After an injury, a wound can be classified into three major categories, primary, secondary, and tertiary.
Primary wounds close within hours of the injury.
In secondary wounds, although the wound does not close immediately within hours, there is no formal wound closing time. These wounds close by contraction and reepithelialization.
Tertiary wounds are those that take an extended period to close by suturing or by another mechanism.
Healing an injury is not easy as it seems. A normal wound, after closure, can take up to or maybe even more than a year to fully heal. You can see the change in the appearance of the wound scar over this period quite distinctively.
There are also 3 phases in which a wound heals:
1. Inflammatory phase
2. Proliferative phase
3. Remodeling phase
The first two to four days, starting from the time, of injury, are usually considered as the inflammatory phase of a wound. As the name suggests during this period inflammation and hemostasis is evident. This is due to the collagen exposed to the injury. At the time of wound formation, this collagen initiates intrinsic and extrinsic pathway clotting cascade, resulting in inflammation.
Overlapping the inflammatory phase begins the proliferative phase, which begins around day three. During this phase, a significant cell called the fibroblast is released. These then reach maximum levels by day 7 of the injury. The fibroblast is responsible for three important things during the healing process.
- Collagen formation
The collagen formed during this phase is mainly typed III. This is also the phase where granulation occurs, i.e., a formation of granulation tissue. This is very important to the wound healing process.
The remodeling phase begins when the synthesis and breakdown of collagen are equalized. In this phase, the type III collagen production is discontinued and type I collagen production begins. This is done by the body, till type I: type II ratio becomes 4:1.
In this phase, the fibroblasts morph into myofibroblasts. These result in contraction of tissue. In the meantime, the collagen restructures along tension lines and crosslinks providing more strength, which eventually approaches 80%-85% strength of the normal tissue. The vascularity decreases during this period and a more aesthetically pleasing wound can be seen.
The timelines mentioned are to give a general idea of wound healing phases. Actual timelines of these phases may vary depending upon the nature of the wound.
E.g., for chronic wounds, the inflammatory phase can take much longer as these wounds may have poor perfusion and nutrition or factors that result in the buildup of exudates in the wound. Chronic wounds thus need a much more aggressive approach to treatment during healing than another kind of wounds.
To sum up, wound healing has a complicated and fragile process. When the process of healing wounds goes in the right track, the body works in proper way to heal and replace weaken tissues.