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
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
3
Q
What does periderm generate?
A
- white, waxy protective substance - vernix caseosa
- protects foetus from amniotic fluid and also from bacteria after birth
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)
5
Q
What is a basic overview of the structure of the skin?
A
- epidermis
- basement membrane (dermal-epidermal junction)
- dermis
- subcutaneous fat
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
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)
8
Q
What are the roles of keratins?
A
- structural properties
- cell signalling
- stress response
- apoptosis
- wound healing
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
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
11
Q
What are adherens junctions? (junctions that connect keratinocytes)
A
- transmembrane structures
- engage with the actin cytoskeleton
12
Q
What are tight junctions? (junctions that connect keratinocytes)
A
- role in barrier integrity and cell polarity
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)
14
Q
What are Langerhans cells? (other cells in epidermis)
A
- dendritic
- antigen-presenting cells
15
Q
What are Merkel cells? (other cells in epidermis)
A
- mechanosensory receptors
- mast cells are also present in the epidermis
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
What are Ruffini corpuscles (aka bulbous corpuscles)?
- slow acting mechanoreceptors deeper in dermis
- spindle-shaped, encapsulated
- highest density around fingernails
- sensitive to skin stretch
- monitor slippage of objects
26
What are Pacinian corpuscles (aka lamellar corpuscles)?
- 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
What are Merkel cells?
- 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
Summary of skin innervation
- light touch - Meissner, Merkel, Free
- touch and pressure - Merkel, Ruffini, Pacinian, Free
- vibration - Meissner, Pacinian
- temperature - thermoreceptor
- pain - nociceptor (free nerve endings)
29
What is the skin microbiome?
- microbiota - bacteria, fungi and viruses
- microbiome - genome of microbiota
- predominantly actinobacteria, firmicutes, bacteroidetes and proteobacteria
30
What are the functions of the skin?
- immunological barrier
- physical barrier
- thermoregulation
- sensation
- metabolism
- aesthetic appearance
31
How does skin act as an immunological barrier?
- 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
What do Langerhans cells do?
- 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
How does skin act as a physical barrier?
- 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
How is skin involved in thermoregulation?
- vasodilation or vasoconstriction in deep/superficial vascular plexuses regulate heat loss
- eccrine sweat glands give an evaporative cooling effect
- role in fluid balance
35
How is skin involved in metabolism?
- 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
How is skin involved in aesthetic appearance?
- psychosexual function
- increased risk of suicide with people with skin condition
