Skin Wound Healing 2
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What are the three overlapping stages of wound healing?
- Formation of granulation tissue in the dermis - angiogenesis and migration and proliferation of fibroblasts
- Fibroblasts deposit ECM and then remodel it to form a scar
What are the two different types of angiogenesis?
- Angiogenesis by mobilisation of endothelial precursor cells from the bone marrow
- Angiogenesis from pre-existing vessels
When does granulation tissue form?
What term is often used to describe exuberant granulation tissue in horses?
What should healthy granulation tissue look like?
It should have a soft appearance and be a salmon pink colour
Describe the appearance of granulation tissue on histology
Blood vessels and fibroblasts are arranged perpendicular to each other.
What stimulates fibroblast migration and ECM deposition?
What growth factor is important for angiogenesis?
Vascular endothelial growth factor (VEGF)
What happens to tissue as healing continues and scar formation begins?
The number of proliferating fibroblasts and blood vessels decreases.
Give a brief overview of wound healing, with all the steps involved
- Tissue injury - cells become damaged
- Inflammation - immediately there is inflammation. Neutrophils come in through dilation of vessels and chemotaxis. Start initial clean up of wound.
- Formation of granulation tissue - capillary sprouts develop and the bone marrow produces endothelial precursor cells to make new endothelial blood vessels. Fibroblasts produce collagen.
- Scar formation - blood vessels regress and fibroblasts become thinner
In what situation would healing by first/second intention occur? a) In a clean, uninfected surgical incision closed with sutures b) In a large abscess
- a) Healing by first intention
- b) Healing by second intention
In healing by first intention there is focal/widespread disruption of epithelial basement membrane, death of small/large numbers of epithelial and connective tissue cells? Which is more predominant: epithelial regeneration or fibrosis?
Focal, small, epithelial regeneration
Describe what happens during healing by first intention at a) 24hrs to 7days b) early weeks c) months to a year
- a) Neutrophils migrate into fibrin clot, followed by macrophages. Basal cells at the cut edge of the epidermis begin to show mitotic activity. Epithelial cells start to migrate and proliferate across the dermis. Fibroblasts migrate in.
- b) Continued collagen accumulation. Fibroblasts start to reduce in number. Decreased leukocytes, oedema and vascular permeability. 'Blanching'. Few to no inflammatory cells. Epidermis should be intact at 10 days.
- c) Scar forms (dense connective tissue covered by essentially normal epidermis). Dermal appendages that were destroyed e.g. hair follicles are permanently lost
Describe what happens during healing by second intention.
- Blood clot
- Necrotic slough
- Acute inflammation
- Phase of rapid proliferation of granulation tissue 1-2 weeks
- Granulation tissue maturation and wound contraction at 3-6 weeks - epithelial proliferation across granulation tissue surface before gradually shedding scab, granulation tissue begins to contract pulling wound edges closer together
- Larger fibrous scar - pale depressed scar with surrounding puckering caused by wound contraction, thin epidermis over scar, white scar devoid of appendages
What causes wound contraction?
Myofibroblasts - modified fibroblasts exhibiting features of smooth muscle cels
Which animal heals more favourably: horses or ponies?
How does the inflammatory phase in horses affect their wound healing?
The inflammatory phase is weaker and persists for longer in horses. This means formulation of granulation tissue persists due to the unrelenting inflammatory response.
What prevents or delays wound healing?
- Mechanical factors
- Anaemia, blood supply, oxygen tension
- Age and physical status
- Wound fluids
- Inappropriate dressings
- Foreign bodies
- Underlying neoplasia
How do you manage proud flesh?
Keep cutting it back
How long do sutures remain in in reptiles vs mammals? Why?
3-4 weeks in reptiles vs 10 days in mammals. This is because scar tissue maturation is slow in reptiles.
What is the term used to describe shedding of skin/scales?
How can we promote healing in reptiles?
By maintaining them at the upper end of their optimal environmental temperature range
True or false: wounds orientated cranial to caudal heal more quickly than transverse wounds in reptiles?
True or false: in reptiles open wounds e.g. lamp burns have a relatively high incidence of secondary infection?
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