Pathology Cheat Sheet
Build the Repair Bed
Connective tissue repair for NEET-PG: haemostasis, granulation tissue, PDGF, VEGF angiogenesis, TGF-beta fibrosis, MMPs, and the scar remodelling phases.
MedNext Academy | 3 min read
Build the Repair Bed
Connective tissue repair for NEET-PG: haemostasis, granulation tissue, PDGF, VEGF angiogenesis, TGF-beta fibrosis, MMPs, and the scar remodelling phases.
The ordered but overlapping steps of connective tissue repair, from haemostasis through granulation tissue to scar remodelling.
High-yield lines
- Repair begins with haemostasis and a provisional fibrin-fibronectin matrix that also stores growth factors.
- Platelet alpha granules release platelet-derived growth factor and transforming growth factor beta as the first repair signals.
- Neutrophils dominate the early inflammatory phase, and macrophages take over from around day three to orchestrate repair.
- Granulation tissue appears within days and contains new capillaries, fibroblasts, and loose matrix, giving a soft pink granular surface.
- Vascular endothelial growth factor is the central driver of angiogenesis in granulation tissue and is induced by hypoxia through HIF-1 alpha.
- Platelet-derived growth factor recruits and proliferates fibroblasts and smooth muscle cells.
- Transforming growth factor beta is the most potent profibrotic cytokine, stimulating collagen synthesis and inhibiting matrix degradation.
- Fibroblasts synthesise collagen, and some become contractile myofibroblasts that contract the wound.
- Matrix metalloproteinases are zinc-dependent enzymes that remodel the extracellular matrix and are restrained by tissue inhibitors.
- Scar maturation involves replacement of type III collagen by type I, reorientation along stress lines, and regression of vessels.
- Hepatic stellate (Ito) cells are the liver equivalent of myofibroblasts and drive fibrosis leading to cirrhosis.
- An imbalance favouring matrix metalloproteinases produces chronic non-healing ulcers, while excess inhibition promotes fibrosis.
Mapped competency codes
- PA5.1
Continue into the full chapter
This summary maps to PA5-healing-and-repair.
Frequently Asked Questions
What are the components of granulation tissue?
New capillaries from angiogenesis, proliferating fibroblasts, and a loose extracellular matrix, giving a soft pink granular appearance.
Which growth factor drives angiogenesis in wound repair?
Vascular endothelial growth factor, which is induced by hypoxia through HIF-1 alpha and stimulates endothelial proliferation and migration.
Which cytokine is the master regulator of fibrosis?
Transforming growth factor beta, which stimulates fibroblast collagen production, promotes myofibroblast differentiation, and inhibits matrix degradation.
What controls extracellular matrix remodelling in a healing wound?
The balance between matrix metalloproteinases, which degrade matrix, and their tissue inhibitors, which restrain that degradation.
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