Tissue Repair

Tissue Repair

Tissue repair is the restoration of tissue structure and function following injury. This process overlaps with the inflammatory response and can occur in two forms: tissue regeneration, which involves the replacement of injured parenchymal cells with similar cells, and tissue replacement (fibrous tissue repair), which results in scar formation or fibrosis.

Types of Body Tissues and Organs

There are two main types of body tissues: parenchymal tissues, containing functioning cells (e.g., hepatocytes), and stromal tissues, which include supportive connective tissues, blood vessels, and the extracellular matrix. The extracellular matrix itself is the interstitial matrix found within blood and tissue cells.

Wound Healing: Intention Types

Wound healing can occur in three different intentions: primary intentions, which pertain to small, clean wounds; secondary intentions, associated with large wounds that have tissue loss and potential contamination; and tertiary intention, which is a delayed primary approach where the wound is intentionally left open to prevent contamination.

Phases of Healing by Primary Intention

The healing process for primary intentions consists of three phases. The first is the inflammatory phase, lasting approximately 3-5 days, which includes clotting and the approximation of wound edges. This is followed by the proliferative phase, lasting from 5 days to 4 weeks, during which fibroblasts migrate, collagen is secreted, and new capillary formation occurs. Finally, the maturation phase, also known as remodeling, takes place over several weeks to months, focusing on the remodeling of collagen and the strengthening of the scar.

Inflammatory Phase Details

During the inflammatory phase, hemostasis is achieved through blood vessel constriction and clot formation. The cellular response is initiated by neutrophils, which are the first responders, followed by macrophages that help clear debris and release growth factors.

Proliferative Phase Details

The proliferative phase is characterized by the formation of granulation tissue, which is a glistening red, moist tissue rich in capillaries and fibroblasts. Epithelization occurs as epithelial cells migrate and proliferate, sealing the wounds quickly in cases of primary intentions. However, excessive granulation tissue, known as proud flesh, may prevent re-epithelization and might necessitate removal.

Remodeling Phase Details

The remodeling phase begins approximately three weeks post-injury and can last for months, during which continuous remodeling occurs in the scar tissue, leading to an increase in collagen strength. It is important to note that most wounds do not regain their full tensile strength post-healing.

Keloids

Keloids are an abnormal form of scar formation that results from excessive tissue production, and they are more likely to occur in individuals who are genetically predisposed.