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week 1 > Skin Structure And Function > Flashcards

Skin Structure And Function Flashcards

1
Q

What are the 3 main layers of the skin

A

Epidermis
Dermis and
Subcutis/hypodermis

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2
Q

Briefly explain the epidermis ?

A

Self regenerating
Stratified squamous epithelium
Produces non living surface layer of the protein keratin
Direct contact with external environment

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3
Q

Is the epidermis water resistant ?

A

Yes

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4
Q

The main cells involved in the epidermis are called what ?

A

Keratinocytes

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5
Q

What are the different layers of the epidermis starting from deepest

A

Stratum basale -> stratum Spinosum -> stratum granulosum -> stratum Corneum

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6
Q

Explain thee basement membrane ?

A

Separates the epidermis from the dermis
Stratum basale attached to it by hemidesmosomes

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7
Q

What does the stratum basale layer look like

A

Cuboidal/low columnar cells
Attached to the basement membrane by hemidesmosomes
Basal cells have highly indented+ folded basal cell membrane with numerous hemidesmosomes

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8
Q

What is the function of the stratum basale ?

A

Contain stem cells
Mitotically active/ proliferates continuously
Allows maturation to renew/regenerate other layers
Basal cells -> mature into stratum spinosum

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9
Q

Explain the stratum spinosum

A

Prickle cell layer
Multilayered
Contains polyhedral shaped keratinocytes - these synthesise cytokeratins

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10
Q

What are cytokeratins ?

A

Cytoplasmic intermediate filaments which accumulate to form tonofibrils

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11
Q

What are tonofibrils ?

A

Bundles of tonofilaments
Tonofibrils bind to desmosomes to form strong contact between adjacent keratinocytes

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12
Q

Why is the stratum spinosum called the prickle cell layer

A

Due to the desmosome junctions which are seen as prickles or spines

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13
Q

What do the keratinocytes mature into from the stratum spinosum ?

A

The stratum granulosom - granular layer

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14
Q

What occurs to the keratinocytes in the granular layer ?

A

Cells become flattened
Contain basophillic keratohyalin granules

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15
Q

What is the function of keratohyalin granules ?

A

Contain amino acids and protein that interact with tonofibrils which produces keratin -> keratinisation

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16
Q

What happens with cells in the stratum granulosum

A

Cells start to lose their nucleus and cytoplasm and become the stratum corneum

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17
Q

Explain the stratum corneum ?

A

Keratin squames -> large flat plate like envelopes filled with cross linked keratin

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18
Q

Why is the stratum corneum water resistant

A

Due to lipids
Lipid containing anti wetting agents synthesised

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19
Q

Where is stratum lucidum found ?

A

Only in thick skin

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20
Q

What can the epidermis do ?

A

Self renew

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21
Q

Where does skin regeneration start ?

A

Stem cells in the basal layer continuously divide and differentiate migrating upwards

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22
Q

Explain the maturation of keratinocytes ?

A

1.Cells start process of differentiation in basal layer
2. Differentiating cells pushed upwards into stratum spinosum (produce prickle cells)
3.cell shape changes as this occurs and desmosomes become more pronounced
4.prickle cells continue to be pushed upwards and reach granular layer
5.cells degraded - loses nucleas and cytoplasm
6. Highly keratinised flattened cell
7.corneocytes - eventually shed off and die

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23
Q

What is the thickness of skin related to ?

A

The dermis and subcutis

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24
Q

What is the dermis composed of ?

A

It is connective tissue
Composed of collagen I
and elastin fibres and ground substance

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25
Q

What are the main cells found in the dermis ?

A

Fibroblasts

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26
Q

What are the main functions of the dermis ?

A

Immune role
Provides a blood supply
Tensile strength -> collagen
Allows stretch -> elastin

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27
Q

What are the to layers of the dermis ?

A

Superficial papillary dermis
Deep reticular dermis

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28
Q

Explain the structure of papillary dermis ?

A

Contain fine, interlacing collagen and elastic fibres
Also contain blood vessels and nerve endings

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29
Q

Explain the structure of the reticular dermis ?

A

Thicker layer -> collagen binds much more strongly
Elastin fibres much thicker too ad longer

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30
Q

What is the dermis epidermal junction ?

A

Attachment of epidermis to dermis through hemidesmosomes
It aligns cells of the epidermis

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31
Q

What is function of the dermo-epidermal junction

A

Serves as a base for repithelialisation in wound healing
Barrier function -> from and into epidermis

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32
Q

Explain the subcutis

A

Mostly composed of adipose tissue
Compartmentalised by vertical fibrous septa

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33
Q

What is the use of subcutis

A

Fatty layer of the skin
Acts as energy source
Shock absorption and insulation

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34
Q

How does the skin act as a sensory organ

A

It has free nerve endings in the skin

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35
Q

What is the function of the free nerve endings ?

A

Occupy the papillary dermis and extend into epidermis where they associate with Merle cells and act as mechanoreceptors

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36
Q

What are meisnners corpuscles

A

Rapidly acting mechnoreceptors which are responsible for touch
Prominent in papillary dermis of hands and feet

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37
Q

What are pacinian corpuscles ?

A

Detect deep pressure and vibration

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38
Q

Where are pacinian corpuscles found ?

A

Deep into subcutis

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39
Q

What are examples of adnexal structures ?

A

Hair and nails and glands

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40
Q

What is hair

A

Long thin cylinderal shafts composed of keratin

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41
Q

What is the function of hair and fur?

A

Providing colour and shape but particularly thermoregulation -> heat conservation

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42
Q

What is the hair follicle ?

A

Tubular structure of specialised connective tissue and epithelium

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43
Q

How is a hair follicle reduced ?

A

During active hair growth the epithelial cells around the hair papilla proliferate to form layers of the follicle

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44
Q

What gives hair their colour ?

A

Melanocytes
As melanin is incorporated in cells that form hair shaft

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45
Q

What causes hair to stand up ?

A

Contraction of the arrest or pili smooth muscle -> thermoregulated response

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46
Q

Explain the structure of the nail briefly

A

Dense keratinised plate which rests on stratified squamous epithelium - ‘the nail bed’

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47
Q

How do nails grow ?

A

Proliferation and differentiation of the epithelium underlying the nail root

48
Q

What is the role of the eccrine glands ?

A

Temperature control glands -> excrete sweat and therefore lower body temperature

49
Q

Where are eccrine glands found ?

A

Everywhere on human skin part from nail beds, lips, external auditory canal and some parts of the genitalia
Most abundant -> palms, soles and axillae

50
Q

What are the role of the apocrine glands ?

A

Scent glands - role unclear in humans

51
Q

Where can the apocrine glands be found ?

A

Axillae and genitals

52
Q

What are sebaceous glands and their function

A

Formed from hair follicle
Produce sebum- lipid which can lubricator the skin
Greatly enlarge at puberty in response to androgens

53
Q

Where can sebaceous glands be found ?

A

Everywhere except palms and soles

54
Q

Label the skin

A
55
Q

What are the cells in the dermis ?

A

Fibroblasts
Lymphocytes
Dermal dendritic cells
Mast cells

56
Q

What are common cells in the epidermis ?

A

Keratinocytes
Stem cell
Merkel cell
Langerhans cell
Melanocytes

57
Q

Where can keratinocytes be found ?

A

Keratinised stratified squamous epithelium

58
Q

Where can keratinocyte be found ?

A

Protection and barrier
Involved with melanocytes in vitamin d function

59
Q

Where can stem cells be found ?

A

Stratum basale

60
Q

What is the function of stem cells ?

A

Self renewal and repopulation of epidermal layers
Allow skin regeneration and cell turnover

61
Q

Where can merkel cells be found ?

A

Epidermis

62
Q

What is the function of touch cells ?

A

Touch cells
Relay touch related information

63
Q

Where can Langerhan cells be found ?

A

Epidermis
Stratum spinosum and upper dermal layer

64
Q

What is the function of langerhans cell

A

Antigen presenting cells
Allow phagocytosis

65
Q

Where can melanocytes be found ?

A

Basal layer

66
Q

What is the function of melanocytes

A

Protection from radiation
For example ultraviolet light
Provide colour to skin and hair

67
Q

How do melanocytes protect from uv radiation ?

A

Melanin produced from tyrosine within melanosomes -> transferred to keratinocytes
Form cap over nucleas protecting the dna

68
Q

What is uv radiation implicated in ?

A

Development of melanoma and non melanoma skin cancers

69
Q

What can chronic uv exposure in humans lead to ?

A

Loss of skin
Abnormal pigmentation
Haemorrhage of blood vessels
Wrinkles + premature ageing

70
Q

What is vitamin d useful for ?

A

Vitamin d synthesis

71
Q

How is vitamin d produced

A

255-330nm UVB converts 7-dehydrocholesterol in the plasma membrane of keratinocytes to pre vitamin D3

72
Q

How do melanocytes and keratinocytes work together to protect cells from UV damage

A
  1. Melanin in synthesised by melanocytes within organelles called melanosomes
  2. Melanosomes transferred into neighbouring keratinocytes By melanocytes cytoplasmic processes
  3. Melanosomes with keratinocyte -> a cap is formed over nucleus which forms protective layer over the dna
73
Q

Where are keratins found

A

All epidermal layers

74
Q

What is the function of keratins ?

A

Major structural protein
Intermediate filaments

75
Q

What molecules are found in keratohyalin molecules ?

A

Profilaggrin
Involucrin
Loricrin

76
Q

What is the function of profilaggrin

A

Converted to fillaggrin -> aggregates keratin filaments into tight bundles

77
Q

What is the function of involucrin?

A

Formation of cell envelope around cells in the stratum corneum

78
Q

Where is the function of loricrin

A

Cross links to involucrin

79
Q

What molecules form the lamellar granules

A

Polysaccharides
Glycoproteins
Lipids

80
Q

What is the function of the polysaccharides+ glycoproteins and lipids in the lamellar granules

A

Form the cement that holds together the stratum corneum cells -> impermeable intracellular lipid layer

81
Q

What is the function of fibroblast

A

Synthesis of collagen,elastin + other extra cellular matrix compounds -> involved in sending and receiving signals from other molecules

82
Q

What is the function of lymphocytes

A

Immunosurveillance -> detecting foreign antigens

83
Q

What is the function of dermal dendritic cells

A

Phagocytosis
Antigen presentation

84
Q

What is the function of mast cells

A

Produce inflammatory mediators such as histamine or heparin
For eosinophils and neutrophils
Important in wound healing - immediately released after injury

85
Q

What is collagen type 1

A

Major structural fibrous protein - provide tensile strength

86
Q

What is the function of elastin

A

Confer elasticity and recoil -> allow stretch and recoil in response to movement

87
Q

What do proteoglycans and glycosaminoglycans provide

A

Hydration

88
Q

What are the key molecules in the dermis

A

Collagen type I - stronger than type III
Elastin
Proteoglycans
Glycosaminoglycans

89
Q

What is a wound

A

The breakdown in the protective function of the skin

90
Q

A wound causes the loss of what thing ?

A

The loss of continuity of epithelium

91
Q

What is the depth of injury related to ?

A

The ability to heal

92
Q

Describe what would mean by erosion wound

A

Only epidermis lost - healing faster

93
Q

What would mean by ulceration ?

A

Wound deep into epidermis

94
Q

What is partial thickness wound

A

Epidermis and varying parts of dermis are damaged

95
Q

In a partial thickness wound what acts as a reservoir of epithelial cells

A

Adnexal structures because they allow repopulation of the wound

96
Q

What is a full thickness wound ?

A

Epidermis
All of dermis
Deeper structures affected
Wound edge cells only

97
Q

What are the three phases of wound healing

A

Inflammatory
Proliferation
Remodelling

98
Q

Explain the inflammation phase ?

A

1.Platelets initiate haemostasis/blood clot and healing cascade
2. Attracts other cells to. The wound to fight infection and transition from inflammation to repair 3. Neutrophils and macrophages phagocytose dead tissue and bacteria/pathogens

99
Q

What are the characteristic of inflammation ?

A

Red/swelling

100
Q

Explain the proliferative phase

A

1.Reepithelialisation
2. Formation of granulation tissue mainly type III collagen
3. Neovascularisation occurs : proliferation and migration of endothelial cells occur

101
Q

Explain what reepithelisation is

A

1-2 days of wounding
Epithelial cells loosen cell to cell adhesions and migrate to the wound site, cover the granulation tissue and then meet in the middle
2. Once wound is covered in keratinocytes - keratinocytes start to proliferate

102
Q

Explain simply what reepithelisaton is

A

Cells dividing to replace damaged or loss of cells

103
Q

What are the two methods of keratinocyte migration

A

Leapfrog method
Train method

104
Q

How is collagen type III formed when granulation tissue is formed

A

Underneath cells fibroblasts are recruited that replace collagen

105
Q

What is the remodelling phase

A

When granulation tissue becomes mature tissue

106
Q

How does remodelling phase occur

A

Collagen is organised into thick bundles
Cross linked -> forms mature scar
Switch in type of collagen

107
Q

What is the switch in collagen in te remodelling phase

A

Type III to type I

108
Q

Compare type I collagen to type III collagen

A

Type I collagen is much more organised and stronger

109
Q

Explain the strength of the skin

A

Final -> only 70-80% of preinjured skin
And after 1 year
Strength is 5% at 1 week 20% at 3 weeks

110
Q

How do cells in wound healing know what to do ?

A

They respond to signalling molecules

111
Q

What is the function of epidermal growth factor

A

Allows reepithelialisation -> proliferation and maturation of keratinocytes

112
Q

What is the function of platelet derived growth factor

A

Matrix formation -> activates increased numbers and activity of fibroblasts
Also important in remodelling due its role in production of proteases

113
Q

What is the function of vascular endothelial growth factor

A

Angiogenesis which is endothelial cell proliferation and migration

114
Q

Which 3 signalling molecules are involved in inflammation

A

Interleukin -1 (II-1)
Interleukin-6 (II-6)
Tumour necrosis factor

115
Q

What do epidermal growth factors do in terms of keratinocytes

A

Signal to the keratinocytes to divide and migrate to close over the wound

116
Q

What are local factors that’s affect wound healing

A

Infection
Foreign body
Oxygenation - cells highly active need o2 for respiration
Vascular supply

117
Q

What are systemic factors that’s defect wound healing

A

Age
Diseases
Alcohol and smoking
Immunocomprimised conditions
Obesity - affects vascular flow
Medications

week 1 (6 decks)

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