Skin/integument system

Skin/integument system

1. Epidermis

   • epithelial layer of ectodermal origin - derivates like hair, nails, sweat and sebaceous glands
   • stratified squamous keratinized epithelium
     • mostly: keratinocytes
     • less abundant: Melanocytes
       • produce pigment
       • Langerhans cells: APC
       • Merkel cells
         • tactile epithelial cells
       • keratinocyte melanin content + carotene + number of blood vessels in dermis = determine skin colour
       • eumelanin = brown/black pigment produced by melanocyte - found in basal layer of hair follicles, red hair = pheomelanin
       • neural crest derivative -> embryonic epidermis stratum basale
       • pale-staining, rounded cell bodies attached by hemidesmosomes to the basal lamina, but lacking attachments to the neighboring keratinocytes.
       • long cell bodies penetrate epidermis, invaginations into keratinocytes
     • epidermis forms major distinction between THICK(palms and soles) AND THIN SKIN(everywhere else)
     • lacks microvasculature therefore receives O2 by diffusion from dermis
       • from dermis - epidermis: 4 LAYERS
         • 1 - Basal layer/stratum basale
           • basophillic cuboidal layer on basement membrane of dermal-epidermal junction - hemidesmosomes in basal cell membranes join these cells to basal lamina - intense mitotic activity - progenitor cells - basal stem cells for keratinocytes
           • Keratins
             • intermediate filaments of 10 nm diameter
         • 2 - spinous layer/stratum spinosum
           • THICKEST LAYER polyhedral cells central nuclei + nucleolus synthesizing keratins
           • stratum geminativum: above basal layer some cells may still divide and combined zone = this
             • filaments assemble to tonofibrils
               • terminate at: desmosomes - holding cell layers together
         • 3 - Granular layer/stratum granulosum
           • keratinisation
           • keratohyaline granules: fllaggrin and other keratin proteins associated with tonofibrils
           • lamellar granules
             • under
             • exocytosis - producing impermeable layer around cells preventing water loss
         • 4 Stratum lucidum - THICK SKIN, and stratum corneum
           • lucidum = translucent layer of flattened eosinophillic keratinocytes corneum = 15-20 layers of squamous keratinsed filaments
           • squames = fully keratinised, continously shed at epidermal surface as desmosomes break down

2. Dermis

   • Mesodermal connective tissue
   • Under dermis: subcutaneous tissue/hypodermis

3. Dermal papilla (between them)

   • Irregular junction between them, with interdigitating epidermal ridges - strengthening layers
     • Dermal epidermal junctions - peg and socket variety + distinctive for fingerprints etc