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Path - Healing + Repair (ii) (Pathological wound healing (excess scarring,…
Path - Healing + Repair (ii)
Phases of wound healing
Inflamm phase
acute, after initial injury
haemotoma formation, infiltration by neutrophils + macrophages
Prolif phase
epidermal prolif (regrowth), dermal repair
granulation tissue (angiogenesis, fibroblast prolif, synthesis of ECM proteins)
remodelling phase
granulation tissue replaced by fibrous tissue
remodelling of parenchymal cells to restore function + elasticity
remodelling of connective tissue to achieve strength
excess ECM degraded by metalloproteinase
Types of Wound healing
primary intention
no infection, well-approximated closed edges (e.g. surgery)
day 1: haematoma, acute inflamm, epithelial prolif, neutrophil infiltration
day 2: macrophage infiltration, epithelial cells cover wound surface
day 3: granulation tissue
day 5: collagen deposition
day 7: sutures removed
Walker's law: sutures removed @ 1 wk, strength = 10% of normal skin, @ 3/4months = 80% (will never return to 100%)
secondary intention
infection, ulcer, abscess
extensive cell loss, gaping wound
similar to primary but slower + more intense inflamm reaction
edges not approximated so granulation tissue fills gap
wound contraction via myofibroblasts - more scarring
Pathological wound healing
deficient scar formation - rupture
excess scarring
e.g. keloid - excess type 3 collagen, genetic predisposition, more common in Africans
contracture deformity (connective tissue stiffness/constriction)
v rarely malignant transformation
on mucosal surfaces (labile cells)
erosion healed by regeneration
ulceration healed by regeneration + fibrosis
on liver (hepatocytes = stable)
single short-lived injury healed by regernation (e.g. hep A as it affects hepatocytes only)
chronic injury heals by cirrhosis (fibrosis) - e.g. hep B + C as they affect stroma also