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


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

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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