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Updated: Jul 12 2018

Skin Anatomy and Wound Healing

  • Anatomy
    • Epidermis
      • function
        • protection, temperature regulation, moisture retention
      • major cell types
        • keratinized squamous epithelial cells, melanocytes
      • layers (top to bottom):
        • stratum Corneum
        • stratum Lucidum
        • stratum Granulosum
        • stratum Spinosum
        • stratum Basale (contains pluripotent stem cells)
        • "CaliforniansLike Girls inString Bikinis"
      • from basale to corneum, cells mature, lose their organelles, become keratinized
    • Dermis
      • function
        • structure, sensation, wound healing
      • contains hair follicles, sebaceous glands, specialized nerve endings, vasculature
        • compression of vasculature can lead to pressure ulcers
        • neoplasm of glomus apparatus can lead to glomus tumors
      • mostly made up of extracellular matrix
        • collagen, glycosaminoglycans, proteoglycans, glycoproteins
      • major cell types
        • fibroblasts, Langerhans cells, pluripotent stem cells (in hair follicles), endothelial cells
      • layers (top to bottom)
        • papillary dermis
        • reticular dermis
    • Subcutaneous tissues
      • consist of fat, muscle, tendon, ligament, bone, etc.
    • Exocrine glands
      • glands that retain ducts to body surfaces
      • 3 types, based on the manner in which they secrete substances
        • merocrine
          • cells form membrane-bound secretory vesicles internal to the cell and move to the apical surface of the cell to release contents
            • most glands
        • apocrine
          • cells in which the apical portions of cells are pinched off and lost during the secretory process, resulting in secretory products that contain a variety of molecular components including those of the membrane
            • i.e., mammary glands
        • holocrine:
          • involves death of the cell
          • secretory cell is released, and as it breaks apart, the contents of the cell become the secretory product.
            • i.e. sebaceous glands, sweat glands located in the axillae, pubic areas, around the areoli of the breasts
  • Normal Wound Healing
    • Phases: not discrete, but rather overlapping
      • hemostasis (1 - 24h)
        • endothelial damage leads to exposure of the basement membrane, activation of intrinsic and extrinsic coagulation cascade, and ultimately deposition of fibrin with creation of a platelet plug
        • platelets are integral to initiating wound healing
          • they release cytokines that cause leukocyte migration and chemotaxis into the wound
      • inflammation (1 - 5d)
        • mast cells
          • native cells initiate the inflammatory phase
          • secrete cytokines that cause vasodilation and increase vascular permeability
          • allows influx of neutrophils and macrophages to the wound bed
        • neutrophils
          • present early in inflammatory phase
          • clear intralesional pathogens
          • prepare the wound bed by removing damaged cells
          • secrete cytokines that stimulate infux of macrophages
        • macrophages
          • present late in inflammatory phase
          • early on act in coordination with neutrophils to phagocytose bacteria and dead cells
          • secrete cytokines and growth factors that drive fibroblast proliferation and angiogenesis
          • act to downregulate the initial infammatory response
      • proliferation (4 - 21d)
        • fibroblasts lay down type III collagen
        • myofibroblasts (fibroblasts with contractile filaments) initiate wound contraction
        • angiogenesis and vasculogenesis lay down new blood vessels
        • granulation tissue (newly laid collagen with neovascularization) forms
        • epithelialization occurs from surrounding basal keratinocytes and hair follicle basal cells
      • maturation (21d to up to 1 year)
        • type III collagen remodeled to type I collagen
        • vessels mature and excess vasculature involutes
        • erythema and raised appearance of wound resolves
  • Types of Wound Healing
    • Primary intention
      • wound edges are approximated
      • grafts and flaps are considered primary closure
    • Secondary intention
      • wound edges are left open and allowed to fill in
    • Tertiary intention
      • wound edges are left open and allowed to granulate and are approximated and closed at a later time
        • aka delayed closure
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