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Skin-nontumor / Clinical Dermatology

General

Normal epidermis

Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC, Memorial University of Newfoundland (see Reviewers page)
Revised: 24 August 2011, last major update August 2010
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Micro description
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● Epidermis is outer layer of skin
● Inner layers are dermis and subcutaneous tissue
● Superficial fascia marks deep boundary between skin and underlying soft tissue
● Epidermis forms outer layer of keratin that is protective and waterproof
● Cells present include melanocytes, keratinocytes, Langerhans’ cells and Merkel cells
● Skin is thicker in palms and soles, which contain epidermal ridges that prevent slipping and form fingerprints and footprints
● Epidermis is composed of stratified squamous epithelium containing keratinocytes in 4 layers: inner basal, squamous, granular and outer cornified
● Keratinization takes 30-45 days; alterations in pattern and speed cause dermatoses, hyperkeratosis or parakeratosis

● Basal layer:
 - Mitotically active, produces other keratinocytes
 - Contains low molecular weight keratin
 - Separated from dermis by continuous basal membrane; keratinocytes are attached to this membrane by hemidesmosomes
 - Also contains melanocytes

● Squamous layer (stratum spinosum):
 - Also called prickle or malpighian layer
 - Has several layers of cells, larger than basal layer, which become flat and eosinophilic as they approach the surface due to an increase in keratin and reduction in ribosomes
 - May have clear vacuolated cytoplasm
 - Cells are attached to each other by fine spiny bridges with central dot-like desmosomes (Bizzozero’s nodule)
 - Loss of spiny bridges causes acantholysis

● Granular layer (stratum granulosum):
 - 1 to 3 layers of flattened cells with intensely basophilic keratohyaline granules, which contain precursors of filaggrin protein, which causes aggregation of keratin filaments

● Stratum lucidum:
 - Present only in soles and palms, between granular and cornified layer
 - Homogenous eosinophilic zone

● Cornified layer (stratum corneum):
 - Also called horny layer
 - Basket weave pattern of multiple layers of polyhedral cells without nuclei
 - Region is thicker and more compact in acral region [peripheral body-limbs, fingers, ears]

● Rete ridges:
 - Undulating forms of epidermis and dermal papillae at dermoepidermal junction  - Flattens with aging

Drawings
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Layers

Micro images
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Skin


   

Minimal and intense melanin pigment within basal cells

Intraepithelial sweat gland

End of Skin-nontumor / Clinical Dermatology > General > Normal epidermiss

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