A tissue's ability to repair injury depends partly on the proliferative capacity of its cells and the preservation of its supporting framework.
Continuously renewing tissues
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Hematopoietic cells in bone marrow and many surface epithelia continually replace lost cells using tissue stem cells and remaining mature cells.
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Examples include the basal layers of the skin's squamous epithelium and the columnar epithelium of the gastrointestinal tract.
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These tissues readily regenerate after injury if their stem cell pool is preserved.
Normally quiescent cells
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Cells in the parenchyma of organs such as the liver, kidney, and pancreas normally remain in the G0 stage of the cell cycle but can divide after injury or loss of tissue mass.
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Endothelial cells, fibroblasts, and smooth muscle cells are normally quiescent but can proliferate in response to growth factors, an important reaction in wound healing.
Nonproliferative cells and structural damage
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Most neurons and cardiac muscle cells are terminally differentiated and nonproliferative. Injury is irreversible and usually results in scarring because these cells cannot regenerate.
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Mild injury confined to the epithelium can resolve by regeneration when the underlying tissue remains intact.
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More severe injury that damages the connective tissue framework heals by scar formation.