Skin Flashcards
what is skin?
major component of the integumentary system
largest organ
forms principle interface between exetnal envrionment and internal organs
what are the three main layers of the skin?
epidermis
dermis
hypodermis
what are the main functions of skin in terms of protection
protection of internal organs from the environment
water loss
heat loss/temp regulation
microorganism protection
what other main functions does the skin have other that protection
sensation
blood reservoir
metabolic synthesis
immune system
what is the epidermis
upper most layer
stratified
what cells is the epidemris mainly made of
dead cels composed of keratin
what happens to cells in the epidermis?
replaced and are at differing stages of maturation at each layer
differentiate at the bottom and slowly move to the top gathering keratin and die at the top
4 cells in epidermis
keratin bases cell keratinocytes
pigement melanocytes
langerhans cells
merkle cells
what is a keratinocte
major part of epidermis
sent up from basal layer and differentiate
how does kerinatisation occur?
cells at the base are round
they move up and gradually get kerinatised
flattern out and die
more keratin means more protection
where is there more kertain in skin?
feed and places of high abrasion
function of a melanocyte
pigment
how do melanocyte work?
found in the basal layer and have projections out into keratinocytes to give skin tone
what are the two forms or melanin
EU: dark
PH: light
what is the role of melanin?
protection from UV
scatters it and prevents DNA damage to those cells actively dividing at the base of skin
what gives human skin tone variation?
Eumelanin
darker skins have more eumalanin
does everyone have the same amount of melanocyes?
yes
variation in tone comes fromm amount and type of melanin made not the amount of melanocytes
how do melanocyte give colour to skin?
give granules to keratinoctes
colour dependent on how keratinocytes show this
Light skin: melanin packaged into less dense graules
what are melanocyte granules
enzymes
make melanin active igment
what is are merkle cells?
neuroendorcrine cells found in the basal layer
send signals to the nervous system and can make some hormones
more in fingers and toes
what is the function of a Merkel cells
function unknown but thought to have a sensory function perhaps
what is a Langerhans cell?
dendritic antigen presenting cell which acts as an immune cell
sit in the epidermis looking for bacteria and phagocytose it
where do Langerhans cells come from?
bone marrow as monocytes and travel in the blood to epidermis
name the layers of the epidermis from bottom to top
stratum basale (bottom) stratum spinosum stratum granulosum stratum lucidum stratum corneum ( top)
what is the stratum basale
stem cell layer at the bottom of the epidermis differentiated keratinocytes come from here
what is the stratum spinosum
keratinocytes begin to throw out spindles and differetiate
2-4 cells thick
langerhans found here
what is the stratum granulosum
granular tissues where cells rapidly accumulate keratin
cells begin to flatten and become thin
final layer of living cells
what is the stratum lucidum
transparent layer
only found in thick skins such as palms and feed
transitional layer to dead cells
what is the stratum corneum
top layer
dead keratinocytes
layer is thick
production and shedding rates are matched
features of thick skin?
palms and feed
stratum lucidum layer found here
what is the skin like in terms of microbes?
sterile at birth
then colonisation occurs and bacteria from the environment form a flora
what type of bacteria are found on the skin
gram positive
staphylococcus epidermis is common
no net impact largely though
what is the dermis?
papillary and retiular layers
bulk of skin
made of tough connective collgen
what is the reticular layer?
thicker layer, secondary
strength and resiliance
bundles of collagen found here
gives support
what is the papilary dermis?
thin layer adjacent to apidermis
dermal paillae create ridges
what creates fingerprints?
microscopic structures called dermal papillae
they are ridges and projections into the epidermis
where are hair and sweat glands found?
papillary dermis
where is the major blood supplies for the skin
one in between papillar and reticular, nourished the epidermis
one between dermis and hypodermis
what cells are there within the dermis
collagen
fibroblasts
dendrocytes
immune cell
role of a fibroblast in th dermis?
healing
collagen making
large ER to support the making of collagen
what is a dermal dendrocyte
presents antigens and contibutes to healing
what immune cells are found in the dermis
macrophages
T cells
mast cells
what can the dermis sense using neurones?
touch
pressure
pain
hot/cold
three types of neuron cells within the dermis?
pacinian corpuscles
meissner corpulscles
Ruffini curpulscles
what is a pacinian corpuscle
pressure sensitive recprot
long pressure
slow adaptive
what is a meissner corpuscles
touch receptors
fast adapting
what is a ruffini corpuscle
hot and cold receptor
slow adapting
what other receptors are in the dermis?
thermoreceptors
pain nocicepors
proprioceptors
how d ain nociceptors work
fire when noxious stimuli is detected
eg. excessive heat or cold
excessive mechanical pressure
chemicals
how do proprioceptors work
sit in muscles and joints and tell where the limbs are
sense body position and joint movements
tell the brain where the limbs are without seeing them
what does the hypodermis contain?
adipocytes
fat cells
connective tissue
what cells are in the hypodermis
adipose tissue with fat droplets
macrophages
fibroblasts
basement mebrane
what is a blister
water leaks out and is protruded into the dermis
three component units of hair folicles
folicle going into dermis
sebaceous gland
papillary
three phases of hair growth
anagen
catagen
telogen
what is anagen
growth phase of hair
what happens during anagen
stems cells actively divide, hair is extended out from the folicle base
what makes hairs shorter than others eg hair air
shorter anagen stage
what is catagen
atrophy stage in hair growth
what happens during catagen
hair detaches from stem cell papillary layer
no longer grows, no more cells fed int it
what is telogen
resting phase in hair growth
what happens durin telogen
no new cells
hair fals out
new process happens again in cycle
what causes hair shedding in mamals
hormones trigger atrophy and subsequent resting leading to lots of shedding of hair
why is some hair red
unable to make eumelanin
how des hair have colour?
melanocytes transfer melanosomes to give hair colour
the melanoctes sit in folicles
what are nails
dead keratinsed plates covering fingers and toes tip
prtection and dexterity aid
where does the nail begin
at the groove/root
always growing
animal examples of using ketain
claws
horns
hooves
antlers
what are the three types of sweat glands
eccrine
apocrine
sebaceous
what is an eccrine gland
simple tubular structure in the dermis
sits between hair folicles
secretes watery substances to cool skin down
what is an apopcrine gland
opens into hair folciles restriced to armpits and groin
special type of sweat
hormonal
what is a sebaceous gland
everywere except soles and palms
secrete sebum an oily substances
not active till puberty
prevents water evaporation
what is an epidermal stem cell
involved i everyday regeneration of epidermal layeres
what stem cells are found in hair folicles
multipotetnt stem cells that under normal conditions stuply the cells for renewal of hair folicles
hat is a melanocyte stem ell
melanoctes in the hair folicle die during the catagen stage
stem cell population are therefore needed to renew this
where are stem cell population in skin found?
opposed to be found in the hair bulge
what are bulge cells
pluripotent cells that can regnerate lots f things
a multipotent pool for regeneration of whole parts of the skin
in the short term how does the skin heal wounds
platlets are activated
fibrin cots seals the wound off
macrophages and immune cells invade to defend against microbes and clear up debris
on the long term how are wounds in skin dealt with
fibrobasts invade producing collagen and fibre matrix fr skin to form on and rapir
cell the proliferate creating granuar tissue which is dense
in late stages of long term wound healing what happens
more fibroblasts secrete more matrix proteins
end result is a functional tissue
may not look the same but acts the same
why do scars sometimes appear lighter than before?
deep cuts may damage hair folicles and the melanocyte stem cell pool
so the region grows back lighter than before
what causes sunburn
excessive exposure to UV radiaton
what can excessive UV radiation cause
DNA damage
speicifically thaimine-thiamine dimers
in response to UV radiation what happens
inflammatory mediators are released
causes charactisc redness, swelling and pain
body respnds by activating more melanin to protect the skin
where on the body is the dermis thickest
back
whre in the body is the hypodermis thickest
around organs on the abdomen
