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
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
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
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...
, 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
Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...
, healing is the process by which
neuroses
Neurosis is a class of functional mental disorders involving chronic distress, but neither delusions nor hallucinations. The term is no longer used by the professional psychiatric community in the United States, having been eliminated from t ...
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
A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
treatment or
alternative
Alternative or alternate may refer to:
Arts, entertainment and media
* Alternative (''Kamen Rider''), a character in the Japanese TV series ''Kamen Rider Ryuki''
* ''The Alternative'' (film), a 1978 Australian television film
* ''The 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
Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
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
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
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
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
(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
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s 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
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,
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsk ...
es and
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
. Clotting is followed by
neutrophil
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...
invasion three to 24 hours after the wound has been incurred, with
mitoses beginning in
epithelial
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...
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 hormone
Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...
s 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
Granulation tissue is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any siz ...
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
eicosanoids 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
adrenal gland
The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex ...
s increase production of
cortisol which shuts down eicosanoid production and inflammation.
Resolution phase
In the Resolution phase, pathogens and damaged tissue are removed by
macrophages (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
lipoxins,
epi-lipoxins, and
resolvins, which cause release of growth hormones.
See also
*
Scar free healing
*
Health
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organ ...
References
External links
How wounds heal and tumors formWith this simple Flash demonstration, Harvard professor Donald Ingber explains how wounds heal, why scars form, and how tumors develop. Presented by Children's Hospital Boston.
* Lorenz H.P. and Longaker M.T.
Wounds: Biology, Pathology, and Management Stanford University Medical Center.
* Romo T. and McLaughlin L.A. 2003
Emedicine.com.
* Rosenberg L. and de la Torre J. 2003
Emedicine.com.
After the Injury- Children's Hospital Of Philadelphia
{{Authority control
Injuries
Medical phenomena
Physiology
Therapy