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SKIN (specialization (Eccrine (regualr) Sweet Glands (Tubules (contractile…

- - - - 'hair root' (epidermal)
        
        'dermal papilla'
        
        supplies blood vessels and nerves
    - - outer
        
        modified stratum basale + stratum spinosum
    - - differentiating stratum granulosum-like cells
        
        cell that produce very order/regulary
        
        move inward and die
        
        to produce hair shaft
    - - smooth muscle fiber anchor the dermal CT that surround hair follicles
      - involuntary automic control
  - - - secretes lipid-rich sebum
      - staining by H&E stain: light
    - - all contents releaseda
        
        holocrine secretion
    - - ducts obstruction - bacterial infection
  - - - secrete the watery serous secretions
        
        'sweat'
    - - chloride channel @ apical
      - move salt to lumen --> move water down (osmotic gradient)
    - - contractile cells embedded
      - epithelial/ectodermally derived;
      - help expel secretory products into ducts efficiently
      - 'myoepithelial' cells
    - - secrete small amounts of protective mucous content
      - regular, polarized, exocytosis-based secretion
      - Eccrine secretion
- - - - outer
        large majority of keratinocytes (from ectoderm)
        
        Avascular
      - stratifies squamous keratinized epithelium (squams)
      - rise to specialized skin appendages
        
        sweet & sebaaceour gland, hairfollicles etc
      - specialized cell types
        
        melancytes
        
        merkel cell
        
        Langerhans cells
    - - under
        
        Dense irregular CT (mesoderm)
        
        vascularized (have blood vessel)
      - Nerves and specialized sensory nerve endings/receptors Location
        
        @ dermal ridges/papillae
        
        (Meisner's corpuscles)
        
        temperature, pain and
        touch
        
        @ deep, reticular layer of the dermis
        
        (Pacinian corpuscles)
        
        pressure
      - 'Arrector pili'
        
        smooth muscles that attach to hair follicles
    - - Deep: a mixture of loose CT & adipose tissue
        (it connects the skin to underlying tissues)
- - - - ectodermally derived
  - - - undifferentiated, stem cells
        
        considerable mitotic activity
      - cuboidal to low columnar epithelial cells/keratinocytes
      - desmosomes (some)
        
        @ cell-cell interfaces
      - hemidesmosomes (lots)
        
        @ cell-basement membrane interface;
        
        attachment of epidermis to the dermis
        
        maintenance of the stem cell
        phenotype
      - contain
        
        melanocytes
        
        produce skin pigment
        
        neural-crest derived
        
        migrate into the epidermis
        
        reside in the stratum basale
        
        tyrosine
        
        Merkel cells
        
        receptors of mechano/touch
        
        neural- crest derived
        
        migrate into the epidermis
        
        reside in the stratum basale
      - when basal keratinocytes detach from the basement membrane and move up into the next stratum they begin to differentiate
    - - start differentiation of the epithelial keratinocytes
      - spines
        
        many desmosomes at all cell-cell contact points at the ends of small keratinocyte cell processes
      - tonofilaments
        
        keratin intermediate filaments
      - Langerhans cells
        
        antigen-presenting cells (APC's)
        
        dendritic
        
        start immunochemical respond
        
        like marophage & engulf pathogen
        
        hematopoietic stem cell-derived
        
        migrate into the epidermis
        
        1st reside in the stratum spinosum
        
        immunochemical stain only - CD1A
      - melanocyte
        
        melanosome
        
        membrane-bound vesicles, contain UV-light absorbing melanin
        
        membrane-bound vesicles, contain UV-light absorbing melanin
        
        derived from neural-crest
        
        produce skin pigment
        
        migrate into the epidermis
        
        reside in the stratum basale
    - - fully differentiate cell
        
        flatten/become squamous
      - generate lipoprotein (lipid-rich) vesicles/granules
        
        (lipid is exocytosed )
      - 'keratohyalin'
        
        glycoproteinacious complex
        
        forms cytoplasmic 'granules' (not membrane-bound)
        
        cross-links the keratin tonofilaments together
      - waterproof barrier
        
        b/w s. granulosum and s. lucidum above
    - - cells fully differentiate
      - 'eleidin'
        
        glycoproteinaceous complex
        
        aligns the cross-linked keratin tonofilaments in parallel arrays
      - cells are above the waterproof barrier
        
        cell start to die and lose their nuclei
    - - Enucleated flat cells
        
        completely dead
      - 'squames' 鳞屑
        
        filled with protective cross-linked and bundled keratin filaments
      - 'desquamated'
        
        desmosomes deteriorate 恶化
        
        squames slough-off/released