2: Principles of Wound Healing - Bennett Flashcards
phases of wound healing
(injury)
inflammatory
proliferative
maturation
mechanisms of wound repair
- connective tissue deposition
- epithelization
- contraction
types of wound closure
- primary intention
- secondary intention
- delayed primary closure
- partial thickness (scratch or superficial abrasion)
characterized by hemostasis and inflammation
inflammatory phase
- collagen exposed, during wound deformation activates the clotting cascade
- damaged cells release thromboxane A2 and prostaglandin 2 alpha (vasoconstrictors)
- initial response limits the hemorrhage
- capillary vasodilation occurs due to histamine release and the inflammatory cells migrate to the wound bed
first response cell
platelets
- release epidermal growth factors, platelet derived growth factors, histamine
- stabilie wound through clot formation
EGF and PDGF regulate …
EGF - cell growth, proliferation and differentiation
PDGF - cell growth and division of blood vessels
vessel adherence
diapedesis
chemotaxis
phagocytosis
- pavementing, margination
- movement through vessel walls
- chemical directive to injury site
- opsinization
- PMN (second response) migrate to wound for complement mediated opsonization of bacteria
most essential cell for wound healing
macrophages
- macrophages release TNF which stimualtes fibroblasts and angiogenesis
- TGF stimulates keratinocytes
increased blood flow and congestion is evident by increased number of red cells
inflammatory phase
- the increase in PMNs is also evident as well as increased prtn exudates
3 parts of proliferative phase
- epithelization
- angiogenesis
- collagen deposition
basement membrane damaged v. not damaged
intact = cells migrate in normal pattern, normal layers of epidermis restored in 2-3 d
destroyed = re-epitheliaztion from cells in periphery
what stimulates angiogensesis?
TNFalpha
- endothelial cell migrationa nd capillary formation
- maintains granular bed
- mmigration of capillaries delivers nutrients to wound bed
cytokines involved in granulation tissue formation during proliferative phase
- fibroblasts differentiate and lay down collagen fibers in varying patterns
- IGF, PDGF
histological features of proliferative phase
numerous fibroblasts
new capillary formation
describe maturation phase
- increased collagen and vascularity
- wound contraction
- wound reaches max strength at one year
- has tensile strength 30% of normal skin
major cells each phase
inflammation- neutrophils
proliferation - macrophages
maturation - fibroblasts and endothelial cells
4 wound healing principles
- vascular perfusion
- bacterial balance
- nutritional balance
- control contributing factors
parting of layers of surgical wound
wound dehiscence
due to: infection, hematoma, seroma, poor surgical technique, inappropriate closure technique, excessive motion at surgical site, pt non-compliance
side to side closure of wound
primary intention
ex: use sutures to reapproximate skin edges
wound is left open to granulate to closure
secondary intention
wound is left open for a period of time and then primarily closed
delayed primary closure
abnormal scar that extends beyond boundary of original skin injury
keloid
- raised, thickened growth associated with pruritus and pain
- scanning electron microsocopy reveals randomly organized collagen fibers in dense connective tissue matrix
- sternum, deltoid, upper back have increased susceptibility (elevated m and skin tension), also earlobes and post portion of neck
- 50% recurrence
- tx with compressive dressings, intralesional corticosteroid injections, cryosurgery, laser ablation
widened or unsightly scar that does not extend beyond original boundaries of wound
hypertrophic scars
- usually reach a certain size and then stabilizes or begins to regress
