Response of the Integument to Injuries and Wounds

Response of the Integument to Injuries and Wounds

The integument responds to injuries and wounds with inflammation, which causes redness, increased warmth, and painful swelling. The blood vessels of the wounded area dilate and allow fluids to leak into the damaged tissues. This provides more nutrients and oxygen to the tissues, aiding in healing. Shallow breaks in the skin cause epithelial cells to divide more rapidly, with the new cells filling the break.

A cut that extends into the dermis or subcutane-ous layers breaks blood vessels. The escaping blood then forms a clot in the wound, eventually forming a scab as it dries. The scab protects the underlying tissues. Cells called fibroblasts move to the injury to form new collagenous fibers that bind the edges of the wound together. Large skin breaks may require suturing or other methods of closing them more com-pletely, which actually helps to speed up the action of the fibroblasts in healing.

Wound healing proceeds as blood vessels extend into the area below the scab, with phagocytic cells removing dead cells and debris. As tissue is replaced, the scab eventually falls off. Extensive wounds may cause the newly formed tissue to appear on the skin surface as a scar. Large open wounds may develop small round masses called granulations, which consist of new blood vessel branches and clusters of fibroblasts. Once the fibroblasts eventually move away, the resultant scar is mostly composed of collagenous fibers.

If a wound is large or occurs in an area where the skin is thin, epithelial cells cannot cover the surface until dermal repairs are already under way. Circulation to the area is enhanced so that blood clotting, fibroblasts, and an extensive capillary network can combine to combat the injury. (Together, these components are known as granulation tissue.) Repairs do not restore the dermis to its original condition, and collagen fibers dominate with relatively few new blood vessels. Scar tissue is relatively inflexible and noncellular. Thickened, raised scar tissue is referred to as a keloid, featuring a shiny and smooth surface. Keloids are harmless but unsightly.