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Structure Of The Skin - Layers Of Skin - Types Of Skin - Types Of Skin Cells - Integumentary System

in this video we're going to go over the

makeup or structure

of skin human skin which is also called

the integument

or the cutaneous membrane is made up of

two layers

the epidermis and the dermis which are

labeled on this model of skin

the subcutaneous layer at the bottom has

also been labeled

however it is not actually part of the

structure of skin

but it's connected to the dermis of the

skin i will also be drawing in some

components

that are not actually on this model

let's start by looking at the epidermis

the epidermis consists of four to five

layers depending on the type of skin

thick skin has five layers and it is

found in the palms of the hands

and on the soles of the feet thin skin

has four layers and is what covers most

of the body

the skin model we're looking at has all

five layers

the bottom or deep layer is called the

stratum basal

it is made up of a single layer of cells

attached to a basement membrane

there are three types of cells in the

stratum basal keratinocytes

melanocytes and tactile cells

keratinocytes are the most common cell

in this layer

and they go through cell division to

replace cells that are shed from the

surface of the skin

these cells can produce a tough

structural protein called keratin

which strengthens the skin and makes it

almost waterproof

melanocytes are scattered among the

keratinocytes

and they produce the pigment melanin in

reaction to exposure to ultraviolet

light

melanin gets transferred to

keratinocytes and surrounds the nucleus

to protect dna from mutating

from ultraviolet radiation tactile cells

are also scattered among the

keratinocytes

and they serve as light touch receptors

the next layer

moving upwards in the epidermis is the

stratum spinosum

this layer is made up of daughter

keratinocytes made from dividing cells

in the stratum basal layer below

and epidermal dendritic cells the

daughter keratinocytes connect to

neighboring cells desmosomes

which are one of the ways cells connect

to one another giving them a prickly

appearance

the dendritic cells are immune cells

that help fight infections in the skin

moving upwards the next layer is the

stratum granulosum

this layer is comprised of three to five

layers of keratinocytes

the process of keratinization begins in

this layer of the epidermis

keratinization is where the

keratinocytes fill with the keratin

protein mentioned earlier

this process continues as the cells move

upwards in the epidermis

and as it continues the cells nucleus

and organelles are eliminated

and the cell dies the next layer up is

the stratum lucidum

this layer is only found in the thick

skin in the palms and soles of the feet

the keratinocytes in this layer are

clear flat

closely packed and have no nucleus or

organelles

they are also filled with the protein

called illidan which is eventually

transformed

into keratin the last or top layer is

called the stratum corneum

this layer is comprised of dead

keratinized cells

it takes about two weeks for the new

keratinocyte to reach the stratum

corneum

and it remains in this layer for about

another two weeks before it is shed

now let's look at the dermis the dermis

is comprised of connective tissue proper

with collagen being the most plentiful

type of fiber

found throughout the dermis the dermis

also houses other structures

such as blood vessels hair follicles

sweat glands

sebaceous glands which secrete a

lubricating oil

sensory nerve endings nail roots and

erector pili muscles

which affect hair follicles we will

cover these structures

in depth in future videos the dermis has

two layers

a papillary layer and a reticular layer

the papillary layer is the top

superficial layer of the dermis

it is composed of loose connective

tissue and forms bumps

or projections called dermal papillae

that fit with the epidermal ridges

of the epidermis the form of the dermal

papillae

and epidermal ridges increases the

surface area of contact between the two

layers

the dermal papillae contain capillaries

that supply nutrients to the cells of

the epidermis

and they contain sensory nerve endings

that help monitor touch

on the surface of the skin the reticular

layer is composed of dense connective

tissue

with some elastic fibers and many

bundles of collagen fibers

and it extends to the deeper

subcutaneous layer

the subcutaneous layer which again is

not part of the skin

is located below or deep to the dermal

layer of the skin

this layer is often referred to as the

hypodermis

and it consists of loose connective

tissue and adipose connective tissue

or fat tissue many times it is referred

to

as subcutaneous fat this layer helps

bind the skin to underlying structures

acts as a cushion protects the body

provides insulation

and provides for energy storage and that

be the basics on the structure of the

skin