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Year 1 - BRS > 9.1 - Introduction to Dermatology Part 1 > Flashcards

9.1 - Introduction to Dermatology Part 1 Flashcards

1
Q

What are the main juxtaposing embryological layers of the skin?

A
  • epidermis - originates from ectoderm
  • dermis - originates from mesoderm that comes into contact with inner surface of epidermis
  • mesoderm essential for inducing differentiation of epidermal structures e.g. hair follicle
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2
Q

Describe the stages of development of epidermis and dermis

A
  • week 5 - epidermis forms as single basal layer of cuboidal cells
  • secondary layer of squamous, non-keratinising cuboidal cells (periderm) develops - cells with projecting globules covered with small protrusions (microvilli)
  • week 11 - basal layer of cuboidal cells (stratum germinativum aka stratum basale) proliferates to form multilayered intermediate zone
  • weeks 9-13 - development of hair follicles in stratum germinativum and appearance of lanugo hair
  • weeks 12-14 - epidermal ridges protrude as troughs into developing dermis beneath (rete ridge)
  • neurovascular supply develops into dermal papillae
  • week 20 - further proliferation and differentiation into four more superficial strata
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3
Q

What does periderm generate?

A
  • white, waxy protective substance - vernix caseosa
  • protects foetus from amniotic fluid and also from bacteria after birth
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4
Q

What are the names of the four strata differentiated from multilayered intermediate zone in week 20?

A

From deep to superficial:

  • stratum spinosum (spinous)
  • stratum granulosum (granular)
  • stratum lucidum (clear - found on palms of hands and soles of feet only)
  • stratum corneum (horned)
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5
Q

What is a basic overview of the structure of the skin?

A
  • epidermis
  • basement membrane (dermal-epidermal junction)
  • dermis
  • subcutaneous fat
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6
Q

What is the structure of the epidermis?

A
  • composed of keratinocytes (most abundant cell)
  • cells in basal layer are small and cuboidal and undergo progressive differentiation and flattening:
  • stratum spinosum
  • stratum granulosum (granules of keratohyalin)
  • stratum lucidum (only palms and soles, no nuclei or organelles)
  • stratum corneum (no nuclei or organelles)
  • cellular progression from basal layer to surface in 30 days - accelerated in skin diseases e.g. psoriasis
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7
Q

What is the structure of keratinocytes?

A
  • filamentous cytoskeleton comprising:
  • actin-containing microfilaments (7nm)
  • tubulin-containing microtubules (20-25nm)
  • intermediate filaments (keratins) (7-10nm)
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8
Q

What are the roles of keratins?

A
  • structural properties
  • cell signalling
  • stress response
  • apoptosis
  • wound healing
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9
Q

What are desmosomes? (junctions that connect keratinocytes)

A
  • major adhesion complex in epidermis
  • anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes
  • allow cells to withstand trauma
  • contain many protein components
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10
Q

What are gap junctions? (junctions that connect keratinocytes)

A
  • clusters of intercellular channels (connexons)
  • directly form connections between cytoplasm of adjacent keratinocytes
  • essential for cell synchronisation, cell differentiation, cell growth and metabolic coordination
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11
Q

What are adherens junctions? (junctions that connect keratinocytes)

A
  • transmembrane structures
  • engage with the actin cytoskeleton
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12
Q

What are tight junctions? (junctions that connect keratinocytes)

A
  • role in barrier integrity and cell polarity
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13
Q

What are melanocytes? (other cells in epidermis)

A
  • dendritic
  • distribute melanin pigment (in melanosomes) to keratinocytes
  • number of melanocytes equal among skin types (just amount of melanin made varies)
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14
Q

What are Langerhans cells? (other cells in epidermis)

A
  • dendritic
  • antigen-presenting cells
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15
Q

What are Merkel cells? (other cells in epidermis)

A
  • mechanosensory receptors
  • mast cells are also present in the epidermis
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16
Q

What is the structure and function of the basement membrane/dermal-epidermal junction?

A
  • made up of proteins and glycoproteins like collagens (IV, VII), laminin, integrins
  • roles include:
  • cell adhesion
  • gate-keeping functions - cell migration, diffusion of bioactive molecules
  • rete ridges - strength, niche for epidermal stem cells
  • roles in development, morphogenesis, wound healing and skin remodelling
17
Q

What are the two layers of the dermis?

A
  • papillary dermis - superficial, loose connective tissue, vascular
  • reticular dermis - deep, dense connective tissue, forms bulk of dermis
18
Q

What substances make up the dermis?

A
  • proteins - 80-85% collagen (mainly types I and III), 2-4% elastic fibres (fibrillin, elastin)
  • glycoproteins - fibronectin, fibulin, integrins - facilitate cell adhesion and motility
  • ground substance - between dermal collagen and elastic tissue - glycosaminoglycans and proteoglycans - maintain hydration of dermis due to high water binding capacity of hyaluronic acid
19
Q

What are the cells in the dermis?

A
  • fibroblasts - primary cells within dermis
  • histiocytes
  • mast cells
  • neutrophils
  • lymphocytes
  • dermal dendritic cells
20
Q

What is the blood supply to the skin like?

A
  • deep and superficial vascular plexus
  • does not cross into epidermis
  • pilosebaceous unit
  • arrector pili muscle / arterioles / shunts
21
Q

What is innervation to the skin like?

A
  • sensory - free nerve endings, hair follicles and expanded tips
  • one million afferent nerve fibres that form branching network often accompanying blood vessels, to form a mesh of interlacing nerves in superficial dermis
  • distribution varies by body site e.g. face, extremities and genitalia are more richly innervated than rest of skin
22
Q

What is innervation to sweat glands like?

A
  • autonomic
  • cholinergic innervation to eccrine sweat glands (salty water non-smelling sweat)
  • adrenergic innervation to eccrine and apocrine (body odour sweat in armpits and genitals) sweat glands
23
Q

What two types of afferent nerve are there?

A
  • free-ended that end in non-encapsulated receptors in the epidermis e.g. Merkel cell
  • corpuscular that end in encapsulated receptors in the dermis e.g. Pacinian, Meissner’s
24
Q

What are Meissner’s corpuscles (aka tactile corpuscles)?

A
  • encapsulated, unmyelinated mechanoreceptors in dermal papilla
  • lamellated capsule
  • superficial dermis
  • most concentrated in thick hairless skin (finger pads and lips)
  • detect light touch and slow vibration - low frequency stimulation
25
Q

What are Ruffini corpuscles (aka bulbous corpuscles)?

A
  • slow acting mechanoreceptors deeper in dermis
  • spindle-shaped, encapsulated
  • highest density around fingernails
  • sensitive to skin stretch
  • monitor slippage of objects
26
Q

What are Pacinian corpuscles (aka lamellar corpuscles)?

A
  • encapsulated, ovoid
  • rapidly adapting (phasic) mechanoreceptor
  • detects deep pressure and vibration (deep touch)
  • also detects surface texture - vibrational role
  • dermal papillae of hands and feet
27
Q

What are Merkel cells?

A
  • non-encapsulated mechanoreceptors
  • detect light/sustained touch and pressure
  • oval-shaped
  • modified epidermal cells
  • found in stratum basale
  • most populous in fingertips, also found in palms, soles, oral and genital mucosa
28
Q

Summary of skin innervation

A
  • light touch - Meissner, Merkel, Free
  • touch and pressure - Merkel, Ruffini, Pacinian, Free
  • vibration - Meissner, Pacinian
  • temperature - thermoreceptor
  • pain - nociceptor (free nerve endings)
29
Q

What is the skin microbiome?

A
  • microbiota - bacteria, fungi and viruses
  • microbiome - genome of microbiota
  • predominantly actinobacteria, firmicutes, bacteroidetes and proteobacteria
30
Q

What are the functions of the skin?

A
  • immunological barrier
  • physical barrier
  • thermoregulation
  • sensation
  • metabolism
  • aesthetic appearance
31
Q

How does skin act as an immunological barrier?

A
  • Langerhans cells
  • tissue-resident T cells, macrophages and dendritic cells carry out immune surveillance in dermis to give rapid, effective immunological backup if epidermis is breached
  • keratinocytes make their own endogenous antibiotics (defensins and cathelicidins) - part of innate immune defence against bacteria, viruses and fungi
32
Q

What do Langerhans cells do?

A
  • dendritic cell / macrophage family, both innate and adaptive immunity
  • sentinel cells in epidermis
  • initiate immune response against microbial threats
  • also contribute to immune tolerance
  • form dense network with which potential invaders must interact
  • specialised at ‘sensing’ environment
  • extend dendritic processes through intercellular tight junctions to sample outermost layers of skin (stratum corneum)
  • interpret microenvironmental context = determine appropriate quality of immune response
  • absence of danger - promote expansion and activation of skin-resident regulatory cells (Tregs)
  • when toll-like receptors sense danger via PAMPs –> rapid initiation of innate antimicrobial responses
  • induction of adaptive response - power and specificity of T cell/B cell and antibodies
33
Q

How does skin act as a physical barrier?

A
  • physical barrier against external environment
  • cornified cell envelope and stratum corneum restrict water and protein loss from skin
  • subcutaneous fat - important role in cushioning trauma
  • UV barrier
  • melanin in basal keratinocytes - protection against UV-induced DNA damage
34
Q

How is skin involved in thermoregulation?

A
  • vasodilation or vasoconstriction in deep/superficial vascular plexuses regulate heat loss
  • eccrine sweat glands give an evaporative cooling effect
  • role in fluid balance
35
Q

How is skin involved in metabolism?

A
  • vitamin D synthesis - conversion of 7-dehydrocholesterol into cholecalciferol
  • subcutaneous fat has calorie reserves - 80% of total body fat in non-obese people is subcutaneous
  • hormone (leptin) release - acts on hypothalamus - regulates hunger and energy metabolism
36
Q

How is skin involved in aesthetic appearance?

A
  • psychosexual function
  • increased risk of suicide with people with skin condition

Year 1 - BRS (73 decks)

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