Healing is the process whereby the cells in the body regenerate and repair to reduce the size of a damaged or necrotic area. Healing incorporates both the removal of necrotic tissue (demolition), and the replacement of this tissue.
The replacement can happen in two ways:
by regeneration: the necrotic cells are replaced by the same tissue as was originally there.
by repair: injured tissue is replaced with scar tissue.
Most organs will heal using a mixture of both mechanisms.
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In order for an injury to be healed by regeneration, the cell type that was destroyed must be able to replicate. Most cells have this ability, although it is believed that cardiac muscle cells and neurons are two important exceptions.
Cells also need a collagen framework along which to grow. Alongside most cells there is either a basement membrane or a collagenous network made by fibroblasts that will guide the cells' growth. Since ischaemia and most toxins do not destroy collagen, it will continue to exist even when the cells around it are dead.
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Healing must happen by repair in the case of injury to cells that are unable to regenerate (e.g. cardiac muscle or neurons). Also, damage to the collagen network (e.g. by enzymes or physical destruction), or its total collapse (as can happen in an infarct) cause healing to take place by repair.
Soon after injury, a wound healing cascade is unleashed. This cascade is usually said to take place in three phases: the inflam ...
