Wound Healing Flashcards
The hypodermis (subcutis) lies below the dermis and is also known as the_____.
Superficial fascia
Direct cutaneous vessels run ____ to the skin, and contain perpendicular branches, that form three layers starting from bottom up:
- Parallel to the skin
- Deep/subdermal plexus
- Cutaneous/Middle of plexus
- Subpapillary/Superficial plexus
Within the subdermal plexus, list areas where the panniculus muscle is present and where it is absent.
- Panniculus present
- Trunk, neck
- Must undermine fascial plane beneath muscle
- Panniculus absent
- Extremities, part of the head
- Undermine under deep surface of the dermis
Phases of wound healing
- Inflammation
- Hemorrhage, clotting, cellular influx via growth factors and cytokines, debridement
- Repair (proliferative)
- Granulation, contraction, epithelialization
- Maturation
Neutrophils -
- When do they arive?
- Are they essential for healing?
- Their function?
- Arrive in about 6 hours
- NOT essential for healing
- Stay for 2-3 days
- Phagocytize bacteria and debris
- Proteolytic enzymes
- O2-radicles
- Monocyte stimulation
Do you need bacteria for pus formation?
No, pus is dead neutrophils, degraded tissue, and wound fluid, with or without bacteria.
Macrophages
- When do they arrive?
- Are they essential for wound healing?
- Functions?
- Arrive in about 12 hours
- ESSENTIAL for wound healing
- Drawn by endotoxins, collagen fragments
- Phagocytosis of large particles
- Produce cytokines that potentiate immune response
- Produce growth factors for cellular proliferation, INCLUDING FIBROBLASTS
- Recruit mesenchymal cells, stimulate angiogenesis, and modulate wound matrix
Lymphocytes
Arrival, function
- Arrive after neutrophils and macrophages
- Not essential for wound healing
- Modulate migration and protein syntehsis of other cells
Repair phase
When does it begin? How long does it last? Characterized by:
- Begins at days 3-5
- Lasts 2-3 weeks
- Characterized by:
- Angiogensis
- Fibroplasia
- Contraction
- Epithelialization
Granulation tissue =
Fibroblasts + new capillaries
Angiogenesis
- New capillaries form from migration and proliferation of endothelial cells
- response to growth facotrs produced by macrophages
- Regulated by proteins in extracellular matrix
Fibroplasia
- Proliferation of fibroblasts and production of collagen
- Fibroblasts migration influenced by growth factors and integrin receptors in extracellular matrix
- Collagen type III replaced by type I as fibroblasts fill the wound
- Greatest increase in collagen content occurs 7-14 days after wounding
- Then slow gian in stregnth over several months
Granulation Tissue
- Follow fibroblasts along collagen strands
- Capillary buds from existing vessel –> unite with other buds or damaged vessels
- Bring oxygen and nutrients to the wound
- Remove waste
- Appears at days 3-5 and formed at a rate of 0.4 to 1 mm/day
- Fills defect
- Barrier to infection
- Surface for epithelialization and source of myofibroblasts (reason why wound can contract)
- Should be redish/pink - like a watermelon color
Wound Contraction
- Process that decreases the size of a wound
- Migration of myofibroblasts towards center
- Centripital force on wound edges
- Ceases when surrounding skin equals contracting forces. Can stop with inadequate myofibroblasts.
- Inhibited or delayed by corticosteroids, some chemotherapy drugs, smooth muscle relaxants
Is wound contraction dependent of epithelialization?
No, wound contraction is independent of epithelialization, but often concurrent.
Excessive contraction leads to ____
Contracture - this is bad, happens frequently with tubular structures and pieraritcular wounds.
Epithelialization
- Barrier to infection and fluid loss
- Mobilization –> proliferation –> differentiation
- From wound edge and appendages
- Begins at 24 to 48 horus in sutured wounds
- Begins when adquate granulation appears in open wounds (4-5 days)
- Begins immediately in parital-thickness wounds
In epithelialization, migration is guided by ____
Collagen fibers
In epithelialization, epithelial cells migrate until in contact with ____. This process is called _____
other epithelial cells; contact inhibition
Epithelialization is faster in ___ wound than ___ wound.
Faster in moist than dry
Maturation Phase
- Scar gains strength
- Most rapid at 7-14 days
- 20% at 3 weeks
- 80% maximum (except urinary bladder and bone that go back to 100% strength)
- Begins with adequate collagen (17-20 days)
- Continues for years
- Collagen cross-links - ones that are lined appropriately survive
- Capillaries decrease
Wound healing - cats vs dogs
- Cat sutured wound is weaker than dog at one week
- Cats heal slower by second intention, with less granulation and more contraction
Will granulation tissue grow over bone or nerves?
NO! - intact surfaces do not support granulation
Topical Antibiotics for Wound treatment
- Apply within 1-3 hours
- Benefits must outweigh cytotoxic effect
- Solutions or creams perferable
- Ointments - slow, may promote bacteria
- Powders - irritating
Systemic antibiotics in woudn treatment
- Used to treat infection, NOT as a preventative
- do NOT use anitbiotics as excuse for closing infectd wound - does not prevent suppuration
