Wound healing

  • 3 stages
    • Inflammatory stage
      • Clot formation
      • Neutrophils are first to arrive
      • Macrophages are the key players
    • Proliferative phase
      • Starts around week 2
      • Fibroplasia: Formation of granulation tissue: sequence of formation: fibronectin → collagen III → collagen I
      • Neovascularization: endothelial cells project pseudopods through the basement membrane: IL-6 → NO → VEGF
    • Remodelling
      • Epithelialization
        • Occurs hours after injury from epithelial structures
        • If basal layer lost, collagen V, fibrin and fibronectin act as provisional matrix
      • Scar strength
      • 5% at 1 week
      • 20% at 3 weeks
      • 80% at 1 year
Other cells of importance
  • Langerhans Cells
    • Antigen presenting cells
    • originate from precursors in the bone marrow
    • Found in epithelial tissue and lymph nodes
    • Recognize, uptake, process and present antigens to T cells (CD4)
    • Cell is responsible for initial sensitization of the T-cells
    • Impaired by UCR
    • Disease processes involving Langerhans Cells
      • All S-100 and CD1a+ with Birbeck granules in cytoplasm
      • Letterer-Siwe disease
      • Hand-Schuler-Christian
      • Eosinophilic granuloma
      • Hashimoto-Pritzker
    • Can be infected with HIV
    • Produces IL-1, expresses E-Cadherin (to adhere to KC)
    • Expresses CD1a
    • Mostly suprabasilar layer
    • Birbeck granules on electron microscopy
  • Glomus Cells
    • Derived from Suquet-Hoyer canals
    • Vascular smooth muscles
    • Active in shunting blood from Arterial to Venous to bypass capillaries
    • Mostly in hands and feet
      • Nails
    • Glomus tumors and glomangiomas
  • Merkel Cells
    • Basal layer
    • Mechanoreceptor
    • Connection with neurons
    • Stain with cytokeratin 20
      • Metastatic oat cell carcinoma looks the same but stains negative for cytokeratin 20 and is positive with TTF-1
    • Merkel Cell Carcinoma is associated with polyomavirus
  • Mast cells
    • Greatest density in the papillary dermis
      • Around vessels, appendages
    • Derived from bone marrow-residing CD34+ stem cells
      • No CD11c or CD6 like monocytes, macrophages and dermal dendrocytes
    • Diseases: mastocytosis, UP, TMEP
    • Proliferation depends on the c-kit receptor and its ligand stem-cell factor (SCF)
      • Mutations: Piebaldism and mastocytosis
    • Preformed mediator in mast cell - serine proteases (tryptase), heparin, histamine
    • Produce IL-8 (potent neutrophil chemotactic agent)
      • This is why urticaria which is an invisible dermatosis can have neutrophils and anti neutrophilic drugs like dapsone and colchicine can have a play here
    • Stain + Giemsa or Leder stains