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Wound Healing Types and Stages: An Online Review

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Wound Healing Types:

  • Primary Healing
    – Occurring when a wound is closed within a few hours of its creation.
    Wound edges are surgically or mechanically approximated, and collagen
    metabolism provides long-term strength.

  • Delayed Primary
    Healing – Occurs when a poorly delineated wound is left open to protect
    against wound infection. The open wound allows for the natural host
    defense to debride the wound before closure.

  • Secondary Healing
    – Occurs when an open full thickness wound is allowed to close by wound
    contraction and epithelialization.

  • Healing of
    Partial-Thickness Wounds – Occurs when a partial-thickness wound is
    closed primarily by epithelialization. This wound healing involves the
    superficial portion of the dermis. There is minimal collagen deposition,
    and an absence of wound contraction.

Phases Of Wound
Healing:

Coagulation

  • Platelets are
    trapped for essential hemostasis

  • Alpha granules of
    the platelets produce growth factors (PDGF, TGF-b, Platelet factor IV),
    which initiate the wound healing cascade by attracting and activating
    fibroblasts, endothelial cells, and macrophages.

  • Dense bodies of
    the platelets store vasoactive amines (serotonin) which increase vascular
    permeability.

  • Fibrin deriving
    from factor I (Fibrinogen), essential for early wound healing because it
    provides the matrix into which cells can migrate.

Early Inflammation

  • Complement
    activation

  • Infiltration of
    wound with granulocytes (24-48 hours of the injury). This occurs through
    chemotaxis by the release of chemical messengers from platelets. The major
    function of granulocytes is to remove bacteria and foreign debris from the
    wound.

Late Inflammation

  • Appearance of
    monocytes (wound macrophages) (48-72 hours of injury). These cell are
    phagocytic and are the primary producer of the growth factors responsible
    for proliferation of extracellular matrix, smooth muscle, and endothelial
    cells resulting in angiogenisis. These cells occur through chemotaxis by
    attractants such as complements, IgG fragments, collagen, cytokines,
    platelet factor IV, and platelet growth factors (PDGF & TGF-b).

  • Appearance of
    lymphocytes.

Fibroblast
Migration/Collagen Synthesis

  • Stimulated by
    growth factors.

  • Migration of
    mesenchymal cells into the wound.

  • Collagen
    synthesis. Collagen provides strength and integrity for all tissues.

  • Collagen Type
    I
    – structural component of bones, skin, and tendons

  • Collagen Type
    II
    – structural component of cartilage

  • Collagen Type
    III
    – found in association with Type I

  • Collagen Type
    IV
    – structural component of basement membrane

  • Collagen Type
    V
    – found in the cornea.

Angiogenesis

  • Formation of new
    blood vessels. This process is initiated by TGF-b and other growth
    factors, and is ongoing throughout the wound healing phases.

Epithelialization

  • Formation of
    differentiated epithelium which provides a barrier between internal and
    external surroundings.

Remodeling

  • Ongoing collagen
    synthesis and breakdown, remodeling the extracellular matrix.

  • Fibroblast,
    granulocytes, and macrophages produce metalloproteinases which is needed
    for collagen degradation.

  • Metalloproteinases
    inhibitors are produced by TGF-b which underlie the ability to promote
    matrix accumulation.

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