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BRS Dermatology > Dermatology Pt 1 > Flashcards

Dermatology Pt 1 Flashcards

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Dermatology Board Prep flashcards
1
Q

The skin arises from the juxtaposition of 2 major embryological elements. Name them and their origin.

A

Epidermis - Originates from the ectoderm

Dermis - Arises from the mesoderm that comes into contact with inner surface of epidermis

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2
Q

What is the mesoderm essential for?

A

Mesoderm is essential for inducing differentiation of epidermal structures (e.g. Hair follicles.

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3
Q

Outline the stages of skin development (include weeks as well).

A
  1. Epidermis forms by week 4-single basal layer of cuboidal cells - Superior mesoderm layer.
  2. Secondary layer of squamous, non-keratinising cuboidal cells (periderm) develops in week 5 - generates white, waxy protective substance - vernix caseosa.
  3. From week 11, basal layer of cuboidal cells (stratum germinativum) proliferates to form multi-layered intermediate zone → 4 more superficial strata: spinosum (spinous), granulosum (granular), lucidum (clear) and corneum (horny).
  4. Epidermal ridges protrude as troughs into developing dermis beneath neurovascular supply develops into dermal papillae.
  5. Weeks 9-13: Development of hair follicles in stratum germinativum, and appearance of lanugo hair.
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4
Q

List the layers of superficial strata of the epidermis from deep to superficial.

A

Stratum germinativum (basal layer) → Stratum spinosum → Stratum granulosum → Stratum lucidum (found on palms of hands and soles of feet) → Stratum corneum

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5
Q

Where is the stratum lucidum found?

A

Found on palms of hands and soles only.

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6
Q

What are melanocytes derived from?

A

Neural crest → Melanoblasts

(Migrate dorsally between week 6-8 to developing epidermis, dermis and hair follicles).

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7
Q

By what week have most melanoblasts reached their destination and differentiated into melanocytes?

A

Weeks 12-13

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8
Q

What are melanocytes responsible for?

A

Melanocytes are responsible for melanin secretion, through melanogenesis.

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9
Q

What do a subset of melanoblasts form and why?

A

Melanocyte stem cells in hair follicle bulge to replenish differentiated melanocytes.

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10
Q

What regulates quantity and quality of melanocytes produced and explain how it is controlled?

A

Melanocortin 1 receptor (MC1R) → G protein-coupled receptor; Regulates quantity and quality of melanins produced by:

Agonists alpha-melanocyte-stimulating hormone (alpha-MSH) and ACTH mediate melanogenesis via MC1R. Binding of alpha-MSH to receptor ^ melanogenic cascade (tyrosine activity), and eumelanin production. ACTH can also up-regulate expression of MC1R gene.

alpha-MSH + ACTH → MC1R activation → melanogenic cascade → synthesis of eumelanin

Antagonist → Agouti signalling protein (ASP) → reverses effect of agonists and elicits production of pheomelanin.

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11
Q

What does ACTH up-regulate the effect of?

A

MC1R gene

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12
Q

Explain the regulation of melanocytes in accordance with UV-light.

A

Keratinocyte receives increased exposure to UV radiation, DNA damage induces mutation.

Increased expression of transcription factor MITF, and downstream melanogenic proteins (Pmel17, MART-I, TYR, TRPI and DCT) → Increases in melanin content.

Increased expression of PAR-2 in keratinocytes → increases uptake and distribution of melanosomes by keratinocytes.

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13
Q

What TF is increased due to UV-light and which downstream melanogenic proteins increase melanin content?

A

MITF

Pmel-17, MART-1, TYR, TRP1 and DCT

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14
Q

What does UV light cause keratinocytes to express?

A

PAR-2

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15
Q

What type of cells is the epidermis composed of?

A

Composed of keratinised, stratified squamous epithelium, avascular structure.

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16
Q

What is the dermis?

A

Layer of connective tissue and subcutaneous fat, deep to epidermis and separated by BM.

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17
Q

What is the epidermis composed of?

A

Keratinocytes

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18
Q

How long does cellular progression from basal layer to surface take?

A

~30 days (accelerated in skin diseases e.g. psoriasis)

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19
Q

What does the filamentous cytoskeleton of keratinocytes (in epidermis) contain?

A

(Thin) actin-containing microfilaments (7nm)

(Thick) tubulin-containing tubules (20-25nm)

Intermediate filaments (keratin) (7-10nm)

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20
Q

What are the roles of keratins?

A 
Cellular signalling 
Stress response 
Structural properties 
Apoptosis 
Wound healing
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21
Q

What are desmosomes and what are they made of?

A

Major adhesion complex in epidermis. Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes. Allow cells to withstand trauma.

Made up of desmoglein, desmocollin, plakoglobin, desmoplakin, keratin.

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22
Q

What other junctions are found in the epidermis and what are their functions?

A

Gap junctions - Clusters of intercellular channels (connexons), which directly form connections between cytoplasm of adjacent keratinocytes. Essential for cell synchronisation, differentiation, growth and metabolic coordination.

Adherens - Transmembrane structures which engage with the actin skeleton.

Tight junctions - Role in barrier integrity and cell polarity.

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23
Q

List the cells of the epidermis (not including keratinocytes).

A

Melanocytes - Dendritic, distribute melanin pigment (melanosomes) to keratinocytes.

Langerhans cells - Dendritic, APCs

Merkel Cells - Mechanosensory receptors

Mast cells

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24
Q

Are the number of melanocytes in people different?

A

No; number of melanocytes is the same among skin types (eumelanin causes darker skin)

25
Q

What is considered to be the dermal-epidermal junction, what does this structure consist of and what are its roles/functions?

A

Basement membrane

Consists of GPs, proteoglycans, collagen IV, VII, laminin and integrin.
Roles in cell adhesion and migration.

26
Q

Outline the structure of the dermis.

A

Dermis consists of 2 layers of connective tissue that compose of interconnected mesh of elastin and collagenous fibres produced by fibroblasts. Provides resilience.

Papillary layer - superficial, loose connective tissue, vascular

Reticular dermis - deep, dense, forms bulk of dermis

27
Q

What proteins are found in the dermis?

A 
Collagen (type I and III) - 80-85% of dermis. 
Elastic fibres (2-4%) - fibrillin + elastin 
GPs - Fibronectin, fibulin, integrins - facilitates cell adhesion and motility. 
Ground substance - Dermal collagen and elastic tissue (Glycosaminoglycan/ proteoglycan)
28
Q

What is the main cell present in the dermis and also what are the other cells present?

A

Fibroblasts

Histiocytes, mast cells, neutrophils, lymphocytes and dermal dendritic cells.

29
Q

What is the vascular supply of the skin?

A

Deep and superficial vascular plexus, doesn’t cross into epidermis.

30
Q

Outline the innervation of skin.

A

Sensory - Free, hair follicles, expanded tips

Autonomic - Cholinergic for eccrine; adrenergic for eccrine and apocrine

(1 million afferent nerves)

31
Q

What does one pilosebaceous unit consist of?

A

Hair, hair follicle, arrector pili muscle and sebaceous gland.

32
Q

What are the 2 types of afferent nerve endings from the skin? Give where they’re found, describe their receptors and examples of each.

A

Corpuscular - Dermis, encapsulated receptos e.g. Pacinian and meissners.

Free - Epidermis, non-encapsulated receptors e.g. Merkel cell

33
Q

What are Meissner’s corpuscles?

A

Encapsulated un-myelinated mechanoreceptors that responds to light touch (+ slow vibration). Senses low-frequency stimulation at level of dermal papilla.

34
Q

Where are Meissner’s corpuscles most concentrated?

A

Thick, hairless skin (finger pads and lips)

35
Q

What are Ruffini corpuscles?

A

Slow acting mechanoreceptors, sensitive to skin stretch, deep in dermis, spindle-shaped, high density around fingernails and monitors slippage.

aka - Bulbous corpuscles

36
Q

Where are Ruffini’s corpuscles most concentrated?

A

High density around fingernails

37
Q

What are Pacinian corpuscles?

A

Encapsulated, phasic (rapidly adapting) mechanoreceptor, deep pressure and vibration; vibrational role (detects surface texture); Predominantly found in dermal papillae of hands and feet.

aka - Lamellar corpuscles

38
Q

What are Merkel cells?

A

Non-encapsulated mechanoreceptors, detecting light/sustained touch, pressure.
Oval shaped. Modified epidermal cells.

39
Q

Where are Merkel cells found?

A

Stratum basale, directly above BM.
Palms, soles, oral and genital mucosa.
Mainly in fingertips.

40
Q

Which nerve endings detect light touch?

A

Meissner, Merkel, free

41
Q

Which nerve endings detect touch, pressure?

A

Merkel, Ruffini, Pacinian, Free

42
Q

Which nerve endings detect vibration?

A

Meissner and Pacinian

43
Q

Which nerve endings detect temperature?

A

Thermoreceptor

44
Q

Which nerve endings detect pain?

A

Nociceptor (free nerve endings)

45
Q

What bacteria predominates in the microbiome of the skin?

A

Predominantly Actinobacteria (including Propionibacteria and Corynebacteria), Firmicutes (Clostridia and Bacili [Staph], Bacteriodetes and Proteobacteria.)

46
Q

What are the nerve fibres of light touch, pressure/touch, vibration, temperature and pain?

A 
Light touch - A-beta 
Vibration - A-beta 
Pressure, touch - A-beta and A-delta 
Temperature - A-delta and C 
Pain - A-delta and C
47
Q

How does the innervation of skin vary for different body sites?

A

Face, extremities and genitalia have richer innervation than rest body.

48
Q

What are the functions of the skin?

A 
Sensation 
Physical barrier 
Aesthetic appearance
Thermoregulation 
Immunological barrier 
Metabolism
49
Q

What are Langerhans Cells?

A

Dendritic APCs, residing within the basal layer within the epidermis. Initiates immune response and also contributes to immune tolerance.

50
Q

What are the functions of Langerhans Cells?

A

Dendritic processes extends through intercellular tight junctions to sample the stratum corneum.
Interpret microenvironmental context → Determines appropriate quality of immune response.
In absence of danger, promote expansion and activation of skin-resident regulatory cells (Tregs).
Detection of PAMPs → rapid initiation of innate antimicrobial responses.
Induction of adaptive immune response: Power and specific of T-cell.

51
Q

Which cells in the dermis carry out immune surveillance?

A

Tissue-resident T-cells

Macrophages

DCs

52
Q

Outline the immune barrier of the skin.

A

Keratinocyte-derived endogenous antimicrobial peptides are secreted (Defensins, cathelicidins). Expression of cathelicidin is enhanced by keratinocyte activity, predominantly residing within granules of the superficial epidermis → Innate immune defence.

53
Q

Explain the what the physical barrier formed by the skin is.

A

Cornified cell envelope and stratum corneum restrict water and protein loss from the epidermis. (High output cardiac failure and renal failure in extensive disease.)

54
Q

What has an important role in cushioning trauma?

A

Subcutaneous fat

55
Q

What protects us against UV-induced damage?

A

Melanin in basal keratinocytes.

56
Q

Outline the role of skin in thermoregulation.

A

Thermoregulatory centre of the hypothalamus detects temperature of blood.

Increase in blood temperature is identified by central receptors; the sympathetic NS is continuously monitoring the body temperature, and initiating appropriate motor responses.

Warm environment - Vasodilation occurs. More blood flows through capillaries, dilating them with the pressure; less blood flows through deeper shunt vessels. More blood flow close to surface - temperature gradient become steeper; cooling by conduction and radiation increased.

Eccrine sweat glands - cooling effect.

57
Q

List the metabolic functions of the skin.

A

Vitamin D synthesis

Subcutaneous fat:
Storage via lipogenesis, glucose is converted into triglycerides stored within adipocytes. CALORIE RESERVE
Hormonal - Leptin acts on hypothalamus to regulate hunger and energy metabolism

58
Q

What hormone acts on hypothalamus to regulate hunger and energy metabolism?

A

Leptin

59
Q

List some skin diseases that can affect psychosexual function and can increase the risk of suicide.

A

Vitiligo
Acne
SLE
Hydradenitis superativa (malodorous inflammatory nodules)

BRS Dermatology (2 decks)

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