Where is the dermis located
The Integumentary System | The Dermis & Hypodermis
welcome back to anatomy and physiology
on catalyst University my name is Kevin
toh cough please make sure to like this
video and subscribe to my channel for
future videos and notifications in this
video we're going to continue our topic
of the Integra mentor II system and
we're gonna look at the layers that are
deep to the epidermis since we covered
the epidermis in the previous video and
those layers are the dermis and the
subcutaneous layer also called the
hypodermis which is not technically part
of the integumentary system so we'll
spend most of our time talking about the
dermis and we're going to default to
this picture here several times so the
dermis is going to be the layer directly
deep to the epidermis remember that the
deepest layer of the epidermis was the
stratum basale and if you look at the
basal side of the stratum basale it's
gonna have a basement membrane and deep
to that we have the dermis and so the
basement membrane is going to be a
structure that anchors the cells of the
stratum basale to the dermis okay
now there are several important
differences between the epidermis and
the dermis one is that the epidermis is
a vascular whereas the dermis is
vascular in fact if you actually were to
take on some kind of sharp object and
cut yourself if you did not bleed then
you did not cut into the dermis you only
penetrated the epidermis since the
epidermis has no blood vessels that's a
vascular you cannot bleed by just simply
piercing the epidermis however if you
take that sharp object and you cut
yourself and you do bleed then you at
the very least penetrated into the
dermis because the dermis has blood
vessels and as we'll see the dermis also
has a lot of sensory receptors it has
hair follicles and it has lots of glands
all right now the dermis overall is
anywhere between half a millimeter to
three millimeters in thickness and it's
composed of two layers one is the
papillary layer let's actually blow this
out the
capillary layer is a thinner part it's
the superficial of the two layers of the
dermis and then the much thicker part
which is the deeper one is the reticular
layer we'll go into more details on
those in a few minutes
both of these are composed of what are
called connective tissue proper I will
go into the specific kinds of that and
within the dermis you have collagen
elastin and reticulum or collagen fibers
elastic fibers and reticular fibers
throughout the entire dermis
there are also motile dendritic cells
recall that dendritic cells are immune
cells that can act as phagocytes to
destroy foreign invaders foreign
materials and basically protect the
integrant airy system and also prevent
those pathogens from penetrating even
deeper so the dermis has dendritic cells
that are mobile motile and then as I
mentioned the dermis is going to be rich
with blood vessels sweat glands
sebaceous glands hair follicles nail
roots if we're in an area that has
fingernails or toenails sensory nerve
endings and muscles called erector pi
line which are muscles that actually
cause the hair to stand on end which is
what happens when you get goose bumps so
let's zoom in on this to take a little
better look here so this structure right
here this is actually a hair follicle
okay this is our hair follicle and we
see the hair sticking out from that now
obviously if the hair has to go out and
we can see it it's gonna have to
penetrate through the epidermis but
overall the hair follicle itself has its
root in the dermis okay so that's where
we find the hair follicle also this
muscle that we see right here so there's
one right here and then there's a muscle
right here this is an erector pile eye
muscle when the erector pile eye muscle
contracts it causes the hair to stand on
end so not only does this happen when
you get goose bumps but if you actually
startle a cat and you see the cat's hair
stand on end that's what's happening
contraction of those erector pili
muscles okay also if we look at these
coiled tubes here's a good example of
one
this is called a merocrine sweat gland
and one type of American sweat gland is
a regular sweat gland like when
you sweat when you go out in hot weather
or you start exercising and the sweat
deposits on the surface of your skin if
you look at these glands they start out
in the dermis as a network of coiled
tubes and then it kind of slithers out
here through the dermis through the
epidermis and onto the surface of the
skin these glands that do this are
called American sweat glands they have a
duct as you see right here and then they
have a pore that penetrates the surface
of the skin as I mentioned merocrine
sweat glands produced the regular sweat
that we normally think of we'll talk
about those in more detail in a separate
video we also have a special kind of
gland called an oil gland or more
specifically sebaceous gland sebaceous
glands are a little bit different and
they're associated with the hair
follicles and what they do is they
deposit their secretions directly onto
the hair itself okay these sebaceous
glands do not produce sweat instead as
you can see here they produce oil and so
if you have an individual who has very
oily skin that means there's more
activity of the sebaceous glands and we
can also see those sebaceous glands like
the American glands in the dermis okay
and obviously what we can see here is
there's plenty of vasculature
represented by these red and blue blood
vessels and then also plenty of sensory
nerve endings okay so all of those
things are plentiful in the dermis as
you can see none of those are in the
epidermis right except for some tactile
cells in the stratum basale as we saw
earlier and then the other thing I
wanted to mention specifically about the
dermis is it's composed of two layers
one was the papillary layer it was
thinner and it's superficial and then
the reticular layer which was deeper and
thicker all right now I won't spend much
time on the reticular layer but I'm just
going to mention one major thing about
it the reticular layer is composed of
dense irregular connective tissue dense
irregular when you have dense irregular
connective tissue the collagen fibers
are arranged in all sorts of directions
not just one direction if the collagen
fibers were arranged in wonder at
and that would be dense regular
connective tissue which we find in
tendons and ligaments
however in dense irregular connective
tissue the fact that the collagen fibers
are arranged in all directions allows
that tissue to resist tension and
torsion in all sorts of directions not
just one direction and so since skin can
be moved in all directions it requires a
much tougher kind of tissue than dense
regular and so the reticular layer is
made of dense irregular now for the
papillary layer the papillary layer is
composed of areolar connective tissue
okay so Arial or loose connective tissue
as it's called and it's named for the
projections it has which are called
dermal papillae okay so these dermal
papillae you see here they kind of cause
this to go up and down and up and down
almost like finger like projections okay
you could even see that in this
micrograph image of the epidermis here's
one dermal papillae right here here's a
second one so these dermal pathway are
like finger of projections that stick
upwards into the epidermis okay and they
project through the epidermis and they
produce epidermal ridges which are
inconsistencies in the structure of the
epidermis they're most pronounced in
thick skin and these epidermal ridges
are also called
fingerprints and the unique arrangement
of these dermal papillae which produce
unique epidermal ridges gives each
person their unique fingerprint but
those dermal papillae are part of the
papillary layer which gives it its name
okay so that's pretty much the major
things there are two the dermis now the
hypodermis which is what it's usually
called for short or the subcutaneous
layer this is not actually part of the
integumentary system but it's sometimes
associated with it because it lies deep
to the dermis now the subcutaneous layer
is composed of two types of tissue one
is areolar or loose connective tissue
and the others adipose connective tissue
or fat
now the adipose tissue is called
subcutaneous fat and overall what the
subcutaneous layers function is is to
pad and
the body okay the fat in it is mainly
what provides the protection but that
fat also does two other things and acts
as an energy reservoir because fat holds
triglycerides which can be liberated for
energy and then also acts as a thermal
insulator to help prevent heat loss in
the course of mammalian development it's
deemed important to hold on to heat as
much as possible and so that fat tissue
that's in the subcutaneous layer helps
with that thermal insulation okay if you
need to dissipate some of that heat and
get rid of it you can always vasodilator
blood vessels in the dermis and that
will get rid of heat but it's more
important to hold on to the heat
actually and that's what the fat and the
subcutaneous layer does okay so
hopefully that makes sense to you and
you learned a little bit of something
about the functions of the dermis and
the hypodermis please make sure to LIKE
this video and subscribe to my channel
for future videos and notifications in
the next video we're gonna discuss some
of the different types of exocrine
glands in the integumentary system and
we did mention a few of these join us
then
