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Updated: Apr 30 2022

Skin Anatomy and Wound Healing

  • Snapshot
    • A 25-year-old African American woman presents to her dermatologist for a bothersome scar. She reports that a few months ago, she injured her arm after falling off a bike. Since then, her cut has healed and a raise flesh-colored scar has grown over the wound. It is often itchy or even painful. On physical exam, she has a 7 cm raised scar with irregular borders that extends beyond the original wound. (Keloid)
  • Overview
    • Skin is the largest organ of the body
    • Functions
      • photoprotection
      • barrier formation
      • homeostasis
      • thermoregulation
      • immunologic protection
    • Skin is made of the epidermis and dermis
  • Anatomy
    • Epidermis
      • layers from top to bottom
        • stratum Corneum
          • serves as a physiologic barrier from
            • chemical and microbiologic invasion
            • fluid and solute loss
        • stratum Lucidum
        • stratum Granulosum
        • stratum Spinosum
        • stratum Basale
          • separates the epidermis and dermis
        • Californians Like Girls in String Bikinis”
      • major cells
        • keratinocytes
          • mature from the stratum basale to the stratum corneum over the course of 4 weeks
        • melanocytes
          • produces melanin, which protects the skin from ultraviolet radiation
        • Langerhan cells
          • immune cells that present antigens
        • Merkel cells
          • contain neuroendocrine peptides
    • Dermis
      • layers from top to bottom
        • papillary dermis
        • reticular dermis
      • functions as structural support and provides nutrition via the vasculature
      • contains subdermal epithelial structures
        • sebaceous glands
        • apocrine glands
        • hair follicles
        • nerves
  • Normal Wound Healing
    • Wound disrupts structure and function of epidermis
    • Activates keratinocytes, fibroblasts, endothelial cells, platelets, and macrophages
    • Hemostasis and inflammatory phase (0-3 days)
      • clot forms with platelet aggregation, trigger of clotting cascade, and small vessel constriction
      • mast cells release histamine and other vasodilators to increase permeability in vasculature
      • neutrophils and other inflammatory cells migrate into tissue
        • edema or swelling is seen clinically
      • macrophages clear debris
    • Proliferative phase (3 days to weeks)
      • fibroblasts
        • deposits glycoprotein and mucopolysaccharides
        • produce myofibroblasts
          • myofibroblasts help to contract the wound to pull the edges together
        • synthesize collagen (type III)
          • the resulting collagen matrix stimulates angiogenesis
      • keratinocytes re-epithelialize the wound
      • the resulting collagen deposition and angiogenesis form granulation tissue
      • abnormal wound healing in this phase
        • deficiency in vitamin C or copper can result in delayed wound healing
        • keloids and hypertrophic scars may result from persistent myofibroblasts or excessive matrix synthesis
    • Remodeling (weeks to months)
      • type III collagen is replaced by type I collagen, resulting in increased tensile strength of the tissue
        • hypertrophic type 1 collagen deposition can result in formation of a contracture
      • vessels mature
      • remodeling is mediated by fibroblasts
      • abnormal wound healing in this phase
        • deficiency in zinc can result in delayed wound healing
  • Wound Closure Intentions
    • Primary intention
      • wound edges are re-approximated
      • faster healing and less scarring
    • Secondary intention
      • wounds are left open and allowed to granulate and fill in over time
    • Tertiary intention (delayed closure)
      • wounds are left open and observed
      • wounds are then approximated and closed later
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