Morphology of healing tissue and factors delaying wound repair
THE CONTEXT
Granulation tissue develops at an injury site and progresses toward a collagen-rich scar. Infection, metabolic disease, nutritional deficiency, and glucocorticoids can interfere with repair.
Granulation tissue and mature scar
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Granulation tissue contains proliferating fibroblasts, thin-walled delicate capillaries, and loose extracellular matrix (ECM), often with inflammatory cells, mainly macrophages.
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The amount of granulation tissue depends on the size of the tissue deficit and the intensity of inflammation.
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A healing wound shows numerous blood vessels, edema, loose ECM, occasional inflammatory cells, and minimal mature collagen.
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A scar or fibrotic tissue contains inactive spindle-shaped fibroblasts, dense collagen bundles, and other ECM components. Mature scars may contain scattered vascular channels.
Stains and matrix constituents
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Trichrome stain detects collagen fibers and colors collagen blue, muscle red, and red blood cells orange.
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Elastin stain identifies delicate elastin fibers, which form the major component of pliable elastic tissue.
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Reticulin is composed of type III collagen, contributes to the connective tissue stroma of normal organs, and is present in early scars. It can be identified with a special stain.
Factors that impair repair
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Factors preventing healing may be extrinsic or intrinsic to the injured tissue and may act systemically or locally.
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Infection is a clinically important cause of delayed healing because it prolongs inflammation and may increase local tissue injury.
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Diabetes is an important systemic cause of delayed wound healing and compromises tissue repair.
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Protein and vitamin C deficiencies inhibit collagen synthesis and retard healing.
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Glucocorticoids inhibit production of transforming growth factor-b (TGF-b), which promotes collagen deposition. Their administration after surgery may therefore prevent adequate wound healing.