4.1. Physiology of Healing: Phases of Healing

Healing is a complex process that involves a series of biochemical and cellular events that aim to restore tissue integrity after injury. This process is divided into three main phases: inflammatory, proliferative and maturation or remodeling. Each phase has specific characteristics and is crucial for effective wound healing.

Inflammatory Phase

The inflammatory phase is the first step in the healing process. It starts immediately after the injury and can last up to three days. During this phase, vasoconstriction occurs to minimize blood loss. This is followed by the release of various chemicals, such as histamine and bradykinin, which cause vasodilation and increased vascular permeability, allowing immune cells, nutrients and growth factors to reach the site of injury.

Immune cells, such as neutrophils and macrophages, play a crucial role in this phase. Neutrophils are the first cells to arrive at the site of injury and begin to phagocytose bacteria and cell debris. Macrophages arrive a little later and continue the work of neutrophils. They also release growth factors that are essential for the next phase of healing.

Proliferative Phase

The proliferative phase begins around the third day and can last up to three weeks. This phase is characterized by the formation of new tissue and blood vessels, as well as wound contraction. Fibroblasts, which are attracted to the site of injury by growth factors released by macrophages, play a crucial role at this stage. They produce collagen, which is the main protein of the extracellular matrix and is crucial for the strength and integrity of new tissue.

The new blood vessels, which are formed during the process of angiogenesis, supply oxygen and nutrients to the new tissue. Wound contraction is facilitated by myofibroblastic cells, which resemble both fibroblasts and smooth muscle cells. They contract and pull the edges of the wound together, thus reducing the size of the wound.

Maturation or Remodeling Phase

The maturation or remodeling phase is the last phase of healing and can last from several weeks to two years. During this phase, collagen is remodeled and reorganized, and excess cells and blood vessels are removed by apoptosis, or programmed cell death. This results in scar tissue that is stronger and more like normal tissue.

However, it is important to note that scar tissue is never as strong as the original tissue. For example, scarred skin only has about 80% of the strength of normal skin. In addition, scar appearance can vary depending on a number of factors, including the location and type of wound, the individual's age and general health, and care of the wound during the healing process.

In summary, wound healing is a complex process involving multiple phases and a variety of cells and biochemical factors. A clear understanding of this process is crucial for effectively treating wounds and preventing complications such as excessive scarring or inadequate healing.

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