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 Human body regenerate and repair to reduce the size of a damaged or necrosis 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. 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 Psychopathology phenomena. This process may involve psychotherapy, pharmaceutical treatment or alternative approaches such as Holistic health.
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
that will guide the cells' growth. Since
ischaemia and most
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
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
,
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 Microscope.
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 or physical destruction), or its total collapse (as can happen in an infarct) cause healing to take place by repair Somatic psychology
.
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
In response to an incision or wound, a
Wound healing 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,
and
fungi. Clotting is followed by
neutrophil invasion three to 24 hours after the wound has been incurred, with
mitosis beginning in
epithelium cells after 24 to 48 hours.
Inflammation phase
In the inflammatory phase,
and other
phagocytosis cells kill bacteria, debride damaged tissue and release chemical factors such as
that encourage fibroblasts,
and endothelial cells which make new
capillary 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.
Maturation phase
During the maturation phase of wound healing, unnecessary vessels formed in granulation tissue are removed by
apoptosis, and type III collagen is largely replaced by type I. Collagen which was originally disorganized is cross-linked and aligned along tension lines. This phase can last a year or longer. Ultimately a scar made of collagen, containing a small number of fibroblasts is left.
Tissue damaged by inflammation
After inflammation has damaged tissue (when combatting bacterial infection for example) and pro-inflammatory
have completed their function, healing proceeds in 4 phases.
[ The Anti-Inflammation Zone, Barry Sears, pages 230–233, 2005.]
Recall phase
In the recall phase the
increase production of
cortisol which shuts down eicosanoid production and inflammation.
Resolution phase
In the Resolution phase, pathogens and damaged tissue are removed by
(white blood cells). Red blood cells are also removed from the damaged tissue by macrophages. Failure to remove all of the damaged cells and pathogens may retrigger inflammation. The two subsets of macrophage M1 & M2 plays a crucial role in this phase, M1 macrophage being a pro inflammatory while as M2 is a regenerative and the plasticity between the two subsets determine the tissue inflammation or repair.
Regeneration phase
In the Regeneration phase, blood vessels are repaired and new cells form in the damaged site similar to the cells that were damaged and removed. Some cells such as neurons and muscle cells (especially in the heart) are slow to recover.
Repair phase
In the Repair phase, new tissue is generated which requires a balance of anti-inflammatory and pro-inflammatory eicosanoids. Anti-inflammatory eicosanoids include
,
, and
, which cause release of growth hormones.
See also
External links
