PA4.1 | Healing & Repair — Regeneration, Granulation Tissue, Wound Healing — Summary & Reflection

REFLECT

Spend 3-4 minutes answering these before you proceed:

1. A burn patient has a large wound on the dorsum of the hand that has healed spontaneously by secondary intention over 6 weeks. The hand is now flexed at the MCP joints and cannot be fully extended. Which process caused this, and at the cellular/molecular level, what drove it?

1. A patient who received prolonged steroid therapy for rheumatoid arthritis undergoes an elective cholecystectomy. Name three specific reasons why wound healing may be impaired in this patient.

1. You are examining a healing wound on day 12. It appears pink, moist, slightly raised, and bleeds on gentle touch. Is this expected? What tissue are you observing, and what phase of healing does this represent?

KEY TAKEAWAYS

Core take-aways from this SDL:

• Two outcomes after injury: regeneration (identical cells, intact framework required) vs repair by connective tissue (scar). Cell class determines which is possible: labile > stable > permanent.

• Repair proceeds in four steps: haemostasis → granulation tissue (angiogenesis + fibroblast proliferation + ECM) → proliferation → maturation/remodelling (type III → type I collagen via MMPs, tensile strength plateau at ~70-80%).

• Key growth factors: VEGF (angiogenesis), PDGF (fibroblast recruitment), FGF (angiogenesis + proliferation), TGF-β (collagen synthesis, master fibrogenic signal).

• Primary vs secondary intention: primary = apposed wound, minimal scar; secondary = large defect, abundant granulation tissue, wound contraction by myofibroblasts, larger scar.

• Factors impairing healing: infection (most important locally), ischaemia, vitamin C/protein/zinc deficiency, diabetes, corticosteroids, age.

• Complications: dehiscence/ulceration (under-healing); hypertrophic scar (within margin, regresses) vs keloid (beyond margin, does not regress, recurs); contracture.

• Other tissues: bone — can truly regenerate if immobilised and framework intact; liver — regenerates with intact reticulin, scars if framework destroyed; CNS — permanent cells, defects filled by gliosis (astrocyte scar).