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