blade Runner or BSG… whichever you like! The epidermis is the only layer you can actually
see, assuming that your skin is intact, which is why it’s what you think of, when you think of “skin.”
It’s made of stratified squamous epithelial tissue. But the dermis just below it is where most
of the work that skin does gets done, like sweating, and circulating blood, and feeling
everything everywhere all the time. And at the bottom there’s the subcutis, or hypodermis,
composed mostly of adipose or fatty tissue. Each of these layers owes its properties — and
its ability to do its “skin job” — to its unique combination of cells. The bulk of your epidermis, for example, is
made up of cells called keratinocytes, which are the building blocks of that tough, fibrous
protein keratin that gives structure, durability, and waterproofing to your hair, nails, and
outer skin. These cells are constantly dying and being
replaced — you lose millions of them every day, enough to completely replace your epidermis
every 4 to 6 weeks. That’s why if you want to tell the world
you love your mom or commemorate your favorite famous physiologist with a tattoo you gotta
make sure the ink gets below the epidermis. If there’s a cell in the human body that’s
been responsible for causing the most pride and the most prejudice in human history, it’s
another epidermal cell: the melanocyte, the spider-shaped cell that synthesizes melanin,
the pigment that gives skin its color. I’ll spend more time later talking about
why skin color differs around the world, but one thing to keep in mind is that both the
very palest and the very darkest human skins on the planet have about the same number of
melanocytes. Your particular color isn’t about the number
of these cells that you have, but instead about the breadth of their spidery cellular
extensions, which in turn affect the amount of melanin that they contain. But on a cellular level, we’re all the same. Now, your skin, obviously, is also your first
line of defense when it comes to protecting you from the outside world. So it may not
come as a surprise that you have lots of immune system cells in your epidermis as well. These are your dendritic, or Langerhans cells,
which are kinda star-shaped, and like white blood cells and platelets, they actually originate
in your bone marrow. Once they migrate to the epidermis, their long, skinny tendrils
run around the keratinocytes and spend much of their time ingesting the unwanted invaders
that are trying to sneak around your skin. Finally, rounding out the quartet of epidermal
cells, your tactile, or Merkel cells occur deep down at the boundary between the epidermis
and the dermis, where they combine with nerve endings to create a sensory receptor for touch. What’s a little weird, though, is that all
these cells are all organized differently in the skin that covers your body. In fact, in some
places, you have more layers of epidermis than others. Your thick skin — and yes, that’s what
it’s really called — is the tougher stuff on the palms of your hands and the soles your
feet, and it consists of five epidermal layers. Your thin skin covers everything else, with
just four. To get to know what’s going on with your
thick skin, let’s just imagine you’re walking around barefoot in the yard, when
suddenly you feel a shooting pain. You’ve just stepped on a big ol’ nail,
and it’s penetrated all of the layers of your epidermis.
First it pierced your stratum corneum, which means — pardon my Latin — “horny layer.”
This is the outermost layer and also the roughest, made up of about 20 or 30 sheets of dead keratinocyte
cells. This is the layer that you’re always sloughing off and feeding to dust mites, but while it’s in place
it offers basic protection from environmental threats. From there, the nail drives through your stratum
lucidum, or “clear layer.” This holds two or three rows of clear, flat, dead keratinocytes
that are only found in the thick skin of your palms and foot soles. So, in places where you only
have thin skin, this layer is what’s missing. Things start to get more serious in the “granular
layer” or stratum granulosum, because this contains living keratinocytes that are forming
keratin like crazy. This layer looks kind of grainy because those cells are getting
compressed and flattened as they move up through the epidermal layers, maturing as they go. The deeper you go through the layers of the
epidermis, the younger the cells get. Regeneration happens in the lower layers, and new cells
move up toward the surface, maturing along the way, where they eventually die and slough
off from the surface of your skin. This whole process is due in part to the fact
that the epidermis is epithelial, so it’s avascular. That means that all the oxygen
and nutrients that its cells need have to come from the dermis below it. So, as epidermal
cells mature and get bumped up by younger cells forming below them, they move further
and further from the blood supply, and end up essentially suffocating. When that nail cuts through the fourth layer
— the stratum spinosum, or “spiny layer” — it’s getting closer to the point where
cell regeneration, or mitosis, is active. These cells look prickly when they’re dehydrated
for microscope slide preparation — hence the name — and that’s because they contain
filaments that help them hold to each other. And finally, that dang nail touches down on
your deepest, thinnest epidermal level — the “basal layer” or stratum basale. It’s
just a single layer of columnar cells, but it’s like a cell factory where most of that
new-cell production happens. This stratum is also what connects the epidermis to the
layer of skin below it, the dermis. Feelin’ a little overwhelmed by all the
layers? Just remember: “Come Let’s Get Sun Burned” — it’s a pneumonic. I mean, though, who came up with that, because
if you own some skin you know you don’t want to get sunburned! The ultraviolet radiation in the sun can damage
the epidermis, causing elastic fibers to clump up, leading to that tell-tale leather-face
condition. Plus, getting sunburned temporarily depresses your immune system — because, remember,
you have immune cells in your epidermis too — AND the radiation can actually alter your
skin cells’ DNA, leading to skin cancer. We’re gonna go into your skin’s love-hate
relationship with sunlight more next week, but in the meantime, seriously, wear your
sunscreen. Now, skin damage of any kind can get serious
when it affects the dermis, because it’s not only got loads of those collagen and elastin
fibers, which help make your skin strong and elastic, it’s also full of capillaries and
blood vessels. And it houses the nerve fibers that register
sensations like temperature, pressure, and pain, as well as parts of your hair follicles
and oil and sweat glands with the ducts that lead up to the surface of the skin. So, the dermis is where most of the skin’s
work is done, and it does it in just three layers.
The upper, papillary layer is composed of a thin sheet of areolar connective tissue that’s riddled
with little peg-like projections called dermal papillae. These papillae are pretty neat because in
the thick skin of your hands and feet, these tiny protrusions form unique friction ridges
that press up through the epidermis to help our fingers and feet grip surfaces.
Your fingerprints! Just below that papillary layer is the deeper,
thicker reticular layer that makes up 80 percent of your dermis, made up of dense irregular
connective tissue. All of the dynamic parts contained within the dermis — like the nerve
fibers and capillaries — are distributed between both its layers. So any time you get cut enough to bleed or
feel pain, you know that you’ve broken through the epidermis and lacerated the dermis. Which,
by the way, is the layer that tattoo needles have to reach in order to work: It’s the
only way to make tattoos permanent, but also it means getting tattoos hurts. And bleeds. Finally, something of a footnote to your skin
is its third and most basal layer — the subcutis, or hypodermis. It consists of mostly adipose
connective tissue — basically a seam of fat — and it provides insulation, energy storage,
shock absorption, and helps anchor the skin. In short, your hypodermis is where most of
your body fat hangs out. But there are more skin things to discuss,
so in our next lesson we will tackle big questions, like — does lotion really do anything?
How does deodorant work? And what will make my hair soft and shiny and irresistible? For now, though, you learned all about skin,
the main organ of your integumentary system. We looked at the structure, mechanism, and
function of your three layers of skin — the epidermis, dermis, and hypodermis — and their
various sub-layers. We talked about the roles of melanin and keratin cells, what happens
when you step on a nail, how to ensure you get a good tattoo, and why it pays to wear
sunscreen. Thank you for watching, especially to all
of our Subbable subscribers, who make Crash Course possible for themselves and for the
world. To find out how you can become a supporter, just go to subbable.com. This episode was written by Kathleen Yale,
edited by Blake de Pastino, and our consultant, is Dr. Brandon Jackson. Our director and editor
is Nicholas Jenkins, the script supervisor and sound designer is Michael Aranda, and
the graphics team is Thought Café.

Posts created 34269

100 thoughts on “The Integumentary System, Part 1 – Skin Deep: Crash Course A&P #6

  1. 6:28 funny thing is, my friend and I came up with Come, Let's Get Some Books.. And I think I'll stick with it ๐Ÿ˜…

  2. (((3:15)))
    white countries need diversity because we are all the same so lets mix together all the races into one destroying diversity

  3. Doctor can tell me what thickness has the epidermis in the temporal occipital frontal, that is to say that I found the skull, please, I would appreciate it very much

  4. So, if skin was rubbed repetitively over a period of time, would you end up working your way through all the layers and finally into the dermis, making it bleed? in effect, if you wiped hard enough would you start bleeding?

  5. I quickly realized that I've seen Blade Runner too many times, since I instantly thought of Replicants then he said skinjobs.

  6. I was looking for a mnemonic for the strata layers. Come Lets Get Sun Burned is better than I could have imagined. ๐Ÿ™‚

  7. Who ever disliked was a person who canโ€™t understand and does not like education

  8. interesting points ,if anyone else wants to discover online course anatomy and physiology try Panlarko Anatomy Course Planner (Have a quick look on google cant remember the place now ) ? Ive heard some great things about it and my friend got amazing success with it.

  9. The 350 people that unliked this video are probably professors that can't explain it easily as much as crash course does.

  10. I actually don't understand the humor and the reason for it. I need the information. I really appreciate the science. Thanks.

  11. Is it just me or this guys really talks fast ๐Ÿ˜…๐Ÿ˜… itโ€™s hard to keep up when youโ€™re not a native speaker

  12. My dad stepped on a nail at work and it went into his foot a little. His coworkers put that sole onto a piece of wood with the nail still inside and gave it to him๐Ÿ˜‚๐Ÿ˜‚

  13. Thank for the class.Precious and important things are only mentioned.Kindly slow down the class as it is too fast to understand.

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