skin Flashcards
(110 cards)
1
Q
what is the largest organ in the body
A
skin (15-20% of body mass)
2
Q
what are they key roles of the kin
A
- 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)
3
Q
what are the 3 layers of the skin
A
epidermis, dermis and hypodermis
4
Q
what are the properties of the epidermis
A
- outermost layer
- epithelial
- non vascular
- protective
5
Q
what are the properties of the dermis
A
- fibrous connective tissue
- epithelial gland structures ( sweat and sebaceous glands)
- smooth muscle
- vascular
- sensory
6
Q
what are the properties of the hypodermis
A
- not skin
- protective
- adipose & loose
- connective tissue
7
Q
what is the structure of the epidermis
A
- thick keratinized stratified squamous epithelium
- made up on 5 kayers
- consists of 4 epithelial cell types
8
Q
what are the 5 layers of the epidermis
A
- stratum basale
- stratum spinosum
- stratum granulosum
- stratum lucidum
- stratum corneum
9
Q
what is the stratum basale
A
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
10
Q
what is the stratum spinosum
A
keratin fibres (holds cells in place) and lamellar bodies (contain lipids which keep cells moist) accumulate
11
Q
what is the stratum granulosum
A
keratohyalin and a hard protein envelope form; lamellar bodies release lipids, cells die
12
Q
what is the stratum lucidum
A
dead cells containing dispersed karatohyalins
13
Q
what is the stratum corneum
A
dead cells with a hard protein envelope, the cells contain keratin and are surrounded by lipids (waterproof, keeps moisture inside the body)
14
Q
which cell layers do burn victims lose
A
the stratum lucidum and the stratum corneum
15
Q
what are keratinocytes
A
they produce keratin and are the primary cell of the epidermis
16
Q
where do keratinocytes arise
A
in the stratum basale and are pushed to the surface as continuously mitotic cells reproduce
17
Q
what is the key cell type involved in wound healing and why
A
keratinocytes, as they have stem cell properties
18
Q
how are cells in the epidermis connected
A
via desmosomes
19
Q
how is keratin produced
A
as cells migrate
20
Q
what does filaggrin do to keratin
A
it causes keratin fibres to dimerise (keratinisation)
21
Q
what happens to cells at the surface
A
they are keratin-filled plasma membranes
22
Q
what occurs in the basement membrane and the basal cell layer
A
keratinocytes with stem cell properties express keratin isoforms - key role in wound repair
23
Q
what happens in the spinous layer
A
as cells grow upwards, cells express transglutaminases which cross-link junction complexes
24
Q
what happens in the granular layer
A
profillagrin is expressed - this is cleaved to fillagrin which causes keratin filaments to dimerise and form a matrix. transgluataminases cross link
25
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
26
what is eczema caused by
filaggrin mutations which disrupt keratinisation
27
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)
28
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
29
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
30
what are melanocytes
they produce melanin pigments
31
where are melanocytes located
in the stratum basale
32
what do melanocytes make contact with
living keratinocytes
33
what do melanocytes transfer and to where
melanin to keratinocytes
34
what does melanin to
accumulates to shield cell nucleus from UV
35
what are merkel cells
neuroepithelial cells associated with sensory nerve endings
36
what do merkel cells act as
mechanoreceptors
37
what do merkel cells use as a neurotransmitter
glutamate
38
where do merkel cells accumulate
at ridges in fingerprints and hair endings to form a tactile disc
39
what are merkel cells sensitive to
shear and pressure
40
what are langerhans cells
epidermal dendritic cells
41
where are langerhans cells made
in bone marrow - they migrate to the epidermis
42
what do langerhans cells form part of
the immune system within the skin
43
what do langerhans cells function as
microphage-like antigen presenting cells (activate T-cells)
44
how is melanin produced
it is synthesised by tyrosinase conversion of tyrosine through multiple reactions to o-Quinone and ultimately melanin
45
where does skin colour determintation occur
the reaction occurs in melanocytes
46
what are the 2 outcomes of melanin synthesis
- eumelanin (black)
- pheomelanin (red)
47
when cysteine is added to dopaquinone what happpens
skin colour = pale
48
which 2 enzymes determines very dark skin when both are present
dopachrome tautomerase and tyrosine related protein 1
49
what is the tanning response
your skin created a melanin layer to protect UVA from penetrating to the dermal layer
50
what does UVA have no protection against
free radicals
51
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)
52
what are the characteristics of UVA
- longer wavelength
- penetrates dermis
- causes tanning (melanocyte pigmentation)
53
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
54
what is the melanin reaction driven by
UV induced DNA damage
55
what is the melanin reaction sensitive to
UV light
56
where is melanocortin receptor 1 (MCR1) expressed
in melanocyte cell membrane
57
what is the agonist of MCR1
a-melanocyte stimulatinmg hormone (aMSH)
58
where is a-MSH produced
in the dermis
59
what dies activation of MCR1 induce
the microphthalmia-associated transcription factor (MITF)
60
what does the MCR1 drive the expression of
tyrosinase, DCT and TRP1, so favouring eumelanin (black) synthesis
61
why does skin lightening happen
by loss of function mutations in MCR1
62
what happens within MCR1 loss of functions mutations
pheomelanin > eumelanin = red pigmentation
63
what are other factors which determine skin colour
- carotene
- erythema
- nervous erythema (blushing)
- jaundice
- bruising
64
what is carotene
from diet (oranges/carrots)
is deposited in stratum corneum and fatty tissue of hypodermis as a yellow-orange colour
65
what is erythema
re-direction of blood flow to superficial skin capillaries due to irritation, infection or as part of a response to fever
66
what is nervous erythema (blushing)
catecholamine induced vasodilation which pushes blood to skin surface in well perfused areas of skin (cheeks, chest)
67
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
68
what is bruisinhg
injury to capillaries and hypodermis resulting in deposits of bilirubin in skin which cayses colour of bruise (blue/orange/green)
69
what does the dermis do
provides support
70
where does the dermis get its strength
from 2 layers : papilary and reticular
71
what is the papilary
thin, connective tissue with blood vessels
72
what is the reticular
dense, irregular connective tissue with collagen (strength, hydration) and elastin (stretch recoil)
73
how is the epidermis multifunctional
sensory, vascular, hair follicles and sweat glands
74
what are the cell types within the dermis
- epithelial cells (lining of the glands)
- fibroblasts
- macrophages
- mast cells
- WBC's
- smooth muscle (arrector pili)
75
what are the 3 types of gland secretion
- eccrine (=merocrine)
- apocrine
- holocrine
76
what is eccrine gland secretion
secretion is by exocytosis and usually accompanied by fluid movement, cells do not lose cytoplasm during secretion process
77
what is an example of eccrine gland secretion
fluid secreting cells of the sweat gland
78
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
79
what is an example of apocrine gland secretion
sweat gland, mammary gland
80
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
81
what is an example of holocrine gland secretion
sebaceous gland
82
what are the 5 types of skin gland
- eccrine sweat glands (sudoiferous glands)
- apocrine glands
- sebaceous glands
- ceruminous glands (modified apocrine)
- mammary glands
83
what are eccrine sweat glands
coiled, secretory epithelium lined tubes
84
where are eccrine sweat glands located
distributed over entire body (greatest density on palms and soles of feet)
85
where do eccrine sweat glands open up to
the duct opens to pore on surface
86
what kind of secretion happens in eccrine sweat glands after salt re-absorption in upper reaches of the duct
hypotonic
87
what are eccrine sweat glands regulated by
sympathetic NS
88
how many mls of transdermal water loss occurs per day
600
89
what kind of sweat is produces in CF patients
hypertonic as no salt recovery pathway
90
what are apocrine glands
large glands which secrete oily fluid containing proteins, lipids and steroids
91
what is apocrine glands major function
scent: interaction with skin bacteria (corynebacteria) results in odour
92
where do apocrine gland ducts empty into
the hair follicle where secretions mix with sebaceous oils
93
where are apocrine glands found
in axillary and anogenital areas
94
what are sebaceous glands
small holocrine glands which empty into the hair follicle shaft
95
what do sebaceous glands secrete
an oily substance (sebum) which is composed of triglycerides, wax esters, squalene and free fatty acids
also acid mantle
96
what modifies sebaceous gland secretions
sex hormones (testosterone stimulates and estrogens suppresses)
97
how is sweat distrubutes over the skin surface
sebum emulsifies with eccrine sweat secretions
98
what is acid mantle
a thin, acidic (pH4.5-6.2) barrier to pathogens and viruses
99
what is the ceruminous glands
modified apocrine glands
100
where are ceruminous glands secreted and what do they produce
secreted on to guard hairs of ear canal producing ear wax
101
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
102
what are mammary glands
they produce milk
103
what kind of gland origin is mammary glands
has skin origin as either modified apocrine or sebaceous glands
104
what is hair composed of
keratin secreted from hair follicle stem cells
105
what does hair protect the epidermis from
UV, abrasion, bites
106
what are the 3 stages of hair growth
rest (telogen)
growth (anagen)
and cessation (catagen)
107
what determines hair length
duration of the hair growth cycle; eyebrows - 4 months, scalp - 4 years
108
what are nails composed of
keratin secreted from epidermal cells in the nail root
109
what do nails protect
fingertips and toes from bamage
110
what do nails aid
in precision of movement
