The Role of Wound Contraction in Dermal Repair

The Scar Solution Natural Scar Removal

The Scar Solution By Sean Lowry

Get Instant Access

In mammals that have loose skins, closure of exci-sional skin wounds is aided by contraction of the dermis

FIGURE 2.5 Diagram illustrating contraction of the skin in rodent (A) vs human (B) circular excisional wounds. Outer circle = initial perimeter of the wound. Inner circle = position to which the skin is drawn by contraction. Arrows indicate distance and direction moved by the skin. Stipple indicates area of granulation tissue. Human skin contracts much less, leaving a greater relative area to be filled in by granulation tissue and scar.

FIGURE 2.5 Diagram illustrating contraction of the skin in rodent (A) vs human (B) circular excisional wounds. Outer circle = initial perimeter of the wound. Inner circle = position to which the skin is drawn by contraction. Arrows indicate distance and direction moved by the skin. Stipple indicates area of granulation tissue. Human skin contracts much less, leaving a greater relative area to be filled in by granulation tissue and scar.

to decrease the area that needs to be covered by epidermis and filled in by scar tissue. Contraction is characterized by the sliding and stretching of perilesional skin over the defect and should not be confused with contracture, which is the shortening of scar tissue, leading to deformity and loss of function. Dermal contraction accounts for a much greater percentage of wound closure in rodents than in pigs or humans (figure 2.5). In vivo, contraction accounts for up to ~90% of wound closure in mice (Yannas, 2001). In humans, less than 50% of excisional wound closure is due to contraction; the majority is due to scar tissue formation. In addition to dermis, contraction has been shown to help close wounds in peripheral nerve, ligaments, ureter, esophagus, and duodenum (Yannas, 2001).

The skin of developing frog tadpoles and fetal mammals regenerates in the absence of dermal contraction (see below), but as development proceeds, there is an increase in contraction accompanied by a decrease in the capacity for regeneration (Yannas, 1996, 2001). This implies an inverse relationship between the degree of contraction and the degree of regeneration. However, inhibiting wound contraction in mammals by pharmacological agents such as steroids does not lead to regeneration and the wound fills with granulation tissue (Yannas, 2001). Thus, although contraction reduces the area to be covered in adult wounds, it does not appear to be a causal factor in determining whether regeneration occurs.

Dermal contraction in mammals is initiated early in the phase of structural repair by fibroblasts that differentiate into myofibroblasts under the influence of TGF-p1 and ECM (Gabbiani, 1998; Lorena et al., 2002; Desmouliere et al., 2005). Myofibroblasts have characteristics of both fibroblasts and smooth muscle cells. Their contractile apparatus is like that of smooth muscle, consisting of large bundles of the a-smooth muscle form of actin microfilaments running along the inner surface of the plasma membrane (Rudolph et al., 1992; Clark, 1996). Myofibroblasts assemble Fn into fibrils at their surfaces and form fibronexi, transmembrane connections linking the actin microfilaments with the extracellular Fn fibrils (Newman and Tomasek, 1996; Tomasek et al., 1999). Treatment of fibroblasts in vitro with TGF-P1 increased the expression of av p1 integrins. Blocking the function of av and p1-contain-ing integrins with antibodies inhibited TGF-p1-induced smooth muscle actin expression and the ability of myofibroblasts to contract collagen gel, implicating the involvement of these integrins in the differentiation of myofibroblasts (Lygoe et al., 2004).

Interestingly, contraction takes place normally after excision of the central granulation tissue in back and flank skin wounds of guinea pigs (Gross, 1996). This suggests that the mechanism of contraction is one in which the coordinated action of myofibroblasts around the edge of the wound pulls the dermis inward.

Was this article helpful?

0 0
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.

Get My Free Ebook


Post a comment