Healing
Regarding physical trauma or disease suffered by an organism, healing involves the repairing of damaged tissue, organs and the biological system as a whole and resumption of 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.
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
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, or by toxins.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. Also, damage to the collagen network, or its total collapse 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 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
In response to an incision or wound, a wound healing cascade is unleashed. This cascade takes place in four phases: clot formation, inflammation, proliferation, and maturation.Clotting phase
Healing of a wound begins with clot formation to stop bleeding and to reduce infection by bacteria, viruses and fungi. Clotting is followed by neutrophil invasion three to 24 hours after the wound has been incurred, with mitoses beginning in epithelial cells after 24 to 48 hours.Inflammation phase
In the inflammatory phase, macrophages and other phagocytic cells kill bacteria, debride damaged tissue and release chemical factors such as growth hormones that encourage fibroblasts, epithelial cells and endothelial cells which make new capillaries to migrate to the area and divide.Proliferative phase
In the proliferative phase, immature granulation tissue containing plump, active fibroblasts forms. Fibroblasts quickly produce abundant type III collagen, which fills the defect left by an open wound. Granulation tissue moves, as a wave, from the border of the injury towards the center.As granulation tissue matures, the fibroblasts produce less collagen and become more spindly in appearance. They begin to produce the much stronger type I collagen. Some of the fibroblasts mature into myofibroblasts which contain the same type of actin found in smooth muscle, which enables them to contract and reduce the size of the wound.