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Dermatology > Structure and function of the skin > Flashcards

Structure and function of the skin Flashcards

1
Q

What are the 3 main layers of the skin?

A

Epidermis
Dermis
Sub-cutis

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2
Q

What is the epidermis?

A

This is the outer layer of the skin and is made up of stratified squamous epithelium

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3
Q

What cells make up the epidermis?

A

Keratinocytes (95%)
Melanocytes
Langerhan’s cells
Merkel cells

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4
Q

What are the 4 main layers of the epidermis?

A

Keratin layer - Stratum corneum
Granular layer - Stratum granulosum
Prickle cell layer - Stratum spinosum
Basal layer - Stratum basale

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5
Q

What layer of the epidermis is found only in the palms and soles?

A

Clear layer - Stratum lucidum

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6
Q

Describe the structure of the keratin layer?

A

The keratin layer is made up of corneocytes, which are overlapping, non-nucleated cell remnants, which form the insoluble cornified envelope

This layer contains 80% keratin and filaggrin

Lamellar granules release lipids, forming a tight waterproof barrier

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7
Q

What is the function of the stratum lucidum in the hands and soles?

A

To reduce friction between the keratin and granular layer

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8
Q

Describe the structure of the granular layer of the epidermis

A

It is made up of 2-3 layers of flatter cells, containing large keratohyalin granules, which store structural filaggrin and involucrin proteins

These cells also contain Odland (Lamellar) bodies, which are secretory organelles that contribute to the skin barrier

They have a high lipid contain with a lost cell nucleus

They are the origin of the cornified envelope

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9
Q

Describe the structure of the prickle cell layer of the epidermis

A

It is made up of large, polyhedral cells and contains many desmosomes

Intermediate filaments connect to the desmosomes

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10
Q

Describe the structure of the basal layer of the epidermis

A

It is comprised of small cuboidal cells with lots of intermediate keratin filaments

It is usually 1 cell thick

It is highly metabolically active

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11
Q

Describe the structure of the basement membrane

A

The epidermal basement membrane is made up of laminin and collagen IV

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12
Q

What are some factors that regulate epidermal turnover?

A

Growth factors
Cell death
Hormones

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13
Q

What are melanocytes?

A

Melanocytes are pigment producing dendritic cells

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14
Q

Where are melanocytes found?

A

In the basal layer and above

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15
Q

How do melanocytes cause skin pigmentation?

A

Melanocytes contain organelles known as melanosomes, which convert tyrosine to melanin pigment

Melanin absorbs light and acts as a neutral density filter

Full melanosomes, called melanin granules, are transferred to adjacent keratinocytes via dendrites to form a protective cap over the nucleus in basal cells

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16
Q

What are the 2 main types of melanin pigment?

A
  • Eumelanin - Brown or black
  • Phaeomelanin - Red or yellow
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17
Q

What is a tumour of melanocytes called?

A

Melanoma

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18
Q

What determines skin colour?

A

Amount of melanin (Size of melanosomes) Number of keratin layers
Eumelanin and phaeomelanin levels

NOTE: The number of melanocytes stays the same!!

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19
Q

What causes darker coloured skin?

A

More cells in the keratin layer
Larger melanosomes in the keratin layer
More eumelanin
Movement of melanosomes from the basal layer

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20
Q

What causes lighter skin?

A

Fewer cells in the keratin layer
Smaller melanosomes in the keratin layer
More phaeomelanin
Melanosomes restricted to basal layer

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21
Q

What is vitiligo?

A

An autoimmune condition in which there is a loss of melanocytes, leading to skin depigmentation

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22
Q

Where do Langerhan’s cells form?

A

They are mesenchymal in origin, forming in the bone marrow

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23
Q

Where are Langerhan’s cells found?

A

In the prickle cell level of the epidermis, and also in the dermis and lymph nodes

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24
Q

What is the function of Langerhan’s cells?

A

They are involved in the skin immune system, functioning as APCs, picking up an antigen in the skin and circulating to the lymph nodes via the lymphatic system

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25
What is an example of a condition affecting the Langerhan's cells of the skin?
Langerhan's cell histiocytosis
26
What is the unique organelle found in Langerhan's cells?
Racquet organelles (Birbeck granules)
27
What is the function of racquet organelles in the Langerhan's cells?
They are thought to be involved in the trafficking of antigens
28
Name the organelle
Racquet organelle (Birbeck granules)
29
What are Merkel cells?
These are mechanoreceptor cells found in the basal layer, between the keratinocytes and nerve fibres
30
What are some examples of mucosal membranes?
- Eyes (Ocular mucosa) - Mouth (Oral mucosa) - Nose - Genito-urinary - GI tract
31
What are some of the regions of the oral mucosa?
Masticatory mucosa Lining mucosa Tongue papillae
32
How is the masticatory mucosa adapted for function?
It is keratinised to deal with friction and pressure of mastication
33
What are some structures present in the ocular mucosa?
Lacrimal glands Eye lashes Sebaceous glands
34
What is the name of the junction between the epidermis and dermis?
Dermo-epidermal junction
35
What are some of the functions of the dermo-epidermal junction?
- Support, anchorage, adhesion, growth and differentiation of basal cells - Semi-permeable membrane acting as barrier and filter
36
What is the name of the junctions between the cells of the epidermis and the extracellular matrix, holding the epidermis to the dermis?
Hemidesmosomes
37
What is the name of the junctions connecting the epidermal cells together at the dermo-epidermal junction?
Desmosomes
38
What are some conditions that affect the demo-epidermal junction?
- Bullous pemphigoid - Epidermolysis bullosa (Genetic defect affecting molecules involved in skin adhesion)
39
What are some structures that make up the dermis? (9)
- Ground substance - Cells (fibroblasts, macrophages, mast cells, lymphocytes, Langerhans cells) - Collagen (Type I and III) - Elastin - Blood vessels - Lymphatics - Nerves - Muscles - Ground substances (Hyaluronic acid + Chondroitin suphate)
40
What is the function of fibroblasts in the dermis?
Fibroblasts maintain ground substance by producing collagen
41
What are the 2 main regions of the dermis?
- Papillary dermis - Thin, just beneath depidermis - Reticular dermis - Thick, bundles of type 1 collagen, containing the appendages
42
How does the dermis of the skin differ in different ethnic backgrounds?
Asian, Hispanic/ Latino and African/ American skin types have a thicker dermis (proportional to degree of pigmentation) than caucasian skin types and smaller collagen fibres African/ American skin has larger and more numerous fibroblasts
43
What structure allows the bypassing of superficial capillaries in cold weather?
AV shunts (Anastomoses)
44
How are lymphatic vessels arranged in the skin?
Lymphatic vessels in the skin are arranged into sub-epidermal meshed networks Smaller non-contractile vessels feed into larger contractile lymphatic trunks, allowing for the continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
45
What are the functions of the lymphatic vessels in the skin?
These lymphatic vessels have important immune functions, such as allowing the passage of Langerhans cells to lymph nodes and the channelling of micro-organisms / toxins towards the lymph nodes
46
What is a condition affecting the lymphatic vessels of the skin?
Lymphoedema
47
What types of nerves are present in the skin?
Somatic sensory nerves Motor nerves Autonomic nerves
48
What structures provide signals to somatic sensory nerves in the skin?
Free nerve endings Special receptors
49
What are some examples of special receptors found in the skin?
Pacinian corpuscles (Pressure sensors) Meissner's corpuscles (Vibration sensors)
50
What structures in the skin are supplied by the autonomic nervous system?
Blood vessels Nerves Glands
51
What are the 3 main types of glands in the skin?
- Sebaceous glands - Apocrine glands - Eccrine glands
52
What type of gland is shown?
Sebaceous gland
53
Where are sebaceous glands most concentrated in the body?
Face Chest Back
54
What is the function of sebaceous glands?
They perform holocrine secretion of sebum into the opening of pilary canal (Hair canal)
55
What makes up sebum?
- Squalene - Wax esters - TG - FFA
56
What stimulates sebaceous gland activity?
Hormones (Androgens), they are quiescent pre-puberty
57
What is the function of sebum?
Sebum helps to control moisture loss and protect against fungal infection
58
What is a common pathology of the sebaceous glands?
Acne vulgaris
59
What type of gland is shown?
Apocrine sweat gland
60
Where are apocrine sweat glands most commonly found?
Axillae, groin, eyelids, ears, mammary and perineal regions
61
Where in the skin do apocrine glands travel?
From the dermis of the skin into the pilosebaceous unit (Hair follicle)
62
What stimulates apocrine sweat glands?
Androgens
63
What is the function of apocrine sweat glands?
They secrete an oily fluid, the function of which is unknown
64
What causes body odour?
Bacterial decomposition of the oily fluid produced by apocrine sweat glands
65
What is a condition affecting the apocrine sweat glands?
Hidradenitis suppuritiva - Apocrine inflammation
66
What gland is shown?
Eccrine sweat glands
67
What simulates eccrine sweat glands?
Sympathetic, cholinergic nerve supply
68
What are some stimuli to eccrine gland action?
Mental stimulation Thermal stimulation Gustatory stimulation
69
Where are eccrine glands found?
They cover the whole skin surface
70
What is the function of eccrine sweat glands?
Eccrine sweat glands play a role in ultrafiltration of the body’s fluids and contribute around the same amount as 1 kidney They function in cooling by evaporation and moistening of palms and soles to aid grip
71
What is a condition affecting the eccrine sweat glands?
Miliaria (Sweat rash) - Heat induced blockage of the eccrine glands
72
What are the components of the pilosebaceous unit?
Hair follicle Hair shaft Arrector pili muscle Sebaceous glands
73
What are the 3 main segments of the hair follicle?
Infundibulum Isthmus Hair bulb
74
What causes hair pigmentation?
Melanocytes producing melanin pigment: More melanin means darker hair
75
Where does hair pigmentation by melanocytes occur?
Above the dermal papilla
76
Describe the features of hairs in those of Asian descent
Straight, round, large cross-sectional area, fastest growth rate; strong and durable
77
Describe the features of hair in those of African descent
Lowest hair density, curly/ spiral (ellipsoidal cross section), slowest growth rate; most fragile
78
Describe the features of hair in those of Caucasian descent
Straight to curly; round/ oval cross section; highest hair density, most moisture content; comparable strength with Asian hair
79
What are the 3 main types of hair?
Lanugo hair Vellus Terminal
80
What is lanugo hair?
Fine long hairs covering the foetus (Shed about 1 month before birth)
81
What is vellus hair?
Fine, short hair covering much of the body surface (Replaces lanugo hairs before birth)
82
What is terminal hair?
Long, coarse hairs (E.g. scalp and pubic area), the growth of which is influenced by androgen levels
83
What are the 3 phases of hair growth?
Anagen - Growing Catalan - Involuting Telogen - Resting
84
How does hair stability change in pregnant women?
In pregnancy, increase in hormone levels causes increased hair stability, however, around 2 weeks post partum, hair stability and hair growth in anagen phase will plummet
85
What are the patterns of male pattern hair loss?
Typical Vertex Anterior
86
What is the name of the folds at the edges of the nails?
Lateral nail folds
87
What is the name of the white semicircle at the bottom of the nail?
Lunula
88
What is the name of the skin flap that lays over the nail plate at the bottom?
Cuticle
89
What is the name of the fold of skin at the bottom of the nail?
Posterior nail fold
90
What is the name of the structure beneath the the end of the nail?
Hyponychium
91
What are the 3 layers of the nail plate?
Dorsal - Top Intermediate Ventral - Bottom
92
Describe the structures of the nail and nail bed
93
What are the functions of the skin? (6)
- Barrier function - Metabolism and detoxification - Thermoregulation - Immune defence - Communication - Sensory functions
94
What does the skin form a physical barrier against?
Friction Mechanical trauma UV radiation (Via melanin caps)
95
What does the skin provide a chemical barrier against?
Irritants Allergens Toxins
96
What are some conditions that affect the barrier function of the skin?
- Steroid-sulphatase deficiency X-linked ichthyosis - Cumulative irritant hand dermatitis - Ulcer
97
What are some of the metabolic functions of the skin?
- Vitamin D metabolism - Thyroid hormone metabolism - Defence against chemicals, drugs, pollutants and sunlight
98
Describe the skins function in vitamin D metabolism
Ultraviolet B radiation is responsible for conversion of 7-dehydrocholesterol into vitamin D3 (Cholecalciferol) in the skin Vitamin D3 is stored as hydrocycholecalciferol in the liver and is converted to 1,25-dihydroxycholecalciferol in the kidneys
99
How does the skin function in thyroid hormone metabolism?
The skin plays an important role in the conversion of thyroxine (T4), to Triiodothyronine (T3), which is biologically active
100
How does the skin detect temperature changes?
Thermoreceptors (E.g. Krause end bulbs cold, Ruffini ends warm)
101
What are some ways in which skin can react to temperature changes?
Behaviour control Sweating Shivering Av anastomoses in the skin changing blood flow
102
How does the skin provide immune defence?
Secretion of anti-microbial oils and the presence of Langerhan’s and T cells within the skin
103
What are some failures of skin immune defences?
- Crusted scabies - Tuberculoid leprosy (Hansen’s disease) - Granulomatous disease - Eczema herpeticum (Disseminated HSV infection) - Chronic discoid lupus erythematosus
104
How does the skin play a role in communication?
Through visual changes, odour and sociosexual behaviour
105
What is meant by stigma?
The situation of an individual who is disqualified from full social acceptance
106
What are some of the sensory functions of the skin?
- Touch - Pressure - Vibration - Pain - Itch - Hot/Cold
107
What are some of the consequences of barrier function failure?
- Fluid loss → Dehydration - Protein loss → Hypoalbuminaemia - Infection
108
What is a consequence of thermoregulatory failure of the skin?
Heat loss -> Hypothermia
109
How can skin diversity present
- Differences in how the same disease presents in different people - Different diseases more likely in certain peoples - Variation between severity in diseases between people - Differences in presentations caused by practises of specific cultures (e.g. cupping)
110
What are some skin differences that can affect how skin diseases affect someone?
- Skin colour - Density of keratin layer - Function of the dermo-epidermal junction - Susceptibility to irritants
111
What are some of the immune structures found in the skin?
- Kertin layer (Stratum corneum) - Stratification - Immune cells (Langerhans, T-cells, dendritic cells) - Keratinocytes - Cytokines, chemokines, eicosanoids - Antimicrobial peptides
112
How does the keratin layer form a barrier against pathogens?
It is a tough, lipid rich physical barrier against infection, formed by the terminal differentiation of keratinocytes to corneocytes They produce antimicrobial peptides (AMPs) that can directly kill pathogens and cytokines and chemokines, which recruit and regulate cells of the adaptive and innate immune system
113
What is the function of Langerhan's cells in the skin?
They act as sentinels in the epidermis and process lipid antigen and microbial fragments, before presenting them to effector T cells
114
From what lineage do Langerhan's cell arise?
From the macrophage lineage
115
What lymphocytes are mostly present in the epidermis?
CD8+ T-cells
116
What lymphocytes are found in the dermis?
CD4+ and CD8+ T-cells
117
What skin condition is associated with Th1 cells?
Psoriasis
118
What skin condition is associated with Th2 cells?
Atopic dermatitis
119
What skin conditions are associated with Th17 cells?
Psoriasis and atopic dermatitis
120
What are the functions of Th1 cells?
Activates macrophages to destroy microorganisms, secrete IL2 and IFN-gamma
121
What are the functions of Th2 cells?
Help B cells to make antibodies, secrete IL4, IL5, IL13
122
What are the functions of the Th17?
Modulate skin and mucosal immunity, secretes IL17
123
What is the main type of dendritic cell found in the dermis?
Plasmacytoid dendritic cells
124
What is the function of plasmacytoid dendritic cells?
They are the main source of alpha-interferon and transmit information to T and B cells They constantly rotate between the skin and the lymph nodes and will activate T and B cells once they present antigens
125

Dermatology (38 decks)

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