Skin Wound Healing 2 Flashcards
what does skin wound healing involve (2)
- epithelial regeneration
- formation of connective tissue scar
what is a primary closure and recommendations to treat
clean or clean-contaminated wound converted to clean wound
immediate suture closure without tension
what is delayed primary closure and recommendations to treat
clean-contaminated or contaminated wound with questionable tissue viability, edema, skin tension
performed 2-5 days after injury; tissue debridement and wound lavage before closure
what is secondary closure and recommendations to treat
contaminated or infected would
performed at least 5 days after injury; granulation tissue and epithelized skin edges excised at the time of closure
what is second intention healing
wound tissue unsuitable for closure; large skin defect and/or extensive tissue devitalization
healing by granulation tissue, wound contracture and epithelialization
what are the 3 phases of wound healing
- acute inflammation: 0-4 days
- proliferative phase: 2 days to several weeks (new blood vessels form –> angiogenesis, migration and proliferation of fibroblasts)
- remodelling phase: begins at 1 week and continues up to 2 years (maturation, contraction)
what do the phases of wound healing look like
how is hemostasis acheived in the inflammatory phase
hemostasis –> achieved by compression of vessels due to soft tissue swelling & formation of fibrin-platelet plug within the wound defect
how is the inflammatory phase directed and amplified
by activated platelets within fibrin plug (wound repair mediators released from storage granules)
neutrophils, macrophages and fibroblasts can bind selectively to wound matrix as they migrate into the wound (initiate immune and synthetic functions)
what is the proliferative phase and what occurs
angiogenesis = neovascularization
new vessels are leaky –> granulation tissue is often edematous
edema can persist long after the acute inflammation has resolved
what is granulation tissue
tissue repair begins within 24 hours
granulation tissue forms 2-5 days (angiogenesis, fibroblast migration and proliferation into the injury site, ECM deposition)
pink, soft, granular gross appearance
what does granulation tissue produce
increase in blood vessels
fibroblasts (elongate nuclei)
what occurs during the remodelling phase
granulation tissue progressively accumulates collagenous
acts as scaffold for formation of scar tissue
what is the difference between granulation tissue and mature scar tissue
granulation tissue: loose connective tissue with edema
mature scar tissue: dense collagenous tissue
what is the process of scar formation
as healing progresses –> numbers of proliferating (active) fibroblasts –> blood vessels (vascular regression) = pale
what is healing by first intention (primary closure/primary union)
a clean, uninfected surgical incision closed with sutures
only focal disruption of epithelial basement membrane
death of only small numbers of epithelial and connective tissue cells
epithelial regeneration predominates over fibrosis
what occurs 24 hours to 7 days in first intention healing
neutrophils migrate into fibrin clot –> then macrophages
- basal cells at cut edge of epidermis begin to show mitotic activity
- epithelial cells start to migrate and proliferate across the dermis –> deposit BM as they progress, meet in midline under a scab, epidermis is thickened (hyperplastic)
- fibroblasts migrate in –> proliferate, start to produce collagen, blood vessels form = granulation tissue
what occurs in the early weeks healing by first intention
- continued collagen accumulation
- fibroblasts start to reduce in #
- decrease in leukocytes, edema, vascularity
- balancing –> increasing collagen, vascular regression
- sutures out at 10 d (epidermis shoudl be intact)
- few to no inflammatory cells –> will be reaction around sutures
what occurs in months to years after healing by first intention
- scar = dense connective tissue, covered by essential normal epidermis (gradually increases in strength)
- dermal appendages that that were destroyed (hair follicles are permanently lost)
what occues in healing by second intention
tissue loss more extensive
abscesses, ulceration, larger wounds (more intense inflammation, abudnant granulation tissue, wound contracts by action of myofibroblasts)
what are the features of CT in healing by second intentions
connective tissue (CT) haphazardly formed and arranged
disorganized healing process –> fibrous CT fills the defect in the superficial and deep dermis, new CT lacks adnexa (hair follicles, sweat and sebaceous glands), sometimes fibrous CT becomes granulation tissue (poor tensile strength, wounds can tear or split)
delayed/prevented migration of epithelial cells
when does wound contraction occur
within 6 weeks –> reduced to 5-10% of original size
what prevents or delays wound healing (10)
- infection: single most important cause –> prolonged inflammatory phase
- nutrition: ex. protein deficiency, inhibits collagen synthesis
- mechanical factors: local pressure, trauma or torsion –> wounds may pull apart (dehisce)
- anemia, poor blood supply, low oxygen tension (horse limbs, diabetes)
- age and physcial status
- dehydration (poor perfusion)
- wound fluids (pockets of blood or serum)
- inappropriate dressings (continued use of a debridement dressing during the repair phase)
- foreign bodies (fragments of glass, plant, material, bone)
- underlying neoplasia
what is proud flesh
granulation tissue gone wrong
frequent complication of limb wounds of horses
most common non-neoplastic proliferative cutaneous lesion
continued low level neutrophilic inflammation
protracted fibroblast proliferation
what is the difference in wound healing between horses and ponies
horses –> inflammatory phase weaker and persists
lower initial production of inflammatory mediators
initially inflammation should be stimulated until the wound is filled with granulation tissue
then inflammation should be arrested (but it persists) to reduce the formation of exuberant granulation tissue and facilitate contraction and epithelialization
ponies –> greater contribution of wound contraction (myofibroblasts line up more neatly) epithelialization contributes less due to rapid wound contraction
why do wounds heal more favourably in ponies
inflammatory phase faster and more intense
lower cost of treatment
why do horses form excessive granulation tissue more than ponies
formation of granulation tissue is excessively fast and persists due to the unrelenting inflammatory response
more extensive scar formation because epithelialization is the primary method of wound closure
in ponies –> greater contribution of wound contraction (myofibroblasts line up more neatly) and epithelization contributes less due to rapid wound contraction
what are the features of wound healing in reptiles
similar phases but scar tissue maturation in slow
sutures remain for 4-6 weeks (versus 10 days)
ecdysis (shedding of scales) –> cyclical, days to weeks (activity of epidermis and dermis) promotes healing
after injury hemostasis is achieved by what
fibrin
what are important cells in acute inflammatory phase
macrophages and neutrophils
what are the two important cell types in granulation tissue
- new blood vessels
- fibroblasts
what are the inflammatory cells in tissue repair
- neutrophils (PMN): microbe phagocytosis, macrophage activation, amplify inflammatory response, stimulate repair process. Mediate reactive oxygen species, proteases, TNFa, IL-1B, IL-6, VEGF, IL-8
- macrophage: neutrophil + damaged tissue + micrbobe phagocytosis, amplify repaire response, stimulate angiogenesis and fibroplasia, fibrolysis,. Mediators: TNFa, IL1B, IL-6, PDGF, VEGF, TGFB, tPA uPA (plasminogen activators
- mast cells: control vascular permeability, control influx of PMN, regulate tissue remodelling. Mediators: histamine chymase tryptase
What are the 2 ways angiogenesis can occur and what are the growth factors
- by mobilization of EPC (endothelial pre-cursor cells) from the bone marrow
- from pre-existing vessels
VEGF, (vascular endothelial) bFGF (basic fibroblast)
what is shown here
granulation tissue
blood vessels in verticle plane
fibroblasts in horizontal plane
what is responsible for wound contraction in healing by 2nd intention
presence of myofibroblasts –> modified fibroblasts exhibiting features of contractile smooth muscle cells
