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The Skin Anatomy, Physiology and Microbiology

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Facebook condo suit again in this video

we're going to look at the skin it

structures and some of the microbes that

live on and within the skin so the skin

is the largest organ in our body here

I'm just drawing a section of the skin

so this can be a section from our arm or

forearm for example the skin is broadly

divided into two layers these are the

epidermis and the dermis there is a

third layer but it's not part of it's

not classified under the skin layers and

this is the subcutaneous layer also

known as the hypodermis the hypodermis

contains subcutaneous tissue

subcutaneous tissue is essentially fat

subcutaneous tissue provides for most of

the body's fat storage and participates

in thermal regulation so when we're cold

it helps us heat up and of course we

have blood vessels veins and arteries

that supply our skin here is a hair

follicle which is essentially our hair

and connecting to the hair follicle it

are the sebaceous glands sebaceous

glands are found all over the body

except the palm and soul of our feet it

secretes sebum sebum will lubricate our

hair and sort of waterproofs our skin

and it also is sebum is also effective

as a defense mechanism against the

pathogens within the sebaceous glands

and reciting around the hair follicle we

actually have some commensal pathogens

pathogens of the hair follicle and

sebaceous glands are these rod-shaped

bacteria known as Propionibacterium

which is a gram positive now what's

interesting about the sebaceous glands

is that it's stimulated actually by the

presence of some hormones such as

androgens and testosterone

these will stimulate the sebaceous

glands to produce more sebum and also

causes I guess hypertrophy hypertrophy

of the sebaceous glands connecting to

the hair follicle we have what's known

as the erector pili muscle this muscle

essentially pulls the hair and the

phenomenon known as the goosebumps is

due to this erector pili muscle

contracting which will pull which will

pull our hair follicle causing our hel

hairs to stick up straight now we talked

about the sebaceous gland but another

important gland in our skin is known as

the sweat gland and as you may have

guessed it secretes sweat but there are

two types of sweat glands these are the

eccrine sweat glands and the apocrine

sweat glands the eccrine sweat glands

are found in palms of our hands and

soles of our feet they're also found on

the forehead the epic rhyme sweat glands

are mainly found in the axillary and

anal genital area they're actually

become functional after we have our

puberty stage and of course within the

skin we found nerves and we find several

types of nerves which I won't go into

but that's just important to know so now

that we know a bit of the structures

within the skin let's look at some of

the functions the overall functions the

skin do does so the skin as I mentioned

is a largest organ in our body the skin

provides protection from the environment

such as if for from abrasion or from

fluid loss the skin is also like a

containment for the body structures and

vital organs the skin is important heat

regulation and this is a sweating

dilation and constriction of blood

vessels the skin is important for

sensation as we have nerve endings on

our skin we can feel things and this is

quite important the skin is also

responsible for part of the synthesis

and for the storage of vitamin d

the skin is also blood reservoir and

it's important in the excretion of

unwanted substances through sweat so

those are the main functions of the skin

so going back to our anatomy of the skin

here the structure as I mentioned the

skin can be broadly divided into two

layers the epidermis and the dermis

now the dermis is just made up of

connective tissue essentially the

epidermis is made up of epithelial cells

but that epidermis can actually be

divided into different layers as well so

let's take a closer look so here we're

assuming into the epidermis layer we

have here the basement membrane that

essentially connects the epithelial

layer on top to the connective tissue

layer down the bottom the very first

layer of the epidermis closest to the

dermis is known as a stratum bacilli the

stratum basale is where we have

epithelial cells that are dividing and

some of these new cells will move up and

these cells are able to divide because

they're receiving blood supply from the

dermis and therefore they are able to

divide and so these cells as they divide

some of them will migrate upwards to the

top of the epidermis the second layer on

top of the stretcher

Vasily is the stratum spinosum the

stratum spinosum are where the cells are

where the epithelial cells are becoming

keratinized because they're not

receiving any blood vessels any blood

supply there are also other cells found

in this area such as melanocytes

melanocytes produce what's called

produce a substance known as mallanna

and Malayan is responsible for skin

color so the dark the darkening of our

skin is thanks to melanin another cell

that is found in the stratum spinosum

layer is the dendritic cells

the dendritic cells our immune cells

that are responsible for capturing

foreign pathogens or materials and so

it's responsible for protecting our body

above the stratum spinosum we have the

third layer the stratum granulosum the

stratum granulosum are where the cells

as they are migrating up are beginning

to die and they're beginning to flatten

and the organelles within the cells are

essentially being destroyed as I hope

I've depicted in this image and so as

the cells keep migrating up we have the

fourth layer the stratum lucidum which

is essentially the cells are dead and

becoming more flattened the very top

layer of the epidermis is known as a

stratum corneum and these are where the

old cells are being shed off and they're

really flat and super thin and so as you

for example you're rubbing your arm

you're actually shedding off your

stratum corneum so some textbooks

actually say that there that the

epidermis can be divided into four

layers others five but here I have

represented the epidermis as five layers

so from the bottom it's the stratum

basale

then it's the stratum spinosum stratum

granulosum stratum lucidum and stratum

corneum and as I mentioned it's the

stratum basale that is that is dividing

and essentially these these new cells

that are dividing or pushing the other

cells up hope that makes sense now that

we have a better understanding of the

skin it's anatomy and the cells that

make up the skin let's look at some of

the microorganisms that live on our skin

because we actually have many millions

of microorganisms that live on our skin

and they live there in unison with us

without causing any infections

of course however if we do have a cut or

something that occurs these

microorganisms can then cause an

infection

so commensal microorganisms are

organisms that live in unison with with

with its with its host some well known

microorganisms that live on on humans

are Staphylococcus species and these are

gram positive gram positive caucuses

round shaped bacteria then we have a

corneal bacterium species and these are

gram positive and they're rod-shaped

bacteria we also have Maya bacterium

species which are acid-fast

bacteria so these are some of the

commensal microorganisms that live in

our skin now let's look at some common

skin infections now with skin infections

the the main cause of skin infections

are actually our commensal

microorganisms the organisms that

usually live on our skin why is this

well our skin can be cut can we can have

burns to our skin we can fold down and

scrape our skin and this will

essentially create a situation or ideal

environment for these microorganisms to

cause an infection so common skin

infections are for example caused by

Staphylococcus aureus which can cause

skin infections such as folliculitis

abscesses and PT go and stuff like Arcos

shock syndrome and then we can have

actually corneal bacterium species cause

skin infections such as a wraith rasma

and pitted Kirito lysis streptococcus

species particularly streptococcus

pyogenes which is a group a

streptococcus the only group a

streptococcus can cause skin infections

such as cellulitis aerith's Aerith

erysipelas

amputee go scarlet fever and necrotizing

fish

I know I'm probably not pronouncing some

of these rights so bear with me so these

are some common skin infections caused

by bacteria but there's also infections

caused by viruses and and fungus as well

so some common ones the human papilloma

virus which is abbreviated HPV can cause

warts what we know is what and then we

have the herpes simplex virus which is

HSV which can cause herpes

some fungal infections we have track of

ton which can cause what's known as

tinea and this is quite common in nails

and our feets and yeah and then we also

have Candida albicans which can cause

candy candy eat candy the aces and

Canada albicans is actually a serious

problem in patients that are

immunocompromised and you usually see

many HIV patients or all or or the

elderly suffer from thrush and thrush is

caused by Candida albicans so I hope you

enjoyed this section on the skin and

some of the microbes with of the skin

there's actually next video that we'll

continue on from this which will focus

on abscesses caused by Staphylococcus

aureus or YZ so if you're interested in

abscess and the pathophysiology of

abscesses please watch the next video

thank you