Updated: 1/28/2018

Skin Anatomy and Wound Healing

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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
    • 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
    • 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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