healing healing with physical trauma or disease suffered by an organism, healing involves the repairing of damaged tissue(s), organs and the biological system as a whole and resumption of (normal) functioning. medicine includes the process by which the cells in the body regenerate and repair to reduce the size of a damaged or necrotic area and replace it with new living tissue. the replacement can happen in two ways: by regeneration in which the necrotic cells are replaced by new cells that form "like" tissue as was originally there; or by repair in which injured tissue is replaced with scar tissue. most organs will heal using a mixture of both mechanisms. diagram featuring stages of tissue healing within surgery, healing is more often referred to as recovery, and postoperative recovery has historically been viewed simply as restitution of function and readiness for discharge. more recently, it has been described as an energy‐requiring process to decrease physical symptoms, reach a level of emotional well‐being, regain functions, and re‐establish activities healing is also referred to in the context of the grieving process. in psychiatry and psychology, healing is the process by which neuroses and psychoses are resolved to the degree that the client is able to lead a normal or fulfilling existence without being overwhelmed by psychopathological phenomena. this process may involve psychotherapy, pharmaceutical treatment or alternative approaches such as traditional spiritual healing. regeneration in order for an injury to be healed by regeneration, the cell type that was destroyed must be able to replicate. 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. example acute tubular necrosis (atn) in the kidney is a case in which cells heal completely by regeneration. atn occurs when the epithelial cells 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 antibiotics, heavy metals or carbon tetrachloride). 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. 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 microscopically. 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 enzymes or physical destruction), or its total collapse (as can happen in an infarct) cause healing to take place by repair. genetics many genes play a role in healing. for instance, in wound healing, p21 has been found to allow mammals to heal spontaneously. it even allows some mammals (like mice) to heal wounds without scars. the lin28 gene also plays a role in wound healing. it is dormant in most mammals. also, the proteins mg53 and tgf beta 1 play important roles in wound healing. wound healing main article: wound healing