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human epithelial biology > skin > Flashcards

skin Flashcards

1
Q

what is the largest organ in the body

A

skin (15-20% of body mass)

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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)
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3
Q

what are the 3 layers of the skin

A

epidermis, dermis and hypodermis

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4
Q

what are the properties of the epidermis

A
  • outermost layer
  • epithelial
  • non vascular
  • protective
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5
Q

what are the properties of the dermis

A
  • fibrous connective tissue
  • epithelial gland structures ( sweat and sebaceous glands)
  • smooth muscle
  • vascular
  • sensory
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6
Q

what are the properties of the hypodermis

A
  • not skin
  • protective
  • adipose & loose
  • connective tissue
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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
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8
Q

what are the 5 layers of the epidermis

A
  • stratum basale
  • stratum spinosum
  • stratum granulosum
  • stratum lucidum
  • stratum corneum
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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

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10
Q

what is the stratum spinosum

A

keratin fibres (holds cells in place) and lamellar bodies (contain lipids which keep cells moist) accumulate

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11
Q

what is the stratum granulosum

A

keratohyalin and a hard protein envelope form; lamellar bodies release lipids, cells die

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12
Q

what is the stratum lucidum

A

dead cells containing dispersed karatohyalins

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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)

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14
Q

which cell layers do burn victims lose

A

the stratum lucidum and the stratum corneum

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15
Q

what are keratinocytes

A

they produce keratin and are the primary cell of the epidermis

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16
Q

where do keratinocytes arise

A

in the stratum basale and are pushed to the surface as continuously mitotic cells reproduce

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17
Q

what is the key cell type involved in wound healing and why

A

keratinocytes, as they have stem cell properties

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18
Q

how are cells in the epidermis connected

A

via desmosomes

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19
Q

how is keratin produced

A

as cells migrate

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20
Q

what does filaggrin do to keratin

A

it causes keratin fibres to dimerise (keratinisation)

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21
Q

what happens to cells at the surface

A

they are keratin-filled plasma membranes

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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

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23
Q

what happens in the spinous layer

A

as cells grow upwards, cells express transglutaminases which cross-link junction complexes

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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

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25
Q

what happens within the cornified layer

A

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

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26
Q

what is eczema caused by

A

filaggrin mutations which disrupt keratinisation

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27
Q

what happens within eczema

A

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)

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28
Q

what happens within normal filaggrin

A

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

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29
Q

is there a link between filaggrin mutations which cause eczema and the severity of athsma

A

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

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30
Q

what are melanocytes

A

they produce melanin pigments

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31
Q

where are melanocytes located

A

in the stratum basale

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32
Q

what do melanocytes make contact with

A

living keratinocytes

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33
Q

what do melanocytes transfer and to where

A

melanin to keratinocytes

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34
Q

what does melanin to

A

accumulates to shield cell nucleus from UV

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35
Q

what are merkel cells

A

neuroepithelial cells associated with sensory nerve endings

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36
Q

what do merkel cells act as

A

mechanoreceptors

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37
Q

what do merkel cells use as a neurotransmitter

A

glutamate

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38
Q

where do merkel cells accumulate

A

at ridges in fingerprints and hair endings to form a tactile disc

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39
Q

what are merkel cells sensitive to

A

shear and pressure

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40
Q

what are langerhans cells

A

epidermal dendritic cells

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41
Q

where are langerhans cells made

A

in bone marrow - they migrate to the epidermis

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42
Q

what do langerhans cells form part of

A

the immune system within the skin

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43
Q

what do langerhans cells function as

A

microphage-like antigen presenting cells (activate T-cells)

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44
Q

how is melanin produced

A

it is synthesised by tyrosinase conversion of tyrosine through multiple reactions to o-Quinone and ultimately melanin

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45
Q

where does skin colour determintation occur

A

the reaction occurs in melanocytes

46
Q

what are the 2 outcomes of melanin synthesis

A
  • eumelanin (black)
  • pheomelanin (red)
47
Q

when cysteine is added to dopaquinone what happpens

A

skin colour = pale

48
Q

which 2 enzymes determines very dark skin when both are present

A

dopachrome tautomerase and tyrosine related protein 1

49
Q

what is the tanning response

A

your skin created a melanin layer to protect UVA from penetrating to the dermal layer

50
Q

what does UVA have no protection against

A

free radicals

51
Q

what are the characteristics of UVC and UVB

A
  • short wavelengths
  • extremely damaging
  • causes sunburn (only penetrates epidermis)
  • low dose (largely filtered out by atmospheric ozone layer)
52
Q

what are the characteristics of UVA

A
  • longer wavelength
  • penetrates dermis
  • causes tanning (melanocyte pigmentation)
53
Q

what are the steps to tanning

A
  • 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
Q

what is the melanin reaction driven by

A

UV induced DNA damage

55
Q

what is the melanin reaction sensitive to

A

UV light

56
Q

where is melanocortin receptor 1 (MCR1) expressed

A

in melanocyte cell membrane

57
Q

what is the agonist of MCR1

A

a-melanocyte stimulatinmg hormone (aMSH)

58
Q

where is a-MSH produced

A

in the dermis

59
Q

what dies activation of MCR1 induce

A

the microphthalmia-associated transcription factor (MITF)

60
Q

what does the MCR1 drive the expression of

A

tyrosinase, DCT and TRP1, so favouring eumelanin (black) synthesis

61
Q

why does skin lightening happen

A

by loss of function mutations in MCR1

62
Q

what happens within MCR1 loss of functions mutations

A

pheomelanin > eumelanin = red pigmentation

63
Q

what are other factors which determine skin colour

A
  • carotene
  • erythema
  • nervous erythema (blushing)
  • jaundice
  • bruising
64
Q

what is carotene

A

from diet (oranges/carrots)
is deposited in stratum corneum and fatty tissue of hypodermis as a yellow-orange colour

65
Q

what is erythema

A

re-direction of blood flow to superficial skin capillaries due to irritation, infection or as part of a response to fever

66
Q

what is nervous erythema (blushing)

A

catecholamine induced vasodilation which pushes blood to skin surface in well perfused areas of skin (cheeks, chest)

67
Q

what is jaundice

A

a liver disease which release bile pigment which are deposited in the hypodermis and the cornea of the eye giving a yellow colour

68
Q

what is bruisinhg

A

injury to capillaries and hypodermis resulting in deposits of bilirubin in skin which cayses colour of bruise (blue/orange/green)

69
Q

what does the dermis do

A

provides support

70
Q

where does the dermis get its strength

A

from 2 layers : papilary and reticular

71
Q

what is the papilary

A

thin, connective tissue with blood vessels

72
Q

what is the reticular

A

dense, irregular connective tissue with collagen (strength, hydration) and elastin (stretch recoil)

73
Q

how is the epidermis multifunctional

A

sensory, vascular, hair follicles and sweat glands

74
Q

what are the cell types within the dermis

A
  • epithelial cells (lining of the glands)
  • fibroblasts
  • macrophages
  • mast cells
  • WBC’s
  • smooth muscle (arrector pili)
75
Q

what are the 3 types of gland secretion

A
  • eccrine (=merocrine)
  • apocrine
  • holocrine
76
Q

what is eccrine gland secretion

A

secretion is by exocytosis and usually accompanied by fluid movement, cells do not lose cytoplasm during secretion process

77
Q

what is an example of eccrine gland secretion

A

fluid secreting cells of the sweat gland

78
Q

what is apocrine gland secretion

A

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
Q

what is an example of apocrine gland secretion

A

sweat gland, mammary gland

80
Q

what is holocrine gland secretion

A

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
Q

what is an example of holocrine gland secretion

A

sebaceous gland

82
Q

what are the 5 types of skin gland

A
  • eccrine sweat glands (sudoiferous glands)
  • apocrine glands
  • sebaceous glands
  • ceruminous glands (modified apocrine)
  • mammary glands
83
Q

what are eccrine sweat glands

A

coiled, secretory epithelium lined tubes

84
Q

where are eccrine sweat glands located

A

distributed over entire body (greatest density on palms and soles of feet)

85
Q

where do eccrine sweat glands open up to

A

the duct opens to pore on surface

86
Q

what kind of secretion happens in eccrine sweat glands after salt re-absorption in upper reaches of the duct

A

hypotonic

87
Q

what are eccrine sweat glands regulated by

A

sympathetic NS

88
Q

how many mls of transdermal water loss occurs per day

A

600

89
Q

what kind of sweat is produces in CF patients

A

hypertonic as no salt recovery pathway

90
Q

what are apocrine glands

A

large glands which secrete oily fluid containing proteins, lipids and steroids

91
Q

what is apocrine glands major function

A

scent: interaction with skin bacteria (corynebacteria) results in odour

92
Q

where do apocrine gland ducts empty into

A

the hair follicle where secretions mix with sebaceous oils

93
Q

where are apocrine glands found

A

in axillary and anogenital areas

94
Q

what are sebaceous glands

A

small holocrine glands which empty into the hair follicle shaft

95
Q

what do sebaceous glands secrete

A

an oily substance (sebum) which is composed of triglycerides, wax esters, squalene and free fatty acids
also acid mantle

96
Q

what modifies sebaceous gland secretions

A

sex hormones (testosterone stimulates and estrogens suppresses)

97
Q

how is sweat distrubutes over the skin surface

A

sebum emulsifies with eccrine sweat secretions

98
Q

what is acid mantle

A

a thin, acidic (pH4.5-6.2) barrier to pathogens and viruses

99
Q

what is the ceruminous glands

A

modified apocrine glands

100
Q

where are ceruminous glands secreted and what do they produce

A

secreted on to guard hairs of ear canal producing ear wax

101
Q

what does ear wax do

A

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
Q

what are mammary glands

A

they produce milk

103
Q

what kind of gland origin is mammary glands

A

has skin origin as either modified apocrine or sebaceous glands

104
Q

what is hair composed of

A

keratin secreted from hair follicle stem cells

105
Q

what does hair protect the epidermis from

A

UV, abrasion, bites

106
Q

what are the 3 stages of hair growth

A

rest (telogen)
growth (anagen)
and cessation (catagen)

107
Q

what determines hair length

A

duration of the hair growth cycle; eyebrows - 4 months, scalp - 4 years

108
Q

what are nails composed of

A

keratin secreted from epidermal cells in the nail root

109
Q

what do nails protect

A

fingertips and toes from bamage

110
Q

what do nails aid

A

in precision of movement

human epithelial biology (5 decks)

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