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Dermatology > Structure & Function of Skin > Flashcards

Structure & Function of Skin Flashcards

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Dermatology Board Prep flashcards
1
Q

skin layers

A

epidermis

dermis

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2
Q

epidermis

A

outer layer, stratified squamous epithelium (skin proper)

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3
Q

demis

A

beneath epidermis, connective tissue

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4
Q

which granular layer does epidermis come from & how?

A

ectoderm cells form single layer periderm, gradual increase in layers of cells & periderm cells are cast off

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5
Q

which granular layer does dermis come from?

A

formed from mesoderm below ectoderm

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6
Q

where do melanocytes come from and what is their function?

A

pigment producing cells from neural crest

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7
Q

if there is a defect in one stem cell, how will the lesion appear?

A

it will follow Blaschko’s lines & will be asymmetrical

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8
Q

what does the skin consist of?

A

epidermis, appendages, derma-epidermal junction, dermis & sub-cutis

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9
Q

which cells make up the epidermis?

A

mostly keratinocytes
melanocytes
Langerhans cells
Merkel cells

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10
Q

how many layers does the epidermis have?

A 
4 defined layers:
keratin layer
granular layer 
prickle cell layer
basal layer
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11
Q

how do the epidermal stem cells divide?

A

divide at bottom & migrate to the top

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12
Q

palms & soles skin

A

thick coat of keratin over normal layer

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13
Q

abdominal skin

A

very thin epidermis, glands & hair follicles more pronounced

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14
Q

what is epidermal turnover?

A

how fast keratinocytes travel upwards

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15
Q

how is epidermal controlled?

A

growth factors
cell death
hormones

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16
Q

what happens if control of epidermal turnover is lost?

A

skin cancer

psoriasis

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17
Q

how long does migration of keratinocytes usually take?

A

28 days from bottom to top

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18
Q

how long does migration of keratinocytes take in psoriasis?

A

45 days

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19
Q

describe the basal layer

A

usually one small cuboidal cell thick, lots of intermediate filaments (keratin), highly metabolically active

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20
Q

describe the prickle cell layer

A

larger polyhedral cells, lots of desmosomes which intermediate filaments connect to

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21
Q

how does intra-epidermal blistering occur?

A

a build up of hydrostatic pressure which busts apart the relatively delicate cells (desmosomes detach) within the epidermis, more water gets pumped in & a fragile roof is formed on top which will eventually pop with any change of pressure. e.g. baby nappy rash

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22
Q

describe the granular layer?

A

very thin layer of 2-3 flattened cells, large keratohyalin granules contain flaggrin & involcurin proteins, has a high lipid content & Odland bodies. no cell nuclei.

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23
Q

where do cells die?

A

the granular layer where they spit out material which will be used to seal off & prevent water loss
the main component of this material is flaggrin

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24
Q

what is missing from the skin in eczema?

A

flaggrin

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25
Q

describe the keratin layer?

A

final top layer. Has an insoluble cornified envelope. mostly keratin and some filaggrin. lamellar granules release lipids. creates a tight waterproof barrier.

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26
Q

what are corneocytes?

A

overlapping non-nucleated cell remnants

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27
Q

describe the oral mucosa

A

masticatory - keratinised to deal with friction and pressure
lining mucosa - non-keratinised
specialied mucosa (tongue papillae) - taste

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28
Q

describe the ocular mucosa

A

has lacrimal glands & sebaceous glands and eye lashes for specialist functions

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29
Q

white lesions in skin (nail beds & mucosal membranes) is what?

A

thickening of normally thin epidermis so that you can’t see blood vessels anymore

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30
Q

what’s the difference between skin & scar tissue?

A

scar tissue has no appendages (hair follicles/nails)

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31
Q

is the dermis or epidermis thicker?

A

dermis is thicker

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32
Q

what are the majority of epidermal cells?

A

keratinocytes

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33
Q

what are the other epidermal cells?

A

melanocytes
Langerhans cells
merkel cells

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34
Q

which epidermal layer are melanocytes found in?

A

basal & suprabasal

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35
Q

which epidermal layer are Langerhans cells found in?

A

suprabasal

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36
Q

which epidermal layers are Merkel cells found in?

A

basal

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37
Q

when do melanocytes migrate & where during foetal development?

A

in the first 3 months

from the epidermis to neural crest

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38
Q

what are melanocytes?

A

pigment producing dendritic cells

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39
Q

how do melanocytes produce pigment?

A

convert tyrosine to melanin pigment;

  • eumelanin (brown or black)
  • phaeomelanin (red or yellow)
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40
Q

what are melanin organelles/granules called?

A

melanosomes

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41
Q

Full melanocytes are transferred where and how from epidermal cells?

A

to adjacent keratinocytes via dendrites

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42
Q

what do melanocytes form a protective cap over?

A

the nucleus

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43
Q

what cell type are melanocytes?

A

neuronal as they are evolved from the neural crest.

similar properties to astrocytes

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44
Q

what is vitiligo?

A

an autoimmune disease with loss of melanocytes, can be seen in both black/white people but more obvious in black people.

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45
Q

what is albinism?

A

the partial loss of pigment production

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46
Q

what is Nelson’s syndrome?

A

a melanin stimulating hormone is produce in excess by the pituitary causing an overproduction of eumelanin.

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47
Q

where do Langerhans cells originate from?

A

mesenchymal origin - bone marrow

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48
Q

where are langerhans cells found?

A

strategically dispersed in prickle cell level in epidermis. Also found in dermis & lymph nodes.

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49
Q

what do Langerhans cells do?

A

involved in skin immune system;

  • Ag presenting cells
  • pick up Ag in skin & circulate to lymph nodes via lymphatics.
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50
Q

which granules are present in Langerhans cells & why?

A

birbeck granules but we don’t know why

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51
Q

what are Merkel cells for?

A

responsible for sense of touch - mechanoreceptors

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52
Q

where are Merkel cells found?

A

in the basal layer between keritanocytes & nerve fibres

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53
Q

where do Merkel cells synapse?

A

directly with free nerve endings

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54
Q

what part of the free nerve endings does diabetes affect?

A

diabetes affects the myelin sheath which causes reduced/no/funny feeling.

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55
Q

is Merkel cell carcinoma more common the melanomas?

A

no but is more deadly than melanoma.

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56
Q

what is a pilosebaceous unit?

A

a hair follicle;

  • epidermal component + dermal papilla
  • specialised keratins
  • adjacent sebaceous gland
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57
Q

how is hair pigmented?

A

via melanocytes above the dermal papilla of a pilosebaceous unit which melanise the matrix of a hair

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58
Q

name some functions of a pilosebaceous unit

A
  • sensory
  • reduces need for melanocytes
  • is the origin of the gland which supplies moisture to the skin surface
59
Q

where are the stem cells of a pilosebaceous unit?

A

in the dermal root sheath

60
Q

what are the phases of growth of hair?

A

anagen, catagen & telogen

61
Q

what happens during anagen?

A

hair grows

over 1-8 years

62
Q

what happens during catagen?

A

the hair involutes

63
Q

what happens during telogen?

A

shedding phase

64
Q

what can affect the speed of hair growth?

A

hormones but hair will usually go through phases like clockwork

65
Q

how is a hair shed?

A

through dermal papilla dissociation which always takes about 4 weeks

66
Q

what is virilisation?

A

excessive & rapid hair growth

e.g. due to excess androgen from a tumour

67
Q

what is alopecia areata?

A

autoimmune hair loss

normal hair -> grey hair -> hair loss

68
Q

what are nails?

A

specialised keratins

69
Q

which part of a nail is a hair bulb similar to?

A

nail matrix/root

70
Q

where is the nail matrix found?

A

just below the skin surface proximal to the cuticle

71
Q

what can a crumbly nail be due to?

A
  • fungus

- repeated small traumas

72
Q

what is the cannula of a nail?

A

the thick layer which creates a white semi circle at the base of the nail

73
Q

what is the derma-epidermal junction?

A

the interface between epidermis & dermis, complicated structure

74
Q

what does the DEJ have a key role in?

A

epithelial-mesenchymal interactions:

  • support, anchorage, adhesion, growth & differentiation of epidermal cells
  • semi-permeable membrane acts as a filter & barrier
75
Q

where does the epidermis get it’s blood supply?

A

the dermis

also brings nutrients & takes away waste

76
Q

name the two layers of the DEJ

A

lamina densa & lamina lucida

77
Q

where are hemidsemosomes found?

A

in basal cells of epidermis

78
Q

what are hemidesmosomes?

A

filaments that attach to proteins in the lamina lucida

79
Q

what happens in an inherited disease of the DEJ?

A

a mutation in one of the proteins in the DEJ causes skin fragility

80
Q

what happens in an acquired disease of the DEJ?

A

auto-antibodies against proteins in the DEJ are formed

81
Q

describe epidermolysis bullosa simplex

A

caused by inherited defect of DEJ
lots of blistering, very fragile skin, mum can’t hold it properly, tearing of skin, can become severe enough to cause webbing of toes & fingers

82
Q

describe bullous pemphigoid

A

can come on at any point in life (acquired)
defect in skin tethering, not stuck together very well causing blistering & a severe itch
controlled by steroids

83
Q

What are the components of the Dermis?

A
  • cells
  • fibres
  • ground substance
    blood vessels, lymphatics, nerves
84
Q

which cells are found in the dermis?

A 
mainly fibroblasts
macrophages
mast cells 
lymphocytes
Langerhans cells
85
Q

which fibres are found in the dermis?

A

collagen - more common

elastin - less common but very important

86
Q

what is ground substance?

A

a jelly like mass of mucopolysaccharides & glycosaminoglycans

87
Q

what do fibroblasts do?

A

make collagen;

pro-collagen is made first which is cleaved by enzymes to make collagen

88
Q

what does collagen do?

A

becomes fixed in the dermal layer & gives strength to it

89
Q

what does elastin do?

A

gives the skin elasticity

90
Q

what do macrophages do?

A

they are immune scavengers & Ag presenters

91
Q

what do Langerhans cells of?

A

Ag presentation

92
Q

what are mast cells?

A

chemical messengers

93
Q

what happens to skin in ageing?

A
  • elastin fibres become less well formed
  • collagen gets depleted
  • fibroblasts & DEJ become much flatter
  • there are less nutrients being delivered to the epidermis
94
Q

what makes ageing worse?

A

UV light & smoking

95
Q

how is blood transported to the skin?

A

arteriole-> precapillary sphincters -> arterial capillaries -> venous capillaries -> post capillary venules -> collecting venules
(more blood delivered than metabolic need)

96
Q

why is the surface of the epidermis undulating?

A

for a greater surface area

97
Q

what does a localised overgrowth of blood vessels cause?

A

port wine stain, “stork marks”
often on face
can be liked to epilepsy
pretty harmless

98
Q

how is lymph drained from the skin?

A

through sub-epidermal meshed networks from smaller non-contractile vessels to larger contractile lymphatic trunks

99
Q

what are the important immune functions of the lymphatics?

A
  • immune surveillance by circulating lymphocytes and Langerhans cells
  • channelling of micro-organisms / toxins
100
Q

how do lymphatics run?

A

they mirror the blood supply

101
Q

how is chronic lymphoedema caused & treated?

A

caused by a variety of things e.g. blockage/lack of lymph nodes or infection damaging lymph vessels
squeeze leg with bandages but skin is irreversibly damaged for life

102
Q

which somatic sensory nerves are found in the skin?

A
  • free nerve endings

- special receptors: pacinian (pressure) & meissners (vibration) copuscles

103
Q

describe messiness’ corpuscles

A

sense light touch

found in fingertips & lips

104
Q

what do free nerve endings detect?

A

pain

105
Q

what do motor nerves do in the skin?

A

innervate sweat glands

106
Q

describe pacinian corpuscles

A

onion shaped nerve ends that detect deep pressure

107
Q

what is neurofibromatosis?

A

overgrowth of nerve ending which are abnormally thickened

benign growths unless affecting brain or spine

108
Q

name the 3 types of skin glands

A

eccrine
sebaceous
apocrine

109
Q

when are eccrine glands stimulated & where are they?

A

stimulated when the body is working hard

found over the whole skin surface, particularly on palms, soles & axillae

110
Q

where are sebaceous glands usually found?

A

often found linked to hair follicles, widely distributed across body mostly on face & chest
are hormone sensitive

111
Q

what does the over stimulation of a sebaceous gland cause?

A

acne

112
Q

where are apocrine glands found & what do they do?

A

found in the perineum & axillae

secrete odours containing pheremones

113
Q

what do sebaceous glands produce?

A

sebum: squalene, wax esters, triglycerides & free fatty acids

114
Q

what are the functions of a sebaceous gland?

A

control moisture loss & protect against bacterial & fungal infection

115
Q

what can hair follicles do if the skin is damaged?

A

they can repopulate the top part of the skin using the epithelium in the hair follicle

116
Q

how do apocrine sweat glands develop?

A

as part of the pilosebaceous unit

117
Q

how are apocrine glands stimulated?

A

by androgen

118
Q

how are eccrine glands controlled?

A

by sympathetic cholinergic nerve supply in response to mental, thermal & gustatory stimulation

119
Q

what functions do eccrine glands have?

A

can perform ultrafiltration
cooling by evaporation
moisten palms & soles to aid grip

120
Q

where do eccrine glands secrete to?

A

directly onto skin surface

121
Q

name some of the functions of the skin (at least 3)

A
  • barrier function
  • metabolism & detoxification
  • thermoregulation
  • immune defence
  • social communication
  • sensory functions
122
Q

give an example of acute skin failure

A

toxic epidermal necrolysis

123
Q

what can cause erythoderma?

A

dermatitis
psoriasis
drug reaction
T cell problmes

124
Q

what is erythoderma?

A

inflammatory skin disease with erythema and scaling that affects nearly the entire cutaneous surface. causes a loss of water from the skin.

125
Q

what does skin failure do in terms of the barrier function?

A

fluid loss -> dehydration
protein loss -> hypoalbuminaemia
infection

126
Q

what does skin failure do in terms of thermoregulation?

A

heat loss -> hypothermia

127
Q

what does skin failure do in terms of immune defence function?

A

spread of infection

128
Q

what does skin failure do in terms of the metabolic function?

A

disordered thyroxine metabolism

129
Q

what does skin failure do in terms of the communication function?

A

inability to display healthy skin -> stigma

130
Q

what does skin failure do in terms of the sensation function?

A

pain sensation working -> pain

131
Q

what is the skin a barrier to?

A

physical factors: friction, mechanical trauma UV radiation
chemical factors: irritants, allergens, toxins
pathogens: bacteria, viruses, fungi

132
Q

name the 4 stratum layers of the skin, top to bottom

A

stratum corneum
stratum granulosum
stratym spinosum
stratum basale

133
Q

how does our skin protect us from UV radiation?

A

melanin pigment formed in basal cells absorbs UV rays to protect DNA in the cell’s nuclei

134
Q

how is the skin metabolically active?

A

Vit. D metabolism

Thyroid hormone metabolism

135
Q

what is the detoxification function of the skin?

A

defence against chemicals, drugs, pollutants & sunlight

136
Q

where is Vit. D3 stored?

A

as hydroxycholecalciferol in the liver

137
Q

what is hydroxycholcalciferolconverted to?

A

1,25-dihydroxycholecaliferol in the kidney

138
Q

how is Vit. D metabolised?

A

UV light stimulates the conversion of cholecalciferol to Vit. D3

139
Q

how is thyroid hormone metabolised?

A

thyroxine to triiodothyronine

140
Q

where does thyroid hormone metabolism occur?

A

mostly in the peripheral to the thyroid tissues including skin
some occurs in thyroid glands

141
Q

how is temperature sensed?

A

through thermoreceptors

142
Q

describe how the superficial & deep plexuses of blood vessels help with temperature control

A

depending on how much going through each decides how much heat you lose from the skin
e.g. central body temp too high, more blood flow through superficial plexus

143
Q

what is eczema herpeticum?

A

disseminated herpes simplex virus infection

144
Q

what are the sensory functions of the skin?

A

touch, pressure, vibration, pain, itch, heat, cold

Dermatology (16 decks)

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