Healing

===Example===
[[Acute tubular necrosis]] (ATN) in the [[kidney]] is a case in which cells heal completely by regeneration. ATN occurs when the [[epithelial cell]]s that line the kidney are destroyed by either a lack of [[oxygen]] (such as in [[hypovolemic shock]], when blood supply to the kidneys is dramatically reduced), or by toxins (such as some [[antibiotic]]s, [[heavy metals]] or [[carbon tetrachloride]]).{{Citation needed|date=May 2022}}

Although many of these epithelial cells are dead, there is typically patchy necrosis, meaning that there are patches of epithelial cells still alive. In addition, the collagen framework of the tubules remains completely intact.{{Citation needed|date=May 2022}}

The existing epithelial cells can replicate, and, using the basement membrane as a guide, eventually bring the kidney back to normal. After regeneration is complete, the damage is undetectable, even [[Microscope|microscopically]].{{Citation needed|date=May 2022}}

Healing must happen by repair in the case of injury to cells that are unable to regenerate (e.g. neurons). Also, damage to the collagen network (e.g. by [[enzyme]]s or physical destruction), or its total collapse (as can happen in an [[infarct]]) cause healing to take place by repair.{{Citation needed|date=May 2022}}