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Phases of Wound Healing


What is a Wound?

 A wound is a break in the flow of soft body structure and occurs due to violence or trauma to tissues. Wound is of two types. One is acute wound and the other is chronic wound.  

The goal of wound healing:

The prime motive of the healing process is to fill the gap which was conceived by tissue destruction. Along with that role, there is another role of this process and that is to restore the structural continuity of the injured part. 

Wound Healing Process:

The process of wound healing is a complex sequence of events. It starts immediately after the injury and wraps up with the complete closure of the wound. The cells undergo a number of complicated biological changes in this continuous process. 

Why do cells go through the changes?

The cells go through changes to:

  • Facilitate Hemostasis
  • Combat Infection
  • Migrate into the wound space
  • Form new blood vessels
  • Shrink to close the defect
  • Remodeling
What are the phases of wound healing?

The phases of wound healing are:

  • Hemostasis
  • Inflammatory phase
  • Proliferation phase
  • Maturation phase.
These all phases remain distinct in terms of time after the injury which means that inflammation will not occur before the hemostasis.

Hemostasis: 
Hemostasis is a mechanism for controlling the bleed. It starts right after the injury. In the first part, constriction occurs in blood vessels to stop the blood flow. And then platelets start aggregating to make the bond with the sub-endothelial surface of the broken blood vessel's epithelial wall. Then fibrin strands start joining within 60 seconds. After the beginning of fibrin mesh, the conversion of blood from a liquid to gel occurs with the help of pro-coagulants and prothrombin releasing. Thrombus formation or clotting holds the platelets and blood cells confined in the wound region. The blood also becomes more viscous so clotting can easily occur.

Inflammatory Phase:
The main object of inflammation is to detach the microorganism or foreign debris. The inflammatory phase also limits the extent of tissue damage and prepares the environment for wound healing. The inflammation is manifested by:
  • Pain'
  • Heat
  • Redness
  • Swelling
  • Loss of function. 
How the inflammation process occurs?

The inflammation starts with dilation of arterioles and venules nearby the injured area. The permeability of capillary increases that makes easy for the fluid to move into the affected tissue. 

Phagocytosis: Phago means to eat and cytisis means cells. Phagocytosis is the process of engulfing bacteria and cellular debris. The most important phagocytes are:
  • Leukocytes or WBCs 
  • Neutrophils 
  • Macrophages
Proliferation Phase: 
Proliferation means the rapid and repeated reproduction of new parts via cell division. So in proliferation phase, the formation of new tissue are formed to fill the gap. Fibroblasts play an important role in proliferation phase which appear in large quantity within three days of injury. Fibroblasts are connective tissue cells that synthesize and secrete collagen, elastin, and reticular fibers. Fibroblasts also secrete growth factor which induce the growth of blood vessels through angiogenesis. 
Granulation tissues is a fibrous connective tissue that replaces fibron clot in healing the wound. Granulation tissue contain newly developed blood vessels and fills the wound bed. The next stage of proliferation phase is epithelialization. In epithelialization, marginal basal cells lose their adhesion, and migrate across the wound area in train fashion. The final stage is wound contraction in which wound size is decreased. At the end of proliferation, the WBCs leave the wound site. 

Maturation Phase: 
Maturation phase starts in 1 to 3 weeks and may lasts between 6 months to 12 years. The scar tissues are formed in maturation phase due to simultaneous synthesis and lyses of collagen. 70 to 80% strength increase in the scar tissue. There is a remodeling stage in maturation phase. 

What are the factors that affect wound healing? 

The factors which affect wound healing are:
  1. Nutrition
  2. Age
  3. Disease
  4. Vascularity
  5. Medications
What are the medications that affect wound healing?

Steroids: When vitamin  A is applied topically, it can reverse the negative effect of steroid which means that inflammation phase will be restart.  

NSAIDs: NSAIDs reduce the synthesis of collage so the strength is also reduced. NSAIDs inhibit the inflammatory response as well as increase of infection. 

What is mean by delayed healing?

Sometimes the wound healing process is stuck in the inflammatory phase and this is the delayed healing. It results in chronic wounds. 


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