Updated: 7/12/2018

Skin Anatomy and Wound Healing

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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)
      • "Californians Like Girls in String 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.esebaceous 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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Questions (2)
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(M2.DM.17.4765) A 79-year-old male presents to the emergency room with difficulty breathing, productive cough, and fever for several days. He has a history of chronic obstructive pulmonary disease (COPD), type II diabetes mellitus, and hypertension. After initiation of oxygen by nasal cannula, albuterol and ipratroprium nebulizers, a chest radiograph is obtained. The results are shown in Figure A. The patient is admitted to the hospital for antibiotic therapy. On the second day of his hospital course, he becomes tachypneic and desaturates, and the decision is made to transfer him to the intensive care unit and intubate him. He remains sedated on the ventilator for the next week as his respiratory infection is treated, and he is started on total parenteral nutrition. On his eighth day in the hospital, his nurse notes that his heel appears as in Figure B. At this time, the patient’s temperature is 99.8°F (37.7°C), blood pressure is 119/65 mmHg, pulse is 85/min, and respirations are 13/min on the ventilator. Which of the following is the best next step in management?

QID: 109026
FIGURES:
1

Frequent repositioning

77%

(30/39)

2

Topical lidocaine

0%

(0/39)

3

Zinc supplementation

3%

(1/39)

4

Initiate intravenous vancomycin

10%

(4/39)

5

Obtain foot MRI

10%

(4/39)

M 7 E

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