4
Chapter 4
Tissue: The Living Fabric
143
Te repair process that we have just described follows heal-
ing of a wound (cut, scrape, puncture) that breaches an epithe-
lial barrier. In simple
infections
(a pimple or sore throat), healing
is solely by regeneration. Only severe (destructive) infections
lead to clot formation or scarring.
epithelium thickens until it finally resembles the adjacent
skin. Te end result is a fully regenerated epithelium, and an
underlying area of scar tissue. Te scar may be invisible, or
visible as a thin white line, depending on the severity of the
wound.
Regeneration and fibrosis effect
permanent repair:
• The fbrosed area matures and
contracts; the epithelium thickens.
• A Fully regenerated epithelium with
an underlying area oF scar tissue results.
Regenerated epithelium
Fibrosed area
Inflammation sets the stage:
• Severed blood vessels bleed.
• In±ammatory chemicals are released.
• Local blood vessels become more permeable,
allowing white blood cells, ±uid, clotting
proteins, and other plasma proteins to seep
into the injured area.
• Clotting occurs; surFace dries and Forms a scab.
Scab
Blood clot in
incised wound
Epidermis
Vein
Inflammatory
chemicals
Migrating
white
blood cell
Artery
Organization restores the blood supply:
• The clot is replaced by granulation
tissue, which restores the vascular
supply.
• ²ibroblasts produce collagen fbers that
bridge the gap.
• Macrophages phagocytize dead and
dying cells and other debris.
• SurFace epithelial cells multiply and
migrate over the granulation tissue.
Regenerating
epithelium
Area of
granulation
tissue
ingrowth
Fibroblast
Macrophage
Budding
capillary
3
2
1
Figure 4.12
Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
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