A wound or injury can occur to anyone anytime. The wound can be acute or chronic and depending on the intensity of damage done to the blood vessels underneath, wound takes time for healing. Any type of chronic wound undergoes the following 4 phases for complete healing.
The healing of wound is divided into 4 stages as below :
Hemostasis :
Hemostasis phase is the first step of the natural response of the body to the wound. The blood vessels in the wound get shrunk forming blood clot. The wounded blood vessels have to be sealed just like the utility workers seal the gas pipes and water lines, once the house got damaged due to flood. This process is called haemostasis and this is followed by dilation of blood vessels which eventually relaxes. The blood platelets begin to secrete vasoconstrictive particles to help in the process of sealing the blood vessel. The defense mechanism of the body springs into action sending lots of enzymes, growth factors and nutrients to the wounded area.
Slowly the platelets collect together and move towards the exposed collagen by name Adenosine diphosphate. In this process they would interact with each other thus triggering intrinsic clotting by the release of thrombin, which eventually produces fibrin. This fibrin forms a mesh or net which strengthens the platelets forming stable hemostatic zone. Now, it is the turn of platelets which produce cytokines which is one of the essential factors for subsequent process. This stage is called hemostasis and all the above steps occurs within minutes of initial wound.
Inflammation Phase :
This is the second stage in the process of wound healing. This stage will lasts for 4 days after injury. Neutrophils are responsible for removing the debris and microorganisms and thus are involved in cleaning the wound. Local mast cells help the neutrophils in this cleaning process. During this process, fibrin gets broken down and it is the macrophages are particles that direct the defense mechanism of wound healing process. Macrophages are effective in removing the bacteria thus aiding in defense. They also discharge various growth factors like fibroblast growth factor and epidermal growth factor thus repairing the wounded skin and taking it to the next stage.
Proliferative Phase :
It is also called as granulation and contraction stage which lasts anywhere from 4-20 days after injury. If the size of the wound is large it may take even long time for proliferation. Fibroblasts start producing collagen fibers for repairing the wounds upon which dermal regeneration takes place. This process involves replacement of dermis layer of the skin and sub-dermal tissues in case of deeper wounds. Special layers of fibroblasts are involved for wound contraction. It is time for the pericytes to regenerate the outer layers of blood vessels and endothelial cells starts giving the inner lining for capillaries. This process that involves forming new lining is called angiogenesis. Epithelization takes place by keratinocytes and after the completion of this task, they separate to form the outer protective layer called stratum corneum.
Maturation Phase :
Once the task of remodeling of dermal tissues is complete, fibroblasts will start the work of strengthening the cells. It builds up strength for the wounded cells. This phase of remodeling or maturation can take up to 2 years or even more depending on the size and intensity of wound. Fibroblasts will repeatedly carry out this task of remodeling the cells. Since this stage of building up strength lasts for long time, any minor injury on the healing wounds will cause them to break down easily. In this stage, collagen particles are transformed from type III to type I. There will be more of cellular activity and number of blood vessels found in the wounded area will gradually reduce.