When tissue injury is extensive or when regenerative capacity is limited, healing occurs by scar formation rather than regeneration. This process restores tissue integrity but not the original function.
Phases of Scar Formation
1. Angiogenesis (Formation of New Blood Vessels)
- Purpose: To supply oxygen and nutrients to the healing tissue.
- Key Growth Factors:
Growth Factor Function VEGF (Vascular Endothelial Growth Factor) Stimulates new blood vessel formation. FGF (Fibroblast Growth Factor family) Promotes endothelial cell proliferation and migration.
2. Formation of Granulation Tissue
- Definition: A soft, pink, granular tissue composed of new capillaries, fibroblasts, and inflammatory cells.
- Main Regulators:
Growth Factor Function PDGF (Platelet-Derived Growth Factor) Recruits fibroblasts and smooth muscle cells. FGF-2 (Fibroblast Growth Factor 2) Promotes fibroblast proliferation and angiogenesis. TGF-β (Transforming Growth Factor Beta) Stimulates fibroblast activation and ECM synthesis.
3. ECM Deposition and Scar Maturation
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Key Mediators:
Mediator Function TGF-β, PDGF, FGF Drive extracellular matrix (ECM) deposition. IL-1, IL-13 Stimulate collagen synthesis, strengthening the scar. -
Outcome: The tissue becomes firm and fibrous, resulting in a collagen-rich scar.
Key Points to Remember
- Scar formation replaces damaged tissue when regeneration is not possible.
- VEGF and FGF promote angiogenesis.
- PDGF, FGF-2, and TGF-β activate fibroblasts and ECM synthesis.
- IL-1 and IL-13 enhance collagen production for scar strength.
- The final scar has high tensile strength but lacks functional tissue.
Learning Objective
By the end of this session, medical students should be able to describe the major steps and molecular mediators involved in scar formation, including angiogenesis, granulation tissue formation, and ECM deposition.
