Wound Healing Types and Stages: An Online Review

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.