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Jorge ENI > Skin Structure > Flashcards

Skin Structure Flashcards

1
Q

What are the layers of skin and their functions?

A

Epidermis - protect from dehydration
Dermis - tensile strength
Subcutis/hypodermis - energy storage as fat

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2
Q

Describe the embryological development of skin

A
  • one layer of ectoderm overlies a dermis of mesenchyme (mesoderm)
  • the ectoderm divides into the basal cell layer/stratum germinativum and the periderm (outer)
  • stratum intermedium fills the gap between these layers
  • further development leads to the adult structure (with the addition of melanocytes from the neural crest and Langerhans cells from bone marrow)
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3
Q

Describe embryological dermal development

A
  • increase in thickness and number of fibres
  • mesenchymal cells become fibroblasts
  • collagen fibres precede elastin fibres
  • ground substance (proteoglycans and hyaluronan)
  • development of nerves and BVs
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4
Q

Describe embryological development of the subcutis

A

Lipocytes develop in the 2nd half of gestation

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5
Q
A
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6
Q

What are cells of the epithelium call in skin?

A

keratinocytes

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7
Q

Label the epithelial layers of skin

A
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8
Q

Describe the embryological development of hair

A
  • Epidermal basal cells proliferate into dermis -> hair bud
  • aggregation of mesenchymal cells (dermal papilla) projects into tip of hair bud
  • epidermal cells grow around papilla -> hair bulb from which hair grows
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9
Q

Describe the components of a keratinocye

A

Adherens junctions (attach cell to cell)
Focal adhesions (attach cells to underlying dermis)
Keratins (intermediate-filament forming proteins that provide mechanical support)
Desmosomes (anchor keratinocytes together and provide intracytoplasmic signalling)
Hemidesmosomes (anchor the epidermis to the dermis)
Actin filaments

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10
Q

Give an example of a condition relating to keratin in the skin

A

Palmopalmar hyperkeratosis - genetic defect, causes splitting and pain in the epidermis of foot pads

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11
Q

Give an example of condition relating to the desmosomes in skin

A

Pemphigus foliaceus - immun-mediated disease with antibodies directed at desmosomes - prominent pustules

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12
Q

What are hemidesmosomes?

A

A strong link between keratin intermediate filaments and the interstitial collagen in the dermis

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13
Q

Give an example of a condition relating to hemidesmosomes

A

Epidermolysis bullosa acquisita - immune mediated disease with antibodies directed against collagen

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14
Q

Label this keratinocyte

A
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15
Q

Label the histology of haired skin

A
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16
Q
A
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17
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18
Q
A
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19
Q

What is the function of keratinocytes

A

Produce extracellular lipids (ceramides, cholesterols, fatty acids) from golgi apparatus in granular layer resulting in lipid lamellae
Immunologically active (not an innert barrier)

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20
Q

Describe the structure and function of the stratum basale

A

Single layer of cuboidal cells -
proliferative and anchoring
stem cell function (pluripotent)

Anchoring cells:
structural role - hemidesmosomes and desmosomes

Proliferative cells:
mitotically active - one cell remains as germinative cell and other differenitates

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21
Q

What is the stratum basale influenced by?

A

Growth factors and hormones e.g., epidermal growth factor, cortisol
Inflammatory mediators e.g., IL-1, IL-6
Drugs and vitamins e.g., vit D, retinoids

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22
Q

Describe the structure and function of the stratum spinosum

A

1-20 cells thick
polyhedral cells
prominent desmosomes
upper layer produced involucrin (part of cornified layer)

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23
Q

Describe the structure and function of then stratum granulosum

A

variably present in haired skin
slightly flattened cells
shrunken nuclei
various lipids and enzymes secreted extracellularly

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24
Q

Describe the structure and function of the stratum lucidum

A

Not present in haired skin (variably present in hairless, thickened skin)
Slightly flattened cells, shrunken nuclei
Increased intracellular lipids -> poorly stained

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25
Q

Describe the structure and function of the stratum corneum

A

Composed of anucleated flattened cells (squames)
Plasma membrane replaced by cornified envelope comprising intracellular proteins (Extensively cross linked)
Hydrophilic binding of lipids forms organised ‘mortar’ between sqaumes
desmosomes now called ‘corneodesmosomes’ (due to addition of corneodesmosin from stratum granulosum)

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26
Q

Describe the formation of the cornified envelope

A

In the upper granular layer, envoplakin and periplakin are laid on the cell membrane
Involucrin and TGM1 (transglutaminase 1) are added.
Ceramides are incorporated into the wall and fatty acids and cholesterol are released into intracellular space.
The cell membrane is replaced by a ceramide and fatty acid complex.

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27
Q

Give an example of a condition that effects the cornified layer

A

TGM1 mutation in Jack Russel Terriers -> severe hyperkeratosis

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28
Q

Describe the process of desquamation

A

Final part of terminal component
Homeostatic process - continual loss of cells
Destruction of the corneodesmosomes
Corneocytes fall off

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29
Q

Describe the structure and functions of the dermis

A

Connective tissue of mesenchymal origin:
- insoluble fibres (collagen and elastin) to give tensile strength
- soluble polymers (proteoglycans and hyaaluronan) to resist and absorb compressive forces
Contains epidermal appendages, arrector pili muscles, blood and lymph vessels and nerves

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30
Q

What are the cells present in the dermis

A

Macrophages
dermal dendritic cells
fibroblasts

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31
Q

Sensory nerves in the dermis

A

Respond to touch, pressure, temp, mociception, pruritus
Mechanoreceptors:
- free nerve endings (also in epidermis)
- rapid adapting: Meisseners and Pacinian corpuscles
- slow adapting: Merkel cells, Ruffini corpuscles

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32
Q

Motor nerves in the dermis

A

Adrenergic and cholinergic fibres
Arterioles, atrichial and epitrichial sweat glands

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33
Q

Describe the 3 layers of blood supply to the dermis

A

Deep dermal vascular plexus:
- interface of dermis and subcutis
- supply lower hair follicle and epitrachial sweat glands

Mid-dermal vascular plexus:
- level of sebaceous glands
- supply arrector pili muscles, mid hair follicles and sebaceous glands

Superficial dermal vascular plexus:
- just below epidermis
- capillary loops supply epidermis and upper hair follicle

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34
Q

What is the name for disease of the blood vessels

A

Vasculitis

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35
Q

Describe the structure and function of sebaceous glands

A

Differentiated from basal layer of germinative cells
Large, polygonal cells
Lots of vacuoles in the cytoplasm
Produce sebum (holocrine secretion) which is excreted via sqaumous duct to the hair follicle

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36
Q

Describe the components and function of sebum

A

Contains triglycerides and other lipids, transferrin, IgA, IgG
Functions:
- lubricated hair and skin
- required for normal hair shaft separation

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37
Q

Label this section of skin

A
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38
Q

Give an example of a condition that effects the sebaceous glands

A

Sebaceous adenitis - glands destroyed by disease -> scale, hair breakage and follicular casts

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39
Q

What are the 2 types of sweat gland

A

Epitrichial and Atrichial

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40
Q

Describe the structure and function of epitrichial sweat glands

A

Associated with a hair follicle
Single layer of flattened cuboidal cells surrounded by myoepithelial cells
Distributed throughout haired skin
Below sebaceous gland
Excrete sweat into piliary canal just above sebaceous gland opening
Not innervated

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41
Q

Describe the structure and function of atrichial sweat glands

A

Not associated with hair follicles
Single layer of flattened cuboidal cells surrounded by myoepithelial cells
Merocrine secretion
Small, tightly coiled
Innervated by cholinergic fibres

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42
Q

Label this section of skin

A
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43
Q

Name some specialised ‘atrichial’ glands

A

Mammary gland
Interdigital glands of small ruminants
External ear canal
Nasolacrimal glands
Apocrine glands of anal sac

44
Q

What types of hair are there?

A

Primary (guard hairs)
Secondary (downy hairs)

45
Q

What are hairs important for?

A

insulation
signalling
physical protection

46
Q

Describe the simple anatomy of hair

A

cortex, medulla and cuticle containing variable pigment

47
Q

What kind of hair follicles do omnivores and herbivores have?

A

Simple - each infundibulum has 1 hair shaft

48
Q

What kind of hair follicles do carnivores have?

A

Compound follicles

49
Q

Label this section of skin focusing on the hair

A
50
Q

Label this section of skin

A
51
Q

How do you distinguish between a growing and resting hair on a histological slide?

A
52
Q

Anagen definition

A

Actively growing hair

53
Q

Catagen definition

A

a period of rapid change in which the lower portion undergoes apoptosis

54
Q

Telogen definition

A

the hair is resting

55
Q

How many hairs does a simple follicle have?

A

1

56
Q

Describe compound hair follicles

A

Several hairs meet in follicular orifice
Primary (large hairs):
- bulb in deep dermis
- associated sebaceous, sweat glands and arrector pili muscles
Secondary (smaller hairs):
- not as deep in dermis
- may have sebaceous gland, but no sweat gland or arrector pili muscles

57
Q

Identify which type of compound hair follicles these are

A
58
Q

What is the best drink in the world

A

Huel daily greens

59
Q

Describe the process of anagen

A

New hair produced under previous hair in deep dermis
Distinctive hair bulb containing follicular dermal papilla

60
Q

Exogen definition

A

the process of hair being lost

61
Q

What is the isthmus in hairs

A

Where the sebaceous gland attaches
And the divide between the infundibulum and the inferior portion

62
Q

What type of hair growth do dogs, cats, horses and hedgehogs have?

A

Telogenic
Length is determined by duration of anagen and then they stop growing and rest

63
Q

How is hair cycle regulated?

A

photoperiod
temp
hormones (thyroid [+ve], growth hormone [+ve], oestrogen [-ve], corticosteroids [-ve])
Nutrition and general health
growth factors
drugs

64
Q

Describe the structure of anagen hairs

A

Found in the deep dermis
dermal papilla provide blood
hair bulb epithelium undergoes mitosis
melanocytes provide pigment
6 layers (inner to outer):
- medulla
- cortex
-cuticle
- huxley layer + henle layer (inner root sheath)
- outer root sheath (continuous with epidermis)
- basement membrane

65
Q

Label this hair

A
66
Q

What structures make up the inner root sheath?

A

Henle’s layer
Huxley’s layer
Cuticle

67
Q
A
68
Q

Describe the process of catagen

A

In the mid dermis:
- involution of the hair bulb and dermal papilla
- upward migration of the follicle and papilla
- loss of the internal root sheath
- develops a thick glass membrane (previously basement membrane) above the bulb of the follicle
Fast process mediated by apoptosis

69
Q

Describe the telogen phase

A

In mid to upper dermis:
- conical bulb at level of the attachment of the arrector pili muscle
- hair surrounded by external root sheath
- hair bulb separated from dermal papilla by thick basement membrane
- original bulb is dormant
- new bulb and papilla form beneath old follicle
- when stimulated, new bulb forms a new hair and the old hair is lost

70
Q

What stage of hair growth is this?

A

Anagen

71
Q

What stage of hair growth is this?

A

Telogen

72
Q

Describe the structure and function of vibrissae (sinus hairs)

A

Specialised hairs
Simple follicles with blood-filled sinuses between the inner and outer layers of the dermal sheath
nose, above eyes, lips etc.
Mechano/touch receptors

73
Q

Describe the structure and function of tylotrich hairs

A

Simple follicles in amongst body hairs
Mechanoreceptors (fast adapting)
Associated with tylotrioch pads (slow adapting)

74
Q

Label this diagram of the skin and hair follicle

A
75
Q

Label this skin histology

A

A – dermis
B – Stratum corneum
C – follicular osteum
D – sebaceous gland
E – sweat gland
F – hair bulbs
G - subcutis

76
Q

How does the skin provide photoprotection?

A

Nuclear capping by melanin prevents damage to basal cell nuclei
Urocanic acid in stratum corneum acts as natural sun screen
Skin thickness
Melanin absorbs UV

76
Q

How does the skin provide immunosurveillance?

A

Keratinocytes are immunologically active
Langerhans cells are APCs
T-cells and mast cells in the dermis
Antimicrobial proteins from keratinocytes and in sweat

77
Q

How does the skin regulate temp?

A

Altered blood flow in the superficial plexus allows regulation of the skin temp
Sweating
Hair is insulating

78
Q

What is the predominant cell type in the subcutis/hypodermis?

A

Lipocytes

79
Q

What is the function of lipocytes in the subcutis?

A

Energy reserve
Thermogenesis and insulation
Protective padding and support
Maintaining surface/contour shape

80
Q

What is the embryological origin of the subcutis?

A

mesenchymal origin

81
Q

How does the subcutis protect hair follicles, sweat glands and vessels?

A

Projects into dermis via papillae adiposae

82
Q

What are meloncytes?

A

Cells immersed in the epidermis with close contact with a defined number of keratinocytes via dendritic processes (forms an epidermal melanin unit/EMU)

83
Q

What are the 2 types of melanin

A

eumelanin - brown
phaeomelanin - reddish yellow

84
Q

What is the embryological origin of melanocytes?

A

Neural crest

85
Q

How do melanocytes cause pigmentation of skin?

A

they produce pigment in melanosomes which then transfer the pigment to keratinocytes

86
Q

Other than pigmentation, what are the functions of melanocytes?

A

photoprotection
immune function

87
Q

What is skin colour influenced by?

A

Genetics
UV light
Hormones/inflammatory mediators e.g., melanocyte stimulating hormone (MSH)

88
Q

Describe the structure and function of Langerhans cells

A

Tennis-racket or rod-shaped cytoplasmic organelle
APC
migrate to dermis and regional lymph nodes upon T-lymphocyte activation

89
Q

What is the relationship between infection and skin pigmentation?

A

Langerhans cells are markedly reduced in UV light
Increased infection on white areas
Increased melanoma/squamous cell carcinoma in pale skin

90
Q

Explain the basic structure of hoof

A

Keratinised epidermis
Arranged as wall (unguis) and sole (subunguis)
Attached to bone by a highly-folded dermis (Corium)

91
Q

What is the basic structure of scales in birds?

A

Overlapping plates of heavily keratinsed epidermis

92
Q

What is the basic structure of fish skin?

A

Overlapping boney plates derived from dermis
Covered in epidermis

93
Q

What are the functions of skin?

A

Protective barrier
Chemical barrier
Normal flora - inhibits infectious agents
Temp regulation
Excretory organ
Sensory organ
Photoprotection
Immunosurveillance
Blood pressure regulation
Produces Vit D
Store nutrients (fat, water, vitamins)
Absorptive surface

94
Q

How does the skin regulate BP?

A

the body stores Na+ in the skin

95
Q

How does skin act as a secretory organ?

A

Sweat
Small amounts of urea, uric acid, ammonia and lactic acid

96
Q

Give examples of primary nutritional diseases that affect the skin

A

Proteins - poor hair growth, increased infection rates
Fatty acids - stark hair growth, greasy or dry skin and hair
Vits and mins

97
Q

Give examples of secondary nutritional diseases that affect the skin (change the way energy is available for the skin)

A

Hepatic dysfunction - reduced AA supply, necrosis of the skin
Pancreatic dysfunction - poor fat absorption, dry scurfy skin and pruritus
Bowel disease - poor absorption
Genetic inability to absorb minerals

98
Q

Explain the endocrine influences on the skin

A

Melanocyte stimulating hormone (MSH) stimulates melanocytes
Melatonin - infleunces moulting and hair growth

99
Q

Explain the hormonal influences of hair growth

A

Thyroid hormone and growth hormone stimulate hair growth
Adrenal cortical hormones and oestrogen decrease hair growth

100
Q

Explain the clinical signs of atrophic dermatosis

A

Reduced hair growth - alopecia eventually
Comedone formation due to blocked follicular openings

101
Q

In what diseases is atrophic dermatosis most common

A

Common in systemic endocrine disease
e.g., Hyperadrenocorticism (increased cortisol), hypothyroidism (decreased thyroid hormone) and sertoli cell tumour (increased oestrogen)

102
Q

What does atrophic dermatosis look like histologically?

A

thin epidermis and dermis
increased dermal ground substance
reduction in hair follicles, sebaceous and sweat glands
telogenic hair
little inflammation

103
Q

Explain the process of chronic dermatitis

A

Inflammatory mediators induce skin thickening and hyperpigmentation (blackening)
Increased blood supply
Increased numbers of inflammatory cells seen in the dermis
inflammatory cells crossing the epidermis with secondary infection

104
Q
A
105
Q

Describe the flea lifecycle

A
106
Q

Describe tabanidae lifecycle

A

Jorge ENI (81 decks)

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