Wound healing
Related Subjects:
|Acute Inflammation
|Chronic Inflammation
|Wound healing and Repair
🩹 About Wound Healing and Repair
- Wound healing is a complex biological process restoring the integrity of skin, bone, and organs after injury.
- Healing may occur by Primary Intention (clean, sutured wounds) or Secondary Intention (open, contaminated or large tissue loss wounds).
- Other tissues (bone 🦴, brain 🧠, liver, GI tract) have unique repair mechanisms.
✂️ Primary Intention Healing
- Seen in clean surgical incisions or tidy lacerations where wound edges are closely apposed with sutures or staples.
- Haemostasis: Platelets + clotting cascade form a fibrin-rich clot, preventing infection and sealing the wound.
- Inflammation: Neutrophils → macrophages clear debris, while cytokines recruit fibroblasts.
- Proliferation: Fibroblasts lay down type III collagen; angiogenesis forms granulation tissue.
- Remodelling: Collagen matures into type I → tensile strength ↑, scar forms.
- Clinical Pearl: Fastest healing, minimal scarring. Used in appendectomy or C-section wounds.
🕳️ Secondary Intention Healing
- Occurs when wound edges cannot be approximated (e.g. large traumatic wounds, pressure ulcers).
- More granulation tissue, slower epithelialisation, more contraction → larger scar.
- Higher risk of infection and functional impairment.
- Clinical Example: Large leg ulcer post-trauma healing slowly by granulation.
🧬 General Phases of Healing
- Vascular Response: Vasoconstriction → vasodilation → ↑ permeability.
- Inflammation: Neutrophils, macrophages clear necrotic tissue & pathogens.
- Proliferation: Fibroblasts (collagen), angiogenesis 🌱, epithelial cell migration.
- Remodelling: Collagen cross-linking, scar contraction, ↑ tensile strength (never reaches 100% of original tissue strength).
- Modifiers: Diabetes, poor nutrition, infection, steroids, and old age ⏳ slow healing.
🦴 Bone Healing
- Haematoma (hours–days): Clot + inflammatory cells form.
- Inflammation (days): Macrophages/neutrophils clear necrotic bone.
- Repair (weeks): Soft callus (cartilage + collagen) → hard callus (woven bone).
- Remodelling (months–years): Woven bone → lamellar bone via osteoclast/osteoblast balance, aligned to mechanical stress (Wolff’s law).
- Clinical Note: Delayed union in smokers 🚬, diabetics, or if poor blood supply.
🧠 Brain Healing
- No true regeneration of neurons – instead astrocytes form a glial scar.
- Neuroinflammation + microglia clear debris; neurogenesis limited to hippocampus.
- Clinical: Functional recovery relies on plasticity + rehabilitation rather than tissue replacement.
- Complications: seizures, cognitive decline, post-stroke disability.
🫀 Healing in Other Organs
- Liver: Hepatocytes can regenerate 🧬 → reconstitute mass unless fibrosis/cirrhosis develops.
- Skin: Rapid epithelialisation; infection control & moisture balance critical for healing.
- GI Tract: Rapid epithelial turnover; chronic inflammation (e.g. Crohn’s, UC) disrupts healing.
✅ Conclusion
- Healing is tissue-specific but follows broad phases: haemostasis → inflammation → proliferation → remodelling.
- Clinical management must consider systemic factors (nutrition, comorbidities) and local factors (infection, vascularity).
- Primary vs secondary intention distinction is key for surgical decision-making and exam answers.
