Wound Healing

A. Regeneration

Following injury, the skin has a tremendous capacity to heal. When the injury involves disruption of the dermis, post-natal wounds heal with a macrophage-effected (8,9) fibro-proliferative repair process which results in the laying down of a new collagen-rich dermal matrix over which epidermal continuity can be reestablished. This process of repair and the subsequent reorganization of the dermal matrix results in scar formation.

A scar is produced as the result of a reorganization of mesenchymal tissue produced in response to the healing of a wound. A wound is the discontinuity in tissue integrity. Such a discontinuity may be physical, as in a surgical incision, or functional, as in a dermal burn. A complex pathophysiological response results in a cascade of cell-matrix interactions that comprise the biological concept of wound healing. Such healing, as occurs in the post-natal human occurs by two major processes regeneration and repair (Fig. 1). Regeneration is illustrated by the rapid healing of a superficial abrasion of the skin. Complete replacement of the lost tissue occurs rapidly and following a period of hyperaemia and/or hypopigmentation the skin will return to its pre-injured appearance and function. Regeneration has occurred with a replacement of the lost tissue by an identical new tissue.

B. Repair

Repair is very different. Repair occurs when the wound involves mesenchymal connective tissue. The predominant matrix component of connective tissue is collagen and the major cell type is the fibroblast. Skin, the largest organ in the body, is composed of both ectodermally and mesodermally derived layers. The dermis is derived from the mesoderm and when the dermis is damaged it will attempt to heal by the process of repair. The outcome of repair is scar tissue. This is obvious in the skin and produces both deformity and disability. Scarring does, however, have widespread effects throughout the body resulting in an extensive range of morbidity. Connective tissues, which produce the scaffolding for specialized organ tissues, can be deformed and distorted by the process of scarring and can result in respiratory dysfunction due to lung parenchymal fibrosis, liver dysfunction due to cirrhosis, renal dysfunction due to post-glomerulonephritic scarring, adhesions in the bowel after surgery, strictures resulting in infertility after pelvic inflammatory disease affecting the fallopian tubes, urinary dysfunction following urinary tract strictures, post-traumatic

TISSUE

INJURY

WOUND

'A discontinuity in tissue integrity' (functional and/or structural)

HEALING

'Restoring tissue integrity' (functional and/or structural)

REGENERATION

NO SCAR

REPAIR

SCAR

Figure 1 The key difference between regeneration and repair: scar or no scar.

epilepsy, vascular compromise due to vessel narrowing secondary to atherosclerotic disease. The extent of human pathology and disease associated with scarring is vast. As such, the study of wound healing and the research into the fundamental biological processes of scarring is of major interest throughout the globe. It is evident that research in wound healing and scarring is not carried out in isolation as the biological phenomenon of repair and regeneration have to be closely related to tissue development as well as degeneration and ageing.

C. Fetal

Fetal wounds heal without scarring (10-17). The mechanism for the scarless healing in the fetus is unclear; immuno-histochemical staining (18) and biochemical studies (19) indicate that there is a deposition of a collagen-rich repair matrix, which is rapidly organized. In an early-third trimester fetal sheep, there is no observable scar tissue by 2 weeks after wounding. What is notable is that while macrophages are present in these fetal wounds, polymorphonuclear leucocytes (PML) are not. Healing after the mid-third trimester in fetal sheep, is associated with scarring and this time point coincides with the appearance of PMLs in the circulation (10). It appears that earlier fetal wounds have an ability to undertake an autonomous, site-specific repair while classically activated macrophage-effected repair is not site-specific and ends in scarring.

How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

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