skin Flashcards
what is the largest organ in the body
skin (15-20% of body mass)
what are they key roles of the kin
- protection from external environment
- sensory
- absorption (UV = Vit D synthesis)
- secretion (sweat, electrolytes, sebaceous oil, pheromones)
- body temp regulation (high surface area to body volume)
- blood resevoir
- aesthetics (cultural practices)
what are the 3 layers of the skin
epidermis, dermis and hypodermis
what are the properties of the epidermis
- outermost layer
- epithelial
- non vascular
- protective
what are the properties of the dermis
- fibrous connective tissue
- epithelial gland structures ( sweat and sebaceous glands)
- smooth muscle
- vascular
- sensory
what are the properties of the hypodermis
- not skin
- protective
- adipose & loose
- connective tissue
what is the structure of the epidermis
- thick keratinized stratified squamous epithelium
- made up on 5 kayers
- consists of 4 epithelial cell types
what are the 5 layers of the epidermis
- stratum basale
- stratum spinosum
- stratum granulosum
- stratum lucidum
- stratum corneum
what is the stratum basale
made up of stem cells, the growing layer
cells divide by mitosis and some of the newly formed cells become cells fo the more superficial strata
what is the stratum spinosum
keratin fibres (holds cells in place) and lamellar bodies (contain lipids which keep cells moist) accumulate
what is the stratum granulosum
keratohyalin and a hard protein envelope form; lamellar bodies release lipids, cells die
what is the stratum lucidum
dead cells containing dispersed karatohyalins
what is the stratum corneum
dead cells with a hard protein envelope, the cells contain keratin and are surrounded by lipids (waterproof, keeps moisture inside the body)
which cell layers do burn victims lose
the stratum lucidum and the stratum corneum
what are keratinocytes
they produce keratin and are the primary cell of the epidermis
where do keratinocytes arise
in the stratum basale and are pushed to the surface as continuously mitotic cells reproduce
what is the key cell type involved in wound healing and why
keratinocytes, as they have stem cell properties
how are cells in the epidermis connected
via desmosomes
how is keratin produced
as cells migrate
what does filaggrin do to keratin
it causes keratin fibres to dimerise (keratinisation)
what happens to cells at the surface
they are keratin-filled plasma membranes
what occurs in the basement membrane and the basal cell layer
keratinocytes with stem cell properties express keratin isoforms - key role in wound repair
what happens in the spinous layer
as cells grow upwards, cells express transglutaminases which cross-link junction complexes
what happens in the granular layer
profillagrin is expressed - this is cleaved to fillagrin which causes keratin filaments to dimerise and form a matrix. transgluataminases cross link
what happens within the cornified layer
cells die and the cornified layer forms - fillagrin is hydrolyes to AA’s which form a protective water-proof barrier. keratin forms a hard, protective protein matrix
what is eczema caused by
filaggrin mutations which disrupt keratinisation
what happens within eczema
filaggrin mutations reduct amount of filaggrin within the skin, this causes the keratin fibres to not form a sense, flattened barrier - cracks in the skin barrier enable allergens and pathogens to penetrate the dermis - inflammation occurs causing irritation in the skin and other organs (eg asthma)
what happens within normal filaggrin
within the stratum granulosum, profilaggrin is cleaved to small peptides, the filaggrin binds to keratin fibres causing cell flattening to squamous epithelium. in the stratum corneum, keratin fibres are tightly bound together, filaggrin degrades to hydrophobic AA’s, which maintains skin moisture. the intact skin barrier keeps allergens, pathogens and chemical irritants out of the body
is there a link between filaggrin mutations which cause eczema and the severity of athsma
severe asthmatics with eczema are at greater risk of exposure to allergens absorbed through the skin rather than inhaled through the air, where eczema is present, barrier creams may help to prevent asthma attacks
what are melanocytes
they produce melanin pigments
where are melanocytes located
in the stratum basale
what do melanocytes make contact with
living keratinocytes
what do melanocytes transfer and to where
melanin to keratinocytes
what does melanin to
accumulates to shield cell nucleus from UV
what are merkel cells
neuroepithelial cells associated with sensory nerve endings
what do merkel cells act as
mechanoreceptors
what do merkel cells use as a neurotransmitter
glutamate
where do merkel cells accumulate
at ridges in fingerprints and hair endings to form a tactile disc
what are merkel cells sensitive to
shear and pressure
what are langerhans cells
epidermal dendritic cells
where are langerhans cells made
in bone marrow - they migrate to the epidermis
what do langerhans cells form part of
the immune system within the skin
what do langerhans cells function as
microphage-like antigen presenting cells (activate T-cells)
how is melanin produced
it is synthesised by tyrosinase conversion of tyrosine through multiple reactions to o-Quinone and ultimately melanin
where does skin colour determintation occur
the reaction occurs in melanocytes
what are the 2 outcomes of melanin synthesis
- eumelanin (black)
- pheomelanin (red)
when cysteine is added to dopaquinone what happpens
skin colour = pale
which 2 enzymes determines very dark skin when both are present
dopachrome tautomerase and tyrosine related protein 1
what is the tanning response
your skin created a melanin layer to protect UVA from penetrating to the dermal layer
what does UVA have no protection against
free radicals
what are the characteristics of UVC and UVB
- short wavelengths
- extremely damaging
- causes sunburn (only penetrates epidermis)
- low dose (largely filtered out by atmospheric ozone layer)
what are the characteristics of UVA
- longer wavelength
- penetrates dermis
- causes tanning (melanocyte pigmentation)
what are the steps to tanning
- UVA penetration
- DNA damage in dermis
- epithelial DNA damage response
- a melanocyte stimulating hormone (aMSH) synthesised and released from damaged dermal cells
- diffusion to melanocortin receptor (MC1R), a 7 transmembrane GCPR expressed in melanocytes
- microphthalmia-associatd transcription factor (MITF) increases expression of: tyrosinase (TYR), tyrosinase related protein 1 (TYRP1) and dopachrome tautomerase (DCT)
- eumelanin synthesised in melanocytes
- eumelanin > pheomelanin = black colour
what is the melanin reaction driven by
UV induced DNA damage
what is the melanin reaction sensitive to
UV light
where is melanocortin receptor 1 (MCR1) expressed
in melanocyte cell membrane
what is the agonist of MCR1
a-melanocyte stimulatinmg hormone (aMSH)
where is a-MSH produced
in the dermis
what dies activation of MCR1 induce
the microphthalmia-associated transcription factor (MITF)
what does the MCR1 drive the expression of
tyrosinase, DCT and TRP1, so favouring eumelanin (black) synthesis
why does skin lightening happen
by loss of function mutations in MCR1
what happens within MCR1 loss of functions mutations
pheomelanin > eumelanin = red pigmentation
what are other factors which determine skin colour
- carotene
- erythema
- nervous erythema (blushing)
- jaundice
- bruising
what is carotene
from diet (oranges/carrots)
is deposited in stratum corneum and fatty tissue of hypodermis as a yellow-orange colour
what is erythema
re-direction of blood flow to superficial skin capillaries due to irritation, infection or as part of a response to fever
what is nervous erythema (blushing)
catecholamine induced vasodilation which pushes blood to skin surface in well perfused areas of skin (cheeks, chest)
what is jaundice
a liver disease which release bile pigment which are deposited in the hypodermis and the cornea of the eye giving a yellow colour
what is bruisinhg
injury to capillaries and hypodermis resulting in deposits of bilirubin in skin which cayses colour of bruise (blue/orange/green)
what does the dermis do
provides support
where does the dermis get its strength
from 2 layers : papilary and reticular
what is the papilary
thin, connective tissue with blood vessels
what is the reticular
dense, irregular connective tissue with collagen (strength, hydration) and elastin (stretch recoil)
how is the epidermis multifunctional
sensory, vascular, hair follicles and sweat glands
what are the cell types within the dermis
- epithelial cells (lining of the glands)
- fibroblasts
- macrophages
- mast cells
- WBC’s
- smooth muscle (arrector pili)
what are the 3 types of gland secretion
- eccrine (=merocrine)
- apocrine
- holocrine
what is eccrine gland secretion
secretion is by exocytosis and usually accompanied by fluid movement, cells do not lose cytoplasm during secretion process
what is an example of eccrine gland secretion
fluid secreting cells of the sweat gland
what is apocrine gland secretion
lipid, protein and AA laden secretion, major contrubution to scent, cells lose cytoplasm during the secretion process but cell survives the process and regenerates lost material
what is an example of apocrine gland secretion
sweat gland, mammary gland
what is holocrine gland secretion
lipid and AA laden secretions; often waxy, thicker secretion responsible for pungent smell, entire cell ruptures contents into gland lumen, continual cell growth and replacement
what is an example of holocrine gland secretion
sebaceous gland
what are the 5 types of skin gland
- eccrine sweat glands (sudoiferous glands)
- apocrine glands
- sebaceous glands
- ceruminous glands (modified apocrine)
- mammary glands
what are eccrine sweat glands
coiled, secretory epithelium lined tubes
where are eccrine sweat glands located
distributed over entire body (greatest density on palms and soles of feet)
where do eccrine sweat glands open up to
the duct opens to pore on surface
what kind of secretion happens in eccrine sweat glands after salt re-absorption in upper reaches of the duct
hypotonic
what are eccrine sweat glands regulated by
sympathetic NS
how many mls of transdermal water loss occurs per day
600
what kind of sweat is produces in CF patients
hypertonic as no salt recovery pathway
what are apocrine glands
large glands which secrete oily fluid containing proteins, lipids and steroids
what is apocrine glands major function
scent: interaction with skin bacteria (corynebacteria) results in odour
where do apocrine gland ducts empty into
the hair follicle where secretions mix with sebaceous oils
where are apocrine glands found
in axillary and anogenital areas
what are sebaceous glands
small holocrine glands which empty into the hair follicle shaft
what do sebaceous glands secrete
an oily substance (sebum) which is composed of triglycerides, wax esters, squalene and free fatty acids
also acid mantle
what modifies sebaceous gland secretions
sex hormones (testosterone stimulates and estrogens suppresses)
how is sweat distrubutes over the skin surface
sebum emulsifies with eccrine sweat secretions
what is acid mantle
a thin, acidic (pH4.5-6.2) barrier to pathogens and viruses
what is the ceruminous glands
modified apocrine glands
where are ceruminous glands secreted and what do they produce
secreted on to guard hairs of ear canal producing ear wax
what does ear wax do
keeps eardrum pliable, lubricates and waterproofs the canal, kills bacteria, and traps foreign particles (dust, fungal spores, etc) by coating the guard hairs of the ear
what are mammary glands
they produce milk
what kind of gland origin is mammary glands
has skin origin as either modified apocrine or sebaceous glands
what is hair composed of
keratin secreted from hair follicle stem cells
what does hair protect the epidermis from
UV, abrasion, bites
what are the 3 stages of hair growth
rest (telogen)
growth (anagen)
and cessation (catagen)
what determines hair length
duration of the hair growth cycle; eyebrows - 4 months, scalp - 4 years
what are nails composed of
keratin secreted from epidermal cells in the nail root
what do nails protect
fingertips and toes from bamage
what do nails aid
in precision of movement
