The Irreversibility of Organ Injury - Tissue and Organ Regeneration in Adults - page 1

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The Irreversibility of Organ Injury

1.1 Repair vs. Regeneration

Organ regeneration is distinct from organ repair as an endpoint of a healing process
following injury. Repair heals the interrupted continuity of tissues by contraction
of wound edges and synthesis of scar tissue without restoration of the normal tis-
sues. In contrast, regeneration heals by synthesis of the missing organ mass at the
original anatomical site, yielding a regenerate, not scar. Regeneration restores the
normal structure and function of the organ; repair does not. An identical distinction
between repair and regeneration has been also made by Goss (1992a). Alternative
uses of these terms appear sometimes in the literature of wound healing. Through-
out this volume we will use the above definitions.
An adult typically responds to chronic and acute injury (trauma) by repairing the
injured anatomical site. Trauma is acute injury caused by an external energy source,
usually acting destructively for seconds or minutes. Chronic injury is the end result
of a prolonged sequence of biochemical insults, typically extending over years,
such as those leading to liver cirrhosis. Acute and chronic injury often have a com-
mon outcome—loss of organ function. Response to chronic injury, caused by viral
or toxic agents, is much harder to study experimentally than the response to acute
injury; for this reason, the emphasis in this volume will be on response to trauma.
Regeneration may be spontaneous , taking place entirely by itself, unaided by
the experimenter or it may be induced , i.e., deliberately provoked using exogenous
agents. Although spontaneous regeneration is a basic topic that is treated in this vol-
ume, a major focus is the phenomenon of induced regeneration following acute injury.

1.2 Tissues and Organs

The anatomical terms used in this volume usually follow the nomenclature used
either in Wheater's Functional Histology (Young et al. 2006) or in Histology and
Cell Biology (Kierszenbaum and Tres 2012).