Epidermis and Disorders of Kertatinization Flashcards
Layers of the epidermis
- Stratum basalt
- Stratum spinosum
- Stratum granulosum
- Stratum corneum
Basal layer
Stratum basale
Cuboidal cells with proliferative function
Adhere to basement membrane via hemidesmosomes
Spinous layer
Stratum spinosum
Bind to neighboring keratinocytes via desmosomes (spiny when histology ally treated)
Cells migrate to surface and lose water and flatten
Desmoglein
Transmembrane proteins that connect desmosomes
Antibodies to desmogleins can lead to loss of cellular adhesion and blister formation
Desmoglein 1
Localized to entire epidermis but especially in upper layers
Desmoglein 3
Localized to basal layer
Langerhans cells
Macrophages in epidermis Found in spinous layer Derived from bone marrow Immunomodulatory role Allergic contact dermatitis, graft-versus-host disease and drug eruptions
Granular layer
Stratum granulosum
2-3 cells thick
Keratohyaline and lamellar granules
Keratohyaline granules
Contain profilaggrin and keratin filaments
Profilaggrin
Associated with intermediate filaments
Made up of filaggrin, which promotes aggregation and stabilization of int. filaments in corneum
Lamellar granules
Aka Odland bodies Contains lipids, free sterols, hydrolases and ceramides -barrier function -apoptosis -desquamation
Cornfield layer
Stratum corneum
Anucleate cells no longer mitotically active
Not on mucosal surfaces
Lines of Blaschko
Linear and whirled pattern keratinocytes follow as they migrate during embryogenesis from dorsal neural crest to the ant. midline of skin and to extremities
Keratin Structure
intermediate filament makes up cytoskeleton
- alpha helical structures
- 2 types: type1 (acidic) and type2 (basic)
- type1 and 2 assemble into heteropolymers, which align to form keratin filaments
- insert into desmosoems and hemidesmosomes
Keratinization
aka cornification (takes 12-14 days)
- enlarge and flatten keratinocytes as migrate towards surface
- filaggrin-induced keratin filament parallel assembly and cross-linking of proteins to form cornified envelope
- release of lamellar granule lipids to form hydrophobic barrier
- degradation of cellular organelles to form anucleate cells
- apoptosis
Desquamation
Shedding of corneocytes (takes 12-14 days)
- hydrolases divide proteins linking adjacent cells
- active when stratun corneum well-hydrated
- disruption results in xerosis (dry, rough, scaly skin)
Xerosis
dry, rough, scaly skin
- due to decrease in intracellular lipids and NMF, failure of adherent bonds of stratum corneum to break down, and dehydration of corneocytes
- stratum corneum becomes less pliable and more susceptible to small fissures and formation of dry scale
- may req assessment of medication, renal function and overall nutritional status
Natural Moisturizing Factors (NMF)
free amino acids, lactic acid, urea and salts
- hygroscopic
- accounts for pliability of the epidermis
Atrophy
decreased cell proliferation
-thinning of skin
Hyperplasia
increase in thickness of tissues
- Acanthosis - proliferation of stratum spinosum
- Hyperkeratosis - thickening of stratum corneum due to increase production of corneocytes or reduced desquamation
- Lichenification - thickening of stratum spinosum and corneum in response to repeated scratching and rubbing
Wound healing
intermediate filaments associate with actin and tubulin, allowing the keratinocyte to migrate
- 12 hrs after wound, epidermal keratinocytes flatten and lose bond with BM and dermis
- keratinocytes migrate across wound by forming a “train”
- moist wound environment helps
Disorders of Cornification
- defects in keratinocytes
- disrupted intercellular cohesion
- abnormal lipid function
Icthyosis vulgaris (IV)
most common disorder of cornification
- retention hyperkeratosis
- failure of cellular signals to trigger corneocyte shedding
- autosomal dominant with variable expression
- trunk and extremities favored with fish scale
- mild itching
- commonly associated with atopic triad
- some keratosis pilaris
- hyperlinear palms
- exacerbated by cold weather and decreased humidity
Keratosis pilaris
follicular retention hyperkeratosis overlying hair follicles on extensor upper and lower extremities and buttocks
Palmoplantar Keratoderma (PPK)
hyperkeratosis of palms and soles
- autosomal dominant AND recessive inheritance patterns
- due to keratin mutations, resulting in abnormal type1 and type2 pairings of keratins
- 3 categories:
1. diffuse (thick, yellow plaques of entire palm/sole, border may be red and patients may complain of hyperhidrosis)
2. focal (hyperkeratosis localized over pressure points)
3. punctate (hyperkeratotic papules and nodules, commonly misdiagnosed as warts) - treatment: pare hyperkeratotic areas and using topical moisturizers and humectants
Diseases characterized by altered epidermis
increased inflammation or exposure to toxin
Atopic Dermatits
eczema: common rash occurring with atopic triad (asthma, eczema, and allergic rhinitis)
- genetic influence
- due to increased inflammation in the skin
- filaggrin defect: mutation causes loss of function, resulting in cell envelope missing protein and subsequent reduction in amino acids, causing dehydration of corneum
- epidermis loses capacity for maintenance of barrier
Psoriasis
inflammatory skin disease
- red plaques, thick and adherent scale and nail changes
- inflammation stimulates shortened cell turnover time (increased proliferation rate), with 4 day transit time
- cornified layer unable to compensate, resulting in thick, erythematous plaques with adherent scale
Staphylococcal Scalded Skin Syndrome (SSSS)
rare, prodome of malaise, irritability, fever and skin pain
- redness starts with head then spreads
- flaccid bullae develop over involved sites, followed by widespread desquamation over 3-5 days
- caused by exotoxin secreted by phage group II s. aureus
- Exfoliative toxins (ET-A and ET-B) target desmoglein 1 and lead to loss of cell-cell adhesion
- toxins renally excreted so renal failure and immunosuppression/
Treatment of disorders of cornification/xerosis
- avoid hot and prolonged showers (lukewarm water)
- use mild soaps/soapless cleansers
- avoid products with fragrances
- do not scrub skin with washcloth nor loofah
- pat dry with towel and apply emollients immediately
- moisturizing creams or ointments preferred over lotions
- humidifiers ma help minimize xerosis in winter
- inflammatory skin diseases (eczema and psoriasis) benefit from topical steroid to reduce inflamation and allow healing of cutaneous barrier
Emollients
moisturizers - topical products that hydrate skin
- lotions, creams, ointments
- absorb into epidermis and enhance moisture retention
Humectants
agents that pull water into cells
- ammonium lactate, urea creams
- disorders of cornification require these
