Skin Histology Epidermis J.F. Thompson, Ph.D. Chapter 5 Skin Histology Epidermis J.F. Thompson, Ph.D.

The Architecture of the Skin 2 Principal portions Epidermis - epithelium Dermis – areolar and dense irregular fibrous connective tissue Hypodermis “beneath the dermis” the subcutaneous layer next to: adipose layer or muscle or bone

The Epidermis Stratified Squamous Epithelium 4 cell types Keratinocytes - 90% filled with keratin (protein) waterproof barrier Melanocytes - 8% produce melanin (pigment) pass melanin to keratinocytes Langerhans cells phagocytes (from immune system) easily damaged by UV light Merkel cells in deepest layer of hairless skin sensory transduction - touch

Keratinocytes and Melanocytes

Merkel Cells

Langerhans Cells

Epidermal Cell Layers Stratum basale Stratum spinosum A single layer of cuboidal/columnar cells Stem cells, melanocytes, Merkel cells Stem cells  keratinocytes, mitosis pushes the other layers to the top Stratum spinosum 8 to 10 layers of closely packed cells Cell junctions - spot desmosomes Langerhan’s cells

Epidermal Cell Layers Stratum granulosum Stratum lucidum 3-5 layers of flattened, with keratohyaline granules beginning breakdown of nucleus, cell death initiated Stratum lucidum only in thick skin (palms, feet) 3-5 layers of clear, flat dead cells with keratin Stratum corneum 20-30 layers of flattened, dead, keratin-filled cells continuously shed and replaced 2-4 weeks for each cell to form and to move from the stratum basale to the surface

Thin Skin

Thin Skin Stratum Corneum Stratum Granulosum Stratum Spinosum Stratum Basale

Thick Skin

Skin Histology Epidermis End Ch 5 Skin Histology Epidermis