The process by which the body repairs bone, tissue, or organ damage caused by injury, infection, or disease. The initial stages of healing are the same in all parts of the body. After injury, blood clots form in damaged tissues. White blood cells, enzymes, histamine, other chemicals, and proteins from which new cells can be made accumulate at the site of damage. Fibrous tissue is laid down within the blood clot to form a supportive structure, and any dead cells are broken down and absorbed by the white blood cells. Some tissues, such as bone and skin, are then able to regenerate by the proliferation of new cells around the damaged area. In skin injuries, the fibrous tissue shrinks as new skin forms underneath. The tissue hardens to form a scab, which falls off when new skin growth is complete. A scar may remain. An inadequate blood supply or persistent infection prevents regeneration, and some tissues, such as nerve tissue, may be unable to regenerate. In these cases, the fibrous tissue may develop into tough scar tissue, which keeps the tissue structure intact but may impair its function.


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