Dermatology Flashcards
4 major layers of skin
Epidermis
Basement membrane (dermal-epidermal junction)
Dermis
Subcutaneous fat
What kind of cells compose the epidermis
Keratinocytes
What are the 5 layers of the epidermis?
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum(Only on palms+soles)
Stratum corneum
Describe cellular progression in the epidermis
Cellular progression from basal layer → surface in ~30 days
Accelerated in skin diseases (e.g. psoriasis)
What are the 3 ‘other’ cells in the epidermis and what are their functions?
Melanocytes
Dendritic
Distribute melanin pigment (in melanosomes) to keratinocytes
Number of melanocytes = among skin types.
Langerhans cells
Dendritic
Antigen‐presenting cells
Merkel cells
Mechanosensory receptors
What are the kinds of junctions between cells in the epidermis and what are they useful for?
-Gap junctions
Essential for cell synchronization, cell differentiation, cell growth and metabolic coordination
-Adherens junctions
-Desmosomes
Major adhesion complex in epidermis
Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes,
Allow cells to withstand trauma.
-Tight junctions
Role in barrier integrity and cell polarity
Melanocyte
Merkel cell
Langerhans cell
2 layers of the dermis and what does the ECM provide?
Papillary dermis
Reticular dermis
Supporting (extracellular) matrix– provides resilience
What are the cells present in the dermis?
Fibroblasts: primary cells within dermis
Also present:
Histiocytes
Mast cells
Neutrophils
Lymphocytes
Dermal dendritic cells
What are the major molecules that make up the dermis and what are their properties
Proteins
Collagen (80-85% of dermis) – mainly types I and III
Elastic fibres (2-4%) – fibrillin, elastin
Glycoproteins – fibronectin, fibulin, intregrins
– facilitate cell adhesion and cell motility
Ground substance – between dermal collagen and elastic tissue – glycosaminoglycan / proteoglycan
C
Is the epidermis vascular?
No, avascular
Describe the innervation of the skin
Sensory
Free, hair follicles, expanded tips
Autonomic
Eccrine: Cholinergic and andrenergic
Apocrine: Andrenergic only
Where are they most abundant and what is the function of meissners’ corpuscle?
Most concentrated in thick hairless skin, (finger pads and lips)
Light Touch (+slow vibration)
Where are they most abundant and what is the function of ruffinis’ corpuscle?
Highest density around fingernails
Sensitive to skin stretch
Monitors slippage of objects
What organisms form the majority of the skin microbiota?
Bacteria, viruses, fungi
(Predominantly Actinobacteria (including Propionibacteria and Corynebacteria), Firmicutes (Clostridia and Bacilli [Staphylococcus] , Bacteroidetes & Proteobacteria)
Is the merkel cell encapsulated and what is its function?
(unencapsulated)
Light / sustained touch, pressure
Where are they found and what is the function of the pacinian corpuscle?
Dermal papillae of hands and feet
Deep pressure and vibration (deep touch)
Vibrational role - detects surface texture
C
What is the role of the skin microbiota?
Role in immune-modulation and epithelial health
6 skin functions
Physical barrier
Immunological barrier
Thermoregulation
Sensation
Metabolism
Aesthetic appearance
How do langerhans cells regulate the adaptive immune response?
Specialized 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.
In absence of danger, promote expansion and activation of skin-resident regulatory - cells (Tregs)
When toll-like receptors (TLRs) sense danger (via pathogen associated molecular patterns [PAMP]) → rapid initiation of innate antimicrobial responses
Induction of adaptive response - power and specificity of T-cell / B-cell and antibodies (immunoglobulins)
How do toll-like receptors detect danger?
PAMPs(Pathogen associated molecular patterns)
What is the function of antimicrobial peptides?
Keratinocyte‐derived endogenous antibiotics (defensins and cathelicidins) → innate immune defence against bacteria, viruses and fungi
What are the differences between the innate and adaptive immune system?
What cells detect pathogens in the dermis and what does their activation lead to
Tissue‐resident T-cells
Macrophages
Dendritic cells
Rapid, effective immunological backup if epidermis breached
What layers of skin reduce water and protein loss?
Cornified cell envelope and stratum corneum restrict water and protein loss from skin
What in the skin protects from UV-DNA damage?
Melanin in basal keratinocytes - protection against UV-induced DNA damage
What layer of the skin reduces trauma?
Subcutaneous fat
How does extensive skin damage affect our cardiac and renal function?
high-output cardiac & renal failure in extensive skin disease
How does the body regulate temperature in increased temperature?
Apart from regulating temperature, what other function does the eccrine system regulate in the body?
Role in fluid balance
What are the metabolic functions of the skin?
-Vitamin D synthesis
-Subcutaneous fat
Calorie reserve
80% of total body fat
(in non-obese)
Hormone (leptin) release - acts on hypothalamus
→ regulates hunger & energy metabolism
What are the major roles of the skin in terms of aesthetics?
Increased risk of suicide with poor skin
Psychosexual function
B
What are the appendages on the skin?
- Pilosebaceous units ( from Latin : pilus which means hair)
- Sweat glands
- Nails
Nail plate
Nail bed(deep to plate)
Cuticle
Proximal nail fold
Onychodermal band
Lateral nail fold
Lunula-visible nail matrix
Where are terminal hairs found?
Terminal hairs → scalp, eyebrows and eyelashes
Where are vellus hairs found?
Rest of body → vellus hairs (except palms, soles, mucosal regions of lips, and external genitalia)
What is the structure of a hair?
Infundibulum
Uppermost portion of the hair follicle extending from opening of sebaceous gland to surface of the skin
Isthmus
Lower portion of upper part of hair follicle between opening of sebaceous gland and insertion of arrector pili muscle
Epithelium keratinization begins with lack of granular layer named “trichilemmal keratinization”
What are the 3 phases of the hair cycle and how long do they last?
Anagen (where new hair forms and grows)
85% of hair; lasts 2-6 years
Catagen (regressing phase)
1% of hair; lasts 3 weeks
Telogen (resting phase)
10-15% of hair; lasts 3 months
Then loss of old hair.
What is in the pilocebaceous unit and what is the function of the arrector pili?
Pilosebaceous unit: hair shaft, hair follicle, sebaceous gland
Arrector pili (smooth muscle) extends at angle between surface of dermis and point in follicle wall.
What is the difference in distribution and opening between eccrine and apocrine sweat glands?
Eccrine sweat glands
-almost everywhere on the skin
-open directly onto the skin’s surface
Apocrine sweat glands
-in areas with many hair follicles such as the scalp, armpits, groin
-open into the hair follicle
Describe the structure of the nail
Final product of proliferation and differentiation of nail matrix keratinocytes
Emerges from proximal nail fold
Grows at 1-3mm/month
Firmly attached to nail-bed
Detaches at hyponychium
Lined laterally by lateral nail folds
(Top left>Bottom right)
Proximal nail fold
Matrix
Nail bed
Nail plate
What is the only visible portion of the nail matrix
Lunula
What is the function and location of the nail matrix?
Produces nail plate
Lies under proximal nail fold, above bone of distal phalanx (to which it is connected by a tendon
Nail matrix keratinocytes differentiate → lose their nuclei and are strictly adherent - cytoplasm completely filled by hard keratins
Also contains melanocytes
C
C
D
B
A
D
D
A
C
D
D
B-pitting
Onchylosis
A
B
What kind of skin lesions are associated with psoriasis
Sharply demarcated, scaly, erythematous plaques
What is the general pathophysiology of psoriasis?
- Stressed keratinocytes release DNA / RNA
- dDCs migrate to lymph nodes
What are these lesions indicative of?
Psoriasis
What are these lesions indicative of?
Psoriasis
Outline the psoriasis therapeutic ladder?
Topical therapies
Vitamin D analogues
Topical corticosteroids
Retinoids
Topical tacrolimus / pimecrolimus
Phototherapy
Narrowband UVB
PUVA (Psoralen + UVA)
Acitretin
Systemic immunosuppression
Methotrexate
Ciclosporin
‘Advanced’ therapies
PDE4 inhibitors (Apremilast)
Biologics (anti-TNF-α, anti-IL-17, anti-IL23)
Outline the pathophysiology of eczema
Barrier defect
Filaggrin - bind and aggregate keratin bundles & intermediate filaments → form cellular scaffold in corneocytes
Reduced extracellular lipids & impaired ceramide production
Increased transepidermal water loss (TEWL)
Impaired protection against microbes and environmental allergens
Immune dysregulation
Staphylococcal superantigens stimulate Th2 lymphocyte responses and subvert T‐reg
T-cell infiltrate - bias towards Th2 responses
Role of microbiome?
Eosinophils
What are the clinical features of infantile atopic eczema?
Erythematous, oedematous papule & plaques ± vesiculation
Lichenification, crusting and excoriation and dyspigmentation postinflammatory dyspigmentation
What are these skin lesions indicative of?
Atopic eczema
What is present in this image?
Fissuring
What are these skin lesions indicative of?
Allergic contact dermatitis
What are these skin lesions indicative of?
Impetiginisation-Gold crust
Staphylococcus aureus
What is this lesion indicative of?
Venous stasis eczema
What is this skin condition called?
Erythroderma-Skin failure
What are these skin lesions indicative of?
Eczema herpeticum
-Emergency
-HSV(Herpes simplex virus)
What is the fingertip-unit guide and how much of a topical drug should you use for:
Face and neck
Back and buttocks
Chest+abdo
Entire arm and hand
Each hand
Entire leg and foot
A
