CHAPTER 14- WOUND HEALING.txt

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CHAPTER 14- WOUND HEALING.txt
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  1. Wound healing phases:
    • Inflammation (days 1-10)-
    • 1) PMNs, macrophages
    • 2) epithelialization 1-2mm/day

    • Proliferation (5 days-3 weeks)
    • 1) fibroblasts, neovascularization, production of collagen, granulation tissue

    • Remodeling (3 weeks- 1 year)
    • 1) type III collagen replaced with type I
    • 2) decreased vascularity
    • 3) net amount of collagen does not change, although significant production and degradation occurs
    • 4) collagen cross-linking occurs
  2. Inflammation:
    • 1) days 1-10
    • 2) PMNs, macrophages
    • 3) epithelialization 1-2mm/day
  3. Proliferation:
    • 1) 5 days-3 weeks
    • 2) fibroblasts
    • 3) neovascularization
    • 4) production of collagen
    • 5) granulation tissue
  4. Remodeling:
    • 1) 3 weeks- 1 year
    • 2) type III collagen replaced with type I
    • 3) decreased vascularity
    • 4) net amount of collagen does not change, although significant production and degradation occur
    • 5) collagen cross-linking occurs
    • 6) peripheral nerves regenerate at 1mm/day
  5. Order of cell arrival in wound:
    • 1) platelets
    • 2) PMNs
    • 3) macrophages
    • 4) fibroblasts
    • 5) lymphocytes
  6. Macrophages:
    are essential for wound healing (release of growth factors, cytokines, etc)
  7. Fibroblasts:
    replace fibronectin-fibrin with collagen
  8. Fibronectin
    • 1) chemotactic for macrophages
    • 2) anchors fibroblasts
  9. Thrombin and Fibrin:
    also act as growth factors for endothelial cells and fibroblasts
  10. Predominant cell type by day:
    • day 0-3: PMNs
    • day 3-4: macrophages
    • day 5-on: fibroblasts
  11. Platelet plug:
    platelets and fibrin
  12. Provisional matrix:
    • 1) platelets
    • 2) fibrin
    • 3) fibronectin
  13. Accelerated wound healing:
    reopening a wound results in quicker healing the 2nd time (as healing cells are already present there)
  14. See image on pg 66: Time-line of phases of wound healing with dominant cell type and major physiologic events
  15. Platelet granules (following slides):
    • Alpha granules
    • 1- Platelet factor 4- aggregation
    • 2- Beta-thrombomodulin- binds thrombin
    • 3- PDGF- chemoattractant

    • Dense granules
    • 1- adenosine
    • 2- serotonin
    • 3- calcium

    • 3) Platelet aggregation factors:
    • 1- TXA2
    • 2- thrombin
    • 3- platelet factor 4
  16. Other factors release from platelets:
    • 1) Platelet activating factor
    • 2) transforming growth factor alpha (TGF-alpha
    • 3) Fibroblast growth factor
    • 4) Beta lysin (antimicrobial)
    • 5) PGE2 and PGI2 (vasodilators)
    • 6) PGF2 (vasoconstrictors)
  17. Epithelial integrity:
    • 1) most important factor in healing open wounds (secondary intention)
    • 2) migration from wound edges, sweat glands, and hair follicles
    • 3) dependent on granulation tissue
    • 4) unepithelialized wounds leak serum and protein, promote bacteria
  18. Tensile strength
    • 1) most important factor in healing closed incisions (primary intention)
    • 2) depends on collagen deposition and cross-linking of collagen
    • 3) Submucosa- strength layer of bowel
    • 4) weakest time point for small bowel anastomosis: 3-5 days
  19. Myofibroblasts:
    • 1) smooth muscle cell-fibroblast, communicate by gap junctions
    • 2) involved in wound contraction and healing by secondary intention
    • 3) perineum has better wound contraction than leg
  20. Collagen Types:
    Type I- most common type of collagen: skin, bone, and tendons. Primary collagen in a healed wound

    Type II- cartilage

    Type III- Increased in healing wound, also in blood vessels and skin

    Type IV: basement membrane

    Type V- widespread, particularly found in the cornea
  21. What is rquired for hydroxylation of proline and subsequent cross-linking of proline residues? What else undergoes cross-linking?
    • 1) alpha-ketoglutarate
    • 2) vitamin C
    • 3) oxygen
    • 4) iron

    All of the above are required for hydroxylation of proline (prolyl hydroxylase) and subsequent cross-linking of proline residues.

    Hydroxylysine also undergoes cross-linking
  22. Collagen
    has proline every 3rd amino acid; also has abundant lysine
  23. Scurvy
    vitamin C deficiency
  24. Tensile strength never equal to prewound (whats the % strength)
    80%
  25. What is the predominant types of collagen and timeline:
    • 1) Type III collagen- predominant collagent type synthesized for days 1-2
    • 2) Type I collagen- predominant collagen type synthesized by days 3-4
    • 3) Type III replaced by type I collagen by 3 weeks
    • 1- at 6 weeks, wound is 80% of its final strength and 60% of its original strength
    • 2- at 8 weeks, wound reaches maximum tensile strength, which is 80% of its original strength
    • 3- maximum collagen accumulation at 2-3 weeks after that--> the amount of collagen stays the same but continued cross-linking improves strength
  26. What inhibits collagen cross-linking:
    d-penicillamine
  27. Essentials of wound healing:
    • 1) moist environment (avoid desiccation)
    • 2) Oxygen delivery:
    • 1-optimal fluids
    • 2- no smoking
    • 3- pain control
    • 4- arterial reconstruction
    • 5- supplemental oxygen
    • 6- want transcutaneous oxygen measurement (TCOM) >25mmHg
    • 3) avoid edema- leg elevation, compression
    • 4) remove necrotic tissue
  28. Impediments to wound healing:
    • 1) Bacteria >105/cm2
    • 1- decreaed oxygen content
    • 2- collagen lysis
    • 3- prolonged inflammation

    2) Devitalized tissue and foreign bodies- retards granulation tissue formation and wound healing

    • 3) Cytotoxic drugs:
    • 1- 5FU
    • 2- methotrexate
    • 3- cyclosporine
    • 4- FK-506 etc
    • can all impair wound healing

    4) Diabetes- can contribute to poor wound healing by impeding the early-phase response

    5) Albumin <3.0- risk factor for poor wound healing

    6) Steroids- prevent wound healing by inhibiting macrophages, PMNs, and collagen synthesis by fibroblasts; decreases wound tensile strength as well

    7) Vitamin A (25,000 IU qD)- counteracts effects of steroids on wound healing

    • 8) Wound ischemia
    • 1- fibrosis
    • 2- pressure (sacral decubitus ulcers
    • 3- poor arterial inflow
    • 4- poor venous outflow
    • 5- smoking
    • 6- radiation
    • 7- edema
    • 8- vasculitis
  29. Diseases associated with abnormal wound healing (following slides)
  30. Osteogenesis imperfecta
    type I collagen defect
  31. Ehlers-Danlos syndrome
    • 1) 10 types identified
    • 2) all collagen disorders
  32. Marfan's syndrome
    fibrillin (collagen) defect
  33. Epidermolysis bullosa:
    • 1) excessive fibroblasts
    • 2) Tx: phenytoin
  34. Scurvy
    vit C deficiency
  35. Pyoderma gangrenosum:
    • cause not clear.
    • Pyoderma gangrenosum is a disease that causes tissue to become necrotic, causing deep ulcers that usually occur on the legs. When they occur, they can lead to chronic wounds. Ulcers usually initially look like small bug bites or papules, and they progress to larger ulcers. Though the wounds rarely lead to death, they can cause pain and scarring.
  36. Diabetic foot ulcers:
    • 1) charcot's joint (2nd MTP joint)
    • 2) secondary to neuropathy
    • 3) pressure leads to ischemia
  37. Leg ulcers:
    • 1) 90% of leg ulcers due to venous insufficiency
    • 2) Tx: unna boot, elastic wrap
  38. Scars
    • Contain a lot of:
    • 1- proteoglycans
    • 2- hyaluronic acid
    • 3- water

    • 2) Scar revisions- wait for 1 year to allow maturation; may improve with age
    • 3) Infants heal with little or no scaring
  39. Cartilage:
    contains no blood vessels
  40. What effect does denervation have on wound healing?
    denervation has no effect on wound healing
  41. Chemotherapy
    has no effect on wound healing after 14 days
  42. Keloids
    • 1) autosomal dominant
    • 2) dark skinned
    • 3) collagen goes beyond scar
    • 4) Tx:
    • 1-XRT
    • 2- steroids
    • 3- silicone
    • 4- pressure garments
  43. Hypertrophic scar tissue:
    • 1) dark skinned
    • 2) flexor surfaces of upper torso
    • 3) collagen stays within confines of scar
    • 4) often occurs in burns or wounds that take a long time to heal
    • 5) Tx: steroids, silicone, pressure garments

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