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Wound Healing
Four Phases and Complications
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Wound healing is the body's coordinated response to tissue injury, restoring the skin barrier and limiting blood loss and infection. Medical students study it because the same basic process appears in surgery, trauma care, burns, ulcers, and chronic disease. Healing follows an organized sequence rather than a random repair process. Knowing the phases helps explain why some wounds close normally while others become infected, reopen, or form excessive scar tissue.
The classic four phases are hemostasis, inflammation, proliferation, and remodeling. Platelets first form a clot and release signals, then immune cells clear debris and microbes, fibroblasts and endothelial cells rebuild tissue, and collagen is reorganized over weeks to months. These phases overlap in time, so a wound can show features of more than one phase at once. Complications such as infection, ischemia, diabetes, malnutrition, and repeated mechanical stress can delay or distort healing at any stage.
Key Facts
- Hemostasis begins within minutes: vasoconstriction plus platelet plug formation leads to a fibrin clot.
- Inflammation usually dominates during days 1 to 3, with neutrophils arriving first and macrophages becoming key regulators afterward.
- Proliferation usually occurs from about day 3 to day 21 and includes granulation tissue, angiogenesis, fibroblast activity, and re-epithelialization.
- Remodeling can last weeks to months as type III collagen is gradually replaced and reorganized into stronger collagen bundles.
- Tensile strength of healed skin never returns to 100 percent of uninjured skin and often reaches about 70 to 80 percent maximum.
- Primary intention = wound edges are closely approximated; secondary intention = wound heals by granulation and contraction; tertiary intention = delayed primary closure after initial open management.
Vocabulary
- Hemostasis
- Hemostasis is the immediate process that stops bleeding through vasoconstriction, platelet aggregation, and fibrin clot formation.
- Granulation tissue
- Granulation tissue is new vascular connective tissue made of capillaries, fibroblasts, and extracellular matrix that fills a healing wound.
- Re-epithelialization
- Re-epithelialization is the migration and proliferation of epithelial cells across the wound surface to restore the skin barrier.
- Angiogenesis
- Angiogenesis is the growth of new blood vessels into damaged tissue to supply oxygen and nutrients during repair.
- Wound dehiscence
- Wound dehiscence is partial or complete separation of a previously closed wound because healing is inadequate or stress is excessive.
Common Mistakes to Avoid
- Thinking the four phases happen as isolated blocks, which is wrong because wound healing phases overlap and influence each other continuously.
- Assuming redness always means infection, which is wrong because some erythema and warmth can be normal inflammatory healing findings early on.
- Believing more collagen always means better healing, which is wrong because excessive or disorganized collagen can produce hypertrophic scars or keloids.
- Ignoring systemic factors such as diabetes, poor perfusion, smoking, and malnutrition, which is wrong because local wound care alone cannot fully correct impaired healing biology.
Practice Questions
- 1 A clean surgical incision is closed with sutures immediately after the operation. Name the type of healing intention and identify the wound-healing phase that is most dominant in the first 24 hours.
- 2 A patient has a wound on day 5 after injury. Granulation tissue and new capillary growth are visible. Which phase is dominant, and list two major cellular or tissue events occurring in this phase.
- 3 A patient with diabetes and peripheral arterial disease has a chronic foot ulcer that heals very slowly. Explain how reduced blood supply and metabolic disease interfere with normal wound healing phases.