ResidentNet/Basic Science/New Tissue

WOUND HEALING: NEW TISSUE FORMATION
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Collagen, however, cannot be synthesized in the absence of adequate oxygen supply. But the wound has derailed blood flow. Angiogenesis is required. Through their enzymatic actions, growth factors break down the vascular membrane of the venules. Endothelial cells that migrate through the defect aggregate to form vascular buds (click on image to download a 98K Quicktime movie).

Buds connect with contiguous buds to form loops. Loops develop a basal membrane from extracellular matrix components and then develop their own vascular buds. This process continues until -- Voila! Contact is made with an intact blood vessel and a capillary loop forms with directed blood flow (image expandable to 58K GIF).

New highly vascularized tissue has a granular appearance (which may be why it's called granulated tissue), and is recognizable by its visible pinhead-size rounded nodules. Nodules that are dark red in color and appear moist and shiny indicate good healing. Poor healing is indicated by a bluish color and a smeary fibrin appearance (image expandable to 36K JPEG).

Collagenase, synthesized by fibroblasts, keeps collagen production in check, and has a critical function in the process of collagen maturation. Part of the process of collagen maturation includes developing cross-links, which give collagen and the scar strength and to reorganize collagen in a less chaotic way and more along the lines of contour stress. (Image expandable to 54K JPEG).

Having formed abundant collagen fibers, the fibroblasts transform either into fibrocytes or myofibroblasts, the latter has contractile properties. Consequently the collagen fibers tighten. The end result of the process? Shrinking scar tissue! (Image expandable to 36K JPEG).

Ah . . .but the wound surface, you wonder. Repair of the epithelium is needed to keep the undesirables out and the vital essentials -- body fluids and electrolytes, for example -- from escaping. (Image expandable to 46K JPEG)

Within 24 hours of wounding, the basal cell layer of the epidermis adjacent to the wound thickens and marginal cells elongate and migrate over the wound. The cells at the advancing epithelial edge are followed by a monolayer of new epithelial cells that advance across the wound until they eventually meet epithelial cells moving in from the opposite direction. (Sort of like the meeting of the transcontinental railroad.) (Click on image to download Quicktime movie)

The price of wound repair is a scar, which appears reddish at first but as the connective tissue grows tauter and vascularization slows, it gradually looses color. Hair, sebaceous and sweat glands are also absent, as is the ridged pattern of the epidermis. Thus the new skin's appearance is unusually smooth. (Image expandable to 36K JPEG)

Go back to the first page of New Tissue Formation

Please see Wound Healing in Specific Tissues