What are the 3 main phases of wound healing?
- Lag/inflammatory
- Repair
- Remodelling
How long does each phase of wound healing last?
Lag/inflammatory = 1-5 days Repair = 6-16 days Remodelling = from 2-3 weeks to several months
What signs will a wound show during the lag/inflammatory phase?
Classic signs of inflammation: heat, pain, redness, swelling
Describe the lag/inflammatory phase
- Immediate response to injury is haemostasis
- Cells and fluid exit blood vessels and platelets trigger the formation of a fibrin clot
- Neutrophils are attracted to the wound by chemotaxis
- Monocytes enter the wound where they differentiate to macrophages
What are the roles of neutrophils in the lag/inflammatory phase
Degrade necrotic tissue
Control infection by destroying bacteria
What are the roles of macrophages in the lag/inflammatory phase
Remove degenerate neutrophils, necrotic tissue and debris by phagocytosis
Secrete growth factors that regulate wound healing
What are the 3 components of the repair phase?
- connective tissue repair
- wound contraction
- epithelialisation
Describe the processes involved in connective tissue repair
- mesenchymal cells in the wound edges differentiate into fibroblasts
- fibroblasts create a new collagenous extracellular matrix
- capillary growth follows fibroblast migration: combination forms granulation tissue
How does granulation tissue become a paler scar?
By day 7-14 after injury the collagen content of the wound stabilises, fibroblasts undergo apoptosis and the new capillaries undergo apoptosis resulting in acellular tissue
Describe the process of wound contraction
- specialised myofibroblasts proliferate the wound and attach to the matrix and contract
- contraction continues until the wound edges meet and contact inhibition occurs
Describe the process of epithelialisation
- Epithelial cells from the wound edges and any remaining hair follicles migrate across the wound to form a monolayer
- Proliferation occurs to increase thickness
How does epithelialisation differ in partial thickness and full thickness wounds?
Partial: begins immediately
Full: requires an adequate granulation bed so begins 4-5 days post injury
Describe the remodelling phase
- The collagen content and strength of the wound increase rapidly over the first 14-16 days
- After this the cellular content of the granulation tissue reduces and collagen bundles reorganise by thickening, cross-linking and reorienting across lines of tension
Give examples of local factors affecting wound healing
- Wound perfusion
- Tissue viability
- Wound fluid accumulation
- Infection
- Pressure, motion, tension
Give examples of systemic factors affecting wound healing
- immunosuppression: disease (FIV, hyperadrenocorticism), glucocorticoid administration
- neoplasia: residual disease, cytotoxic drugs
What are the 4 classifications of wounds?
- Clean
- Clean-contaminated
- Contaminated
- Dirty
Describe a clean wound
Elective surgical wounds not entering the respiratory, urogenital or GI tracts with no break in asepsis
Describe a clean-contaminated wound
Elective surgical wounds entering the respiratory, urogenital or GI tracts without significant contamination or minor breaks in asepsis
Describe a contaminated wound
- Fresh traumatic wounds less than 4-6 hours old
- surgical wounds entering the respiratory, urogenital or GI tracts
- significant contamination
- surgery in the presence of inflammation
- major break in asepsis
Describe a dirty wound
- traumatic wounds greater then 4-6 hours old
- traumatic wounds contaminated with foreign material
- perforation of a hollow viscus
- surgery in the presence of an abscess
Define the following:
- Abrasion
- Avulsion
- Laceration
- a partial thickness wound with loss of epidermis and part of dermis
- tearing of tissue from its attachments
- sharp trauma resulting in an irregular wound with tearing of tissue and trauma of underlying tissue.
What are the possible causes of burns?
Hot things
Very cold things
Electricity
Chemicals
How does the intestine specifically respond to wound healing, what factors are critical to the success of healing?
- In the first 1-2 days after injury collagenase activity in the wound causes a reduction in wound strength: this effect is increased in sepsis
- Avoid infection
- Preserve blood supply
- Avoid tension
How do peripheral nerves respond when they are injured?
When a nerve is cut the severed ends retract, the cell body swells, the nucleus become eccentrically placed and the axon undergoes degeneration
