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LR Dermatology > Skin Structure & Function > Flashcards

Skin Structure & Function Flashcards

1
Q 
What cells of the embryo do the...
- epidermis
- dermis
- melanocytes 
... originate from?
A
  • Epidermis = single layer of ectoderm cells (periderm)
  • Dermis = mesoderm (below ectoderm)
  • Melanocytes = neural crest
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2
Q

What are the 4 layers of the epidermis?

A

Basal layer
Prickle cell layer
Granular layer
Keratin layer

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3
Q

Give 4 examples of appendages in the epidermis

A

Melanocytes
Sebaceous glands
Arector pili muscles
Hair follicles

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4
Q

What are Blaschko’s lines?

A

Developmental growth patterns of the skin due to migration of the cells from the centre to the outside of the foetus during development

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5
Q

How can Blaschko’s lines signify a congenital problem?

A

If the daughter cell of the line is affected, all migrating/ descending cells along the line will also be affected

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6
Q

What is found between the dermis and epidermis?

A

A basement membrane called the dermo-epidermal junction

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7
Q

What is the…
- dermis
- subcutis
… mainly composed of?

A

Dermis - connective tissue

Subcutis - fat

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8
Q

The dermis is thicker/thinner than the epidermis

A

Thicker

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9
Q

What is the epidermis mainly composed of?

A

Composed of stratified squamous epithelium - 95% is keratinocytes

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10
Q

How thick is the epidermis?

A

~ 1.5mm

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11
Q

What is epidermal turnover regulated by?

A

Growth factors
Cell death
Hormones

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12
Q

Loss of regulation of epidermal turnover can lead to…

A

Skin cancer

Psoriasis

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13
Q

How long does it usually take for skin cells to differentiate and migrate from the basement membrane to the keratin layer?

A

Around a month/ 28 days

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14
Q

Describe the basal layer of the epidermis

A
  • Small cuboidal cells
  • Usually 1 cell thick
  • Contains lots of keratin (intermediate filaments)
  • Highly metabolically active
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15
Q

Describe the prickle cell layer of the epidermis

A
  • Larger polyhedral cells
  • Lots of cell-to-cell connections (desmosomes) allow them to migrate up the epidermis
  • Intermediate filaments connect to desmosomes
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16
Q

Describe the granular layer of the epidermis

A
  • 2-3 layers of flatter cells
  • The cell nuclei is lost
  • Contain large granules containing filaggrin and involucrin proteins
  • Contain Odland bodies (which process lipids)
  • High lipid content
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17
Q

What is the function of filaggrin and involucrin proteins in the granular layer?

A

The proteins are released from the granules and are cut into amino acids

These amino acids bind water molecules to prevent water from leaving the body

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18
Q

What would happen in the absence of filaggrin proteins from the granular layer?

A

Water would be able to leave the body and the skin would become very dry

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19
Q

What is the No.1 risk factor for eczema and atopic dermatitis?

A

Absence of filaggrin proteins

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20
Q

Describe the keratin layer of the epidermis

A
  • Corneocytes (overlapping non-nucleated cell remnants) form an insoluble cornified envelope
  • 80% keratin & filaggrin
  • Lamellar granules release lipids
  • Forms a tight waterproof barrier
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21
Q

Which layer of the epidermis is most commonly affected by skin conditions?

A

The keratin layer

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22
Q

The subcutis/? is mostly composed from ?

A

Hypodermis

Fat

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23
Q

What is the function of fat in the subcutis?

A
  • Energy storage

- Movement of the skin

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24
Q

What is panniculitis?

How does it relate to skin conditions?

A
  • Panniculitis = infection of fat

- It restricts skin movement

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25
Q

What is acne caused by?

A

Bacteria that clog the hair shafts and feed on fatty acids/ grease produced by the sebaceous glands

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26
Q

95% of epidermal cells are keratinocytes.

Name 3 other epidermal cells

A
  • Melanocytes
  • Langerhans cells
  • Merkel cells
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27
Q

What are melanocytes?

Where are they found?

A
  • Pigment producing dendritic cells

- Found in the basal layer and above (basal & suprabasal)

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28
Q

Where do melanocytes originate from during foetal development?

A

Migrates from the neural crest to the epidermis in the first 3 months of development

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29
Q

How do melanocytes produce pigment?

A

They contain melanosomes that produce melanin pigment

Dendrites pass full melanosomes to adjacent keratinocytes

Melanin is distributed evenly over the keratinocytes to give the skin colour

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30
Q

What is another function of melanocytes? (besides pigmentation)

A

They form a protective cap over the nucleus of the cells in the basal layer of the epidermis

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31
Q

Which hormone stimulates melanocyte production?

A

Alpha melanocyte stimulating hormone = alpha-MSH = ACTH

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32
Q

What is vitiligo?

A

An autoimmune disease characterised by loss of melanocytes (patches of white skin in a brown-skinned person)

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33
Q

What is albinism?

A

A genetic condition characterised by partial loss of pigment production

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34
Q

The immune system can kill melanocytes - this can be taken advantage of to help fight malignant melanomas.
Why can stimulating the immune system like this lead to further problems?

A

Stimulating the immune system to kill the melanocytes can lead to other autoimmune diseases e.g., vitiligo

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35
Q

What are langerhans cells and where are they found?

A

Dendritic cells found in the prickle cell layer of the epidermis (suprabasal)

(Also found in the dermis and lymph nodes)

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36
Q

What do langerhans cells do?

A

They are involved in the skin immune system as antigen presenting cells (dendrites!)

They pick up antigens (e.g., microbes) and circulate to lymph nodes

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37
Q

What are Merkel cells?

A

Mechanoreceptors in the epidermis

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38
Q

How do Merkel cells allow us to experience touch?

A

They are connected to nerve endings which are connected to the CNS

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39
Q

Where are Merkel cells found in the epidermis?

A

The basal layer (basal)

40
Q

Describe Merkel cell cancer

A
  • Rare
  • Caused by viral infection
  • Very high mortality - nearly all patients die
41
Q

Name the components that make up the structure of hair follicles (pilo-sebaceous units)

A
  • Dermal papilla of hair follicle
  • External and internal root sheaths
  • Cortex
  • Medulla
  • Hair shaft
  • Sebaceous glands
  • Arrector pili muscle
42
Q

Describe the embryological development of hair

A
  • Hair bud branches from the epidermis
  • Hair shaft grows from the bud
  • Hair papilla comes from the dermis
  • Smooth muscle fibres join to form arrector pili muscle
  • Sebaceous gland develops
43
Q

What do the sebaceous glands do?

A

Produce a fatty oil (sebum) that is released onto the skin

44
Q

What do arrector pili muscles do?

A

Contract to lift the hairs when it is cold

45
Q

Describe the cycle of hair follicle growth (3 steps)

A
  • Anagen -> growing
  • Catagen -> growth stops and the outer root sheath shrinks i.e., the hair is starting to die
  • Telogen -> shedding phase, the hair remains in the follicle but comes out easily
46
Q

Why does different people’s hair grow at different rates?

A

The length of the anagen (growing) phase can vary from weeks to years

47
Q

What stage of the hair follicle growth cycle are most hairs in?

A

Anagen (90%)

The other 10% are in telogen

48
Q

How long are hair follicles in catagen for?

A

Around a month for most people (3-4 weeks)

49
Q

What are the functions of the dermo-epidermal junction aka basement membrane?

A
  • Anchors epidermis to dermis (support)
  • Growth and differentiation of basal cells
  • Semi-permeable membrane acts as a barrier and filter for proteins to filter across to the epidermis
50
Q

What are the 3 layers of the dermo-epidermal junction? (from top to bottom)

A
  • lamina lucida
  • lamina densa
  • sub-lamina densa zone
51
Q

Give 2 examples of diseases targeting the dermo-epidermal junction

A
  • Bullous pemphigoid (autoimmune disease)

- Epidermolysis bullosa (rare inherited disorder involving defects in DEJ proteins)

52
Q

What is the function of the dermis?

A

It is a connective tissue support structure for the skin

53
Q

List the components of the dermis

A
  • Ground substance
  • Cells (fibroblasts, macrophages, lymphocytes, langerhans cells)
  • Fibres (collagen and elastin)
  • Muscle, blood vessels, lymphatics, nerves
54
Q

What is the function of fibroblasts?

A

Production of collagen and elastin fibres

55
Q

Why do individuals with darker skin tend to ‘age better’?

A

Thicker collagen in darker skin offers more protection and more macrophages

56
Q

The papillary dermis is above/below the reticular dermis

A

Above

57
Q

What is the difference between intrinsic and extrinsic skin aging?

A
  • Intrinsic skin ageing happens to everyone

- Extrinsic skin ageing is more pronounced in sun lovers and smokers

58
Q

What is the difference between hypertrophic and atrophic photoaging?

A

Hypertrophic -> deep furrows and leathery appearance

Atrophic -> thin, smooth appearance

59
Q

Describe the structure of blood vessels in the dermis

A

Vessels in the subcutis form horizontal plexuses in the dermis

These reach up to supply the epidermis

60
Q

Why does the dermis have a blood supply greater than its metabolic needs?

A

The vessels also supply the epidermis

61
Q

What is angioma?

A

Benign dilatation of the blood vessels in dermal tissue

These are friable and bleed easily

62
Q

Where are lymphatic vessels of the skin found?

A

As meshed networks in the dermis

63
Q

What are the functions of lymphatic vessels in the skin?

A
  • Drain cell debris
  • Drain toxins/ pathogens
  • Take part in immune surveillance via circulating lymphocytes and Langerhans cells
64
Q

Give 3 examples of somatic sensory nerves found in the dermis

A
  • Free nerve endings in the higher dermis (touch)
  • Pacinian corpuscles in the deep dermis (specialised pressure receptors)
  • Meissners corpuscles in the deep dermis (specialised vibration receptors)
65
Q

In the dermis, what do the autonomic nerves supply?

A
  • Blood vessels
  • Nerves
  • Glands
66
Q

In a biopsy, Pacinian corpuscles look like…

A

Onion rings

67
Q

What are the 3 main segments of a hair follicle?

A
  • Infundibulum (upper part)
  • Isthmus (where sebaceous glands join and stem cells are located)
  • Hair bulb (where the papilla is found)
68
Q

The arrector pili muscle gets its nerve supply from…

A

The sympathetic nervous system

69
Q

African individuals have strong/fragile hair

A

Fragile

70
Q

Hairs in anagen are hard/easy to pull out

A

Hard

71
Q

What is the most common hair loss condition?

A

Alopecia areata

an autoimmune disease targeting patches of hair papilla, hair isthmus isn’t targeted so hair can grow back

72
Q

What is hirsutism?

A

Inappropriate growth of hair (in women) -> can be physiological or caused by excess androgen hormones

73
Q

What are the 3 skin glands found in the dermis?

A
  • Sebaceous
  • Apocrine
  • Eccrine
74
Q

Describe sebaceous glands

A
  • Start producing an oily sebum during puberty
  • Holocrine secretions sent into pilary (hair) canal
  • Found everywhere but the palms and soles
  • Largest glands in the face, chest and upper back
  • Function is to control moisture loss and protect from fungal infection
  • Can lead to acne if they produce excess sebum
75
Q

Describe apocrine sweat glands

A
  • Empties oily fluid into pilary (hair) canal
  • May be involved in sex hormone secretion but function is unknown
  • Androgen dependent
  • Found in the axillae, groin, eyelids, ears, mammary and perineal regions
76
Q

Describe eccrine sweat glands

A
  • These are the true sweat glands
  • Found on all skin surfaces except lips and genitals
  • Functions include cooling by evaporation and moistening of the palms and soles for gripping
  • Sympathetic supply can be stimulated by mental, thermal or taste cues
77
Q

What are the 6 main functions of the skin?

A
  • Barrier function
  • Metabolism & detoxification
  • Thermoregulation
  • Immune defence
  • Communication
  • Sensory functions
78
Q

What may the skin be a barrier against?

A
  • Physical: trauma, friction, UV radiation
  • Chemical: irritants, allergens, toxins
  • Pathogens: bacteria, viruses
79
Q

How do melanocytes help protect against UV radiation?

A

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

80
Q

Give 2 examples of metabolism via the skin

A
  • Ultraviolet B acts on a precursor (7-dehydrocholesterol) to produce vitamin D3 in the skin
  • Thyroid hormone T4 is converted to more metabolically active T3
81
Q

How is the skin involved in thermoregulation?

A
  • Protects against heat and cold via sweating and vasodilation/contraction
  • Warm/ cold thermoreceptors
82
Q

When the body is too hot, the superficial/deep vascular plexus in the dermis will be more dilated

A

Superficial (to lose heat)

83
Q

When the body is too cold, the superficial/deep vascular plexus in the dermis will be more dilated

A

Deep (to conserve heat)

84
Q

How is the skin involved in immune defence?

A
  • Non-specific responses e.g., itching to remove a parasite

- Specific cellular immune responses (see immunology)

85
Q

Why is the skin thought to be involved in communication between individuals?

A

Skin colour, smell, anomalies and level of exposure influence how other people view an individual

86
Q

What different sensory functions does the skin have?

A

Touch, pressure, vibration, pain, itch, heat, cold

87
Q

What is meant by the pilosebaceous unit?

A

The hair follicle and the surrounding accessory appendages

88
Q

What is bullous pemphigoid?

A

An autoimmune disease which targets proteins in the dermo-epidermal junction, resulting in the formation of blisters

89
Q

Describe the structure of the nails:

  • Nail plate =
  • Matrix =
  • Cuticle =
  • Hyponychium =
A
  • Nail plate = plate of cells filled with hard keratin sit on the nail bed
  • Matrix = found beneath the nail and epidermis, cells divide then produce hard keratin
  • Cuticle = extension of the skin fold covering the nail root
  • Hyponychium = secures the free nail edge
90
Q

What is the difference between primary and secondary intention wound healing?

A

Primary wound healing -> the edges of the wound are connected, e.g., by a suture, usually resulting in more rapid wound healing

Secondary wound healing -> the edges of the wound cannot practically be joined together so the wound is left open to heal on its own

91
Q

What are the 3 stages of wound healing?

A
  1. Inflammation - platelets form initial clot, leucocytes phagocytose bacteria
  2. Proliferation - granulation tissue forms, fibroblasts lay down matrix and contract wound, angiogenesis occurs
  3. Tissue remodelling - new tissue becomes scar tissue as fibroblasts lay down collagen
92
Q

What is the difference between the appearance of superficial and deep burns?

A

Superficial - erythematous, wet, painful, blistering

Deep - white or black/charred, dry, numb

93
Q

Which layers of the skin are affected by 1st-3rd degree burns?

A

1st -> epidermis
2nd -> epidermis and dermis
3rd -> extends beyond the dermis (full thickness burn)

94
Q

What factors can delay wound healing?

A
  • Infection
  • Poor arterial supply
  • Poor venous return
  • Repeated trauma/friction
  • Poor nutrition
  • Underlying disease e.g., diabetes, anaemia
95
Q

What are the 4 stages of pressure sore development?

A
  1. Skin is unbroken but reddened and tender
  2. Skin is swollen and blisters may be present
  3. Sore breaks through the skin and crater-like ulcers are present. The wound is prone to infection
  4. Sore extends deep into fat, muscle and bone tissue. Eschar may be seen
96
Q

What is eschar?

A

Blackened dead tissue in deep open wounds

97
Q

What do Odland bodies in the granular layer do?

A

Process lipids destined for the epidermal permeability barrier

LR Dermatology (11 decks)

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