Regeneration as a property of living things: the ability for self-renewal and restoration. Types of regeneration
Regeneration (in pathology) is the restoration of the integrity of tissues damaged by any disease process or external traumatic influence. Recovery occurs due to neighboring cells, filling the defect with young cells and their subsequent transformation into mature tissue. This form is called reparative (compensatory) regeneration. In this case, two options for regeneration are possible: 1) the loss is compensated by tissue of the same type as the one that died (complete regeneration); 2) the loss is replaced by young connective (granulation) tissue, which turns into scar tissue (incomplete regeneration), which is not regeneration in the proper sense, but the healing of a tissue defect.
Regeneration is preceded by the release of a given area from dead cells by enzymatic melting and absorption into the lymph or blood or by (see). Melting products are one of the stimulators of the proliferation of neighboring cells. In many organs and systems there are areas whose cells are a source of cell proliferation during regeneration. For example, in the skeletal system such a source is the periosteum, the cells of which, when multiplying, first form osteoid tissue, which later turns into bone; in the mucous membranes - cells of deep-lying glands (crypts). Regeneration of blood cells occurs in the bone marrow and outside it in the system and its derivatives (lymph nodes, spleen).
Not all tissues have the ability to regenerate, and not to the same extent. Thus, the muscle cells of the heart are not capable of reproduction, resulting in the formation of mature muscle fibers, therefore any defect in the myocardial muscles is replaced by a scar (in particular, after a heart attack). When brain tissue dies (after hemorrhage, arteriosclerotic softening), the defect is not replaced by nervous tissue, but a tissue is formed.
Sometimes the tissue that appears during regeneration differs in structure from the original (atypical regeneration) or its volume exceeds the volume of dead tissue (hyperregeneration). This course of the regeneration process can lead to tumor growth.
Regeneration (Latin regenerate - revival, restoration) - restoration of the anatomical integrity of an organ or tissue after the death of structural elements.
Under physiological conditions, regeneration processes occur continuously with varying intensity in different organs and tissues, according to the intensity of the aging of the cellular elements of a given organ or tissue and their replacement with newly formed ones. Formed elements of the blood, cells of the integumentary epithelium of the skin, mucous membranes of the gastrointestinal tract, and respiratory tract are continuously replaced. Cyclic processes in the female reproductive system lead to rhythmic rejection and renewal of the endometrium through its regeneration.
All these processes are the physiological prototype of pathological regeneration (it is also called reparative). Features of the development, course and outcome of reparative regeneration are determined by the extent of tissue death and the nature of pathogenic influences. The last circumstance must be especially borne in mind, since the conditions and causes of tissue death are essential for the regeneration process and its outcomes. For example, scars after skin burns have a special character, different from scars of other origins; syphilitic scars are rough, lead to deep retractions and disfigurement of the organ, etc. Unlike physiological regeneration, reparative regeneration covers a wide range of processes leading to compensation of the defect caused by the loss of tissue due to its damage. A distinction is made between complete reparative regeneration - restitution (replacement of the defect with tissue of the same type and the same structure as the dead one) and incomplete reparative regeneration (filling the defect with tissue that has greater plastic properties than the dead one, i.e. ordinary granulation tissue and connective tissue with further turning it into scar tissue). Thus, in pathology, regeneration often means healing.
The concept of regeneration is also associated with the concept of organization, since both processes are based on the general laws of new tissue formation and the concept of substitution, i.e. displacement and replacement of pre-existing tissue by newly formed tissue (for example, substitution of a blood clot with fibrous tissue).
The degree of completeness of regeneration is determined by two main factors: 1) the regenerative potential of a given tissue; 2) the volume of the defect and the same or heterogeneous species of dead tissue.
The first factor is often associated with the degree of differentiation of a given tissue. However, the very concept of differentiation and the content of this concept are very relative, and comparison of tissues on this basis with the establishment of a quantitative gradation of differentiation in functional and morphological terms is impossible. Along with tissues that have a high regenerative potential (for example, liver tissue, mucous membranes of the gastrointestinal tract, hematopoietic organs, etc.), there are organs with an insignificant potential for regeneration, in which regeneration never ends with complete restoration of lost tissue (for example, myocardium , CNS). Connective tissue, wall elements of the smallest blood and lymphatic vessels, peripheral nerves, reticular tissue and its derivatives have extremely high plasticity. Therefore, plastic irritation, which is trauma in the broad sense of the word (that is, all its forms), first and foremost stimulates the growth of these tissues.
The volume of dead tissue is essential for the completeness of regeneration, and the quantitative limits of tissue loss for each organ, which determine the degree of restoration, are more or less known empirically. It is believed that for the completeness of regeneration, not only volume as a purely quantitative category is important, but also the complex diversity of dead tissues (this especially applies to tissue death caused by toxic-infectious influences). To explain this fact, one should, apparently, turn to the general patterns of stimulation of plastic processes under pathological conditions: the stimulators are the products of tissue death themselves (hypothetical “necrohormones”, “mitogenetic rays”, “trephons”, etc.). Some of them are specific stimulators for cells of a certain type, others are nonspecific, stimulating the most plastic tissues. Nonspecific stimulants include products of the breakdown and vital activity of leukocytes. Their presence during reactive inflammation, which always develops with the death of not only parenchymal elements, but also the vascular stroma, promotes the proliferation of the most plastic elements - connective tissue, i.e., the eventual development of a scar.
There is a general scheme for the sequence of regeneration processes, regardless of the area where it occurs. Under pathological conditions, regeneration processes in the narrow sense of the word and healing processes are of a different nature. This difference is determined by the nature of tissue death and the selective direction of action of the pathogenic factor. Pure forms of regeneration, i.e. restoration of tissue identical to the lost one, are observed in cases where, under the influence of pathogenic influence, only specific parenchymal elements of an organ die, provided they have a high regenerative potency. An example of this is the regeneration of renal tubular epithelium selectively damaged by toxic exposure; regeneration of the epithelium of the mucous membranes during desquamation; regeneration of lung alveolocytes in desquamative catarrh; regeneration of skin epithelium; regeneration of the endothelium of blood vessels and endocardium, etc. In these cases, the source of regeneration is the remaining cellular elements, the reproduction, maturation and differentiation of which leads to complete replacement of the lost parenchymal elements. When complex structural complexes die, restoration of lost tissue occurs from special areas of the organ, which are unique regeneration centers. In the intestinal mucosa, in the endometrium, such centers are glandular crypts. Their multiplying cells cover the defect first with one layer of undifferentiated cells, from which glands then differentiate and the structure of the mucosa is restored. In the skeletal system, such a regeneration center is the periosteum, in the integumentary squamous epithelium - the Malpighian layer, in the blood system - bone marrow and extramedullary derivatives of reticular tissue.
The general law of regeneration is the law of development, according to which, in the process of neoplasm, young undifferentiated cellular derivatives arise, which subsequently undergo stages of morphological and functional differentiation up to the formation of mature tissue.
The death of areas of an organ consisting of a complex of various tissues causes reactive inflammation (see) along the periphery. This is an adaptive act, since the inflammatory reaction is accompanied by hyperemia and increased tissue metabolism, which promotes the growth of newly formed cells. In addition, inflammatory cellular elements from the group of histophagocytes are plastic material for the formation of connective tissue.
In pathology, anatomical healing is often achieved with the help of granulation tissue (see) - the stage of new formation of a fibrous scar. Granulation tissue develops during almost any reparative regeneration, but the degree of its development and final outcomes vary within very wide limits. Sometimes these are tender areas of fibrous tissue that are difficult to distinguish during microscopic examination, sometimes they are coarse dense strands of hyalinized bradytrophic scar tissue, often subject to calcification (see) and ossification.
In addition to the regenerative potential of a given tissue, the nature of its damage, its volume, general factors are important in the regeneration process. These include the age of the subject, the nature and characteristics of nutrition, and the general reactivity of the body. In case of innervation disorders or vitamin deficiencies, the usual course of reparative regeneration is distorted, which is most often expressed in a slowdown in the regeneration process and sluggishness of cellular reactions. There is also the concept of fibroplastic diathesis as a constitutional feature of the body to respond to various pathogenic irritations with increased formation of fibrous tissue, which is manifested by the formation of keloid (see), adhesive disease. In clinical practice, it is important to take into account general factors to create optimal conditions for the completeness of the regeneration process and healing.
Regeneration is one of the most important adaptive processes that ensure the restoration of health and continuation of life under emergency circumstances created by the disease. However, like any adaptive process, regeneration at a certain stage and along certain paths of development can lose its adaptive significance and itself create new forms of pathology. Disfiguring scars that deform an organ and sharply impair its function (for example, cicatricial transformation of heart valves as a result of endocarditis) often create severe chronic pathology that requires special therapeutic measures. Sometimes the newly formed tissue quantitatively exceeds the volume of the dead tissue (super-regeneration). In addition, in every regenerate there are elements of atypia, the sharp severity of which is a stage of tumor development (see). Regeneration of individual organs and tissues - see the relevant articles on organs and tissues.
There are two types of regeneration - physiological and reparative.
Physiological regeneration- continuous updating of structures on
cellular (replacement of blood cells, epidermis, etc.) and intracellular (renewal
cellular organelles) levels that ensure the functioning of organs and
Reparative regeneration- process of eliminating structural damage
after the action of pathogenic factors.
Both types of regeneration are not separate, independent of each other.
Regeneration value for the organism is determined by the fact that, on the basis of cellular
and intracellular renewal of organs provides a wide range
adaptive fluctuations in their functional activity in changing
environmental conditions, as well as restoration and compensation of damaged
under the influence of various pathogenic factors of functions.
Regeneration process deployed at different levels of the organization -
systemic, organ, tissue, cellular, intracellular. Implemented
through direct and indirect cell division, renewal of intracellular
organelles and their reproduction. Update intracellular structures and their
hyperplasia are a universal form of regeneration, inherent in all without
exceptions to mammalian and human organs. It is expressed either in the form
intracellular regeneration itself, when after the death of part of the cell its
the structure is restored due to the proliferation of surviving organelles, or
in the form of an increase in the number of organelles (compensatory hyperplasia of organelles) in
one cell upon the death of another.
Restoration of the original mass of the organ after its damage is carried out
in various ways. In some cases, the remaining part of the organ remains
unchanged or little changed, and the missing part grows back from the wound
surface in the form of a clearly demarcated regenerate. This way
restoration of the lost part of an organ is called e pymorphosis. In others
In cases, a restructuring of the remaining part of the organ occurs, during which
it gradually acquires its original shape and size. This process option
regeneration is called morphallaxis. More often epimorphosis and morphallaxis
found in various combinations. Observing an increase in organ size
after its damage, previously they talked about its compensatory hypertrophy.
Cytological analysis of this process showed that it is based on
cell reproduction, i.e. regenerative reaction. In this regard, the process
called “regenerative hypertrophy”.
The effectiveness of the regeneration process is largely determined by the conditions in which
which it flows. The general condition is important in this regard.
body. Depletion, hypovitaminosis, innervation disorders, etc. have
significant influence on the course of reparative regeneration, inhibiting it and
contributing to the transition to pathological. Significant impact on intensity
reparative regeneration is influenced by the degree of functional load,
correct dosage which favors this process. Speed
reparative regeneration is to a certain extent determined by age, which
is of particular importance due to increasing life expectancy and
accordingly, the number of surgical interventions in people of older age groups.
Usually, no significant deviations in the regeneration process are noted and
The severity of the disease and its complications seem to be more important than
age-related weakening of regenerative ability
Changing the general and local conditions in which the regeneration process takes place,
can lead to both quantitative and qualitative changes.
Numerous endo- and
exogenous nature. Antagonistic influences of various factors have been established
on the course of intracellular regenerative and hyperplastic processes.
The influence of various hormones on regeneration has been most studied. Regulation
mitotic activity of cells of various organs is carried out by hormones
adrenal cortex, thyroid gland, gonads, etc. An important role in
in this regard they play the so-called. gastrointestinal hormones. Known powerful
endogenous regulators of mitotic activity - keylons, proslandins, their
antagonists and other biologically active substances.
Conclusion
An important place in research into the mechanisms of regulation of regeneration processes
occupies the study of the role of various parts of the nervous system in their course and
outcomes. A new direction in the development of this problem is the study
immunological regulation of regeneration processes, and in particular the establishment
the fact of the transfer of “regenerative information” by lymphocytes, stimulating
proliferative activity of cells of various internal organs.
The regulatory influence on the course of the regeneration process is also exerted by
The main problem is that tissue regeneration in humans occurs
So slow. Too slow for recovery to occur
really significant damage. If this process had succeeded at least
speed it up a little, the result would be much more significant.
Knowledge of the mechanisms regulating the regenerative capacity of organs and tissues
opens up prospects for developing the scientific basis for stimulating reparative
regeneration and management of healing processes.
Types of regeneration: physiological, reparative and pathological.
Physiological regeneration is not associated with the action of any damaging factor and is carried out using apoptosis. Apoptosis is the genetically programmed death of a cell in a living organism. No inflammatory reaction occurs.
Reparative regeneration occurs when various damaging factors (trauma, inflammation) occur. Complete regeneration, or restitution, is complete structural and functional restoration; incomplete regeneration, or substitution, occurs in organs with an intracellular form of regeneration and in organs with a mixed form of regeneration, but with extensive damage.
Pathological regeneration can be excessive (hyperregeneration), slow (hyporegeneration), metaplasia and dysplasia. Excessive regeneration occurs with pronounced activation of the first phase of regeneration. Hyporegeneration occurs when the proliferation phase is sluggish. This occurs in organs and tissues where there is chronic inflammation and where the processes of vascular and nervous trophism are often disrupted. Metaplasia occurs in organs and tissues with a cellular form of regeneration, and is often preceded by chronic inflammation. With anemia and blood diseases, metaplasia of yellow bone marrow into red occurs. This is a compensatory mechanism. Dysplasia occurs when proliferation and differentiation of cells are impaired, so atypical cells appear, i.e., having different shapes and sizes, having large hyperchromic nuclei. Such cells appear among ordinary epithelial cells.
There are three degrees of dysplasia: mild, moderate, severe (when almost all cells of the epithelial layer become atypical and are diagnosed as cancer in situ).
During the regeneration of connective tissue, there are 3 stages.
1. Formation of young, immature connective – granulation – tissue.
2. Formation of fibrous connective tissue.
3. Formation of scar connective tissue, which contains thick, coarse collagen fibers.
Wound healing refers to reparative regeneration. There are four types: direct closure of the defect by creeping epithelium, healing under the scab, healing by primary and secondary intention. Direct closure of a defect in the epithelial cover is the simplest healing, which consists of creeping the epithelium onto the surface defect and covering it with an epithelial layer. Healing under a scab concerns small defects, on the surface of which a drying crust (scab) of coagulated blood and lymph appears.
Primary intention is the healing of deep wounds with damage not only to the skin, but also to deep-lying tissues; scar on the 10-15th day. Wounds that are infected, crushed, contaminated and with uneven edges heal by secondary intention; heal through cleansing by leukocytes and macrophages on the 5-6th day.
Regeneration(from Latin regeneratio - rebirth) - the process of restoration by the body of lost or damaged structures. Regeneration maintains the structure and functions of the body, its integrity. There are two types of regeneration: physiological and reparative. The restoration of organs, tissues, cells or intracellular structures after their destruction during the life of the body is called physiological regeneration. Restoration of structures after injury or other damaging factors is called reparative regeneration. During regeneration, processes such as determination, differentiation, growth, integration, etc. occur, similar to the processes that take place in embryonic development. However, during regeneration, they all come secondarily, i.e. in a formed organism.
Physiological regeneration is the process of updating the functioning structures of the body. Thanks to physiological regeneration, structural homeostasis is maintained and the organs can constantly perform their functions. From a general biological point of view, physiological regeneration, like metabolism, is a manifestation of such an important property of life as self-renewal.
An example of physiological regeneration at the intracellular level is the processes of restoration of subcellular structures in the cells of all tissues and organs. Its significance is especially great for the so-called “eternal” tissues that have lost the ability to regenerate through cell division. This primarily applies to nervous tissue.
Examples of physiological regeneration at the cellular and tissue levels are the renewal of the epidermis of the skin, the cornea of the eye, the epithelium of the intestinal mucosa, peripheral blood cells, etc. The derivatives of the epidermis are renewed - hair and nails. This is the so-called proliferative regeneration, i.e. replenishment of the number of cells due to their division. In many tissues there are special cambial cells and foci of their proliferation. These are crypts in the epithelium of the small intestine, bone marrow, proliferative zones in the epithelium of the skin. The intensity of cellular renewal in these tissues is very high. These are the so-called “labile” tissues. All red blood cells of warm-blooded animals, for example, are replaced in 2-4 months, and the epithelium of the small intestine is completely replaced in 2 days. This time is required for the cell to move from the crypt to the villus, perform its function and die. Cells of organs such as the liver, kidney, adrenal gland, etc., renew themselves much more slowly. These are the so-called “stable” fabrics.
The intensity of proliferation is judged by the number of mitoses per 1000 counted cells. If we consider that mitosis itself lasts on average about 1 hour, and the entire mitotic cycle in somatic cells lasts on average 22-24 hours, then it becomes clear that in order to determine the intensity of renewal of the cellular composition of tissues it is necessary to count the number of mitoses over one or several days . It turned out that the number of dividing cells is not the same at different times of the day. So it was opened daily rhythm of cell divisions, an example of which is shown in Fig. 8.23.
Rice. 8.23. Daily changes in the mitotic index (MI)
in the epithelium of the esophagus ( I) and cornea ( 2 ) mice.
The mitotic index is expressed in ppm (0 / 00), reflecting the number of mitoses
per thousand cells counted
A daily rhythm in the number of mitoses was found not only in normal but also in tumor tissues. It is a reflection of a more general pattern, namely the rhythm of all body functions. One of the modern areas of biology is chronobiology - studies, in particular, the mechanisms of regulation of daily rhythms of mitotic activity, which is very important for medicine. The existence of a daily periodicity in the number of mitoses indicates the adjustability of physiological regeneration by the body. In addition to daily allowances, there are lunar and annual cycles of tissue and organ renewal.
There are two phases in physiological regeneration: destructive and restorative. It is believed that the breakdown products of some cells stimulate the proliferation of others. Hormones play a major role in regulating cellular renewal.
Physiological regeneration is inherent in organisms of all species, but it occurs especially intensively in warm-blooded vertebrates, since they generally have a very high intensity of functioning of all organs compared to other animals.
Reparative(from Latin reparatio - restoration) regeneration occurs after damage to a tissue or organ. It is very diverse in terms of the factors causing damage, the amount of damage, and the methods of recovery. Mechanical trauma, such as surgery, exposure to toxic substances, burns, frostbite, radiation exposure, fasting, and other pathogenic agents, are all damaging factors. Regeneration after mechanical trauma has been most widely studied. The ability of some animals, such as hydra, planaria, some annelids, starfish, sea squirts, etc., to restore lost organs and parts of the body has long amazed scientists. Charles Darwin, for example, considered amazing the ability of a snail to reproduce a head and the ability of a salamander to restore eyes, tail and legs exactly in those places where they were cut off.
The extent of damage and subsequent recovery varies widely. An extreme option is to restore the whole organism from a separate small part of it, actually from a group of somatic cells. Among animals, such restoration is possible in sponges and coelenterates. Among plants, the development of a whole new plant is possible even from one somatic cell, as was obtained with the example of carrots and tobacco. This type of restoration processes is accompanied by the emergence of a new morphogenetic axis of the body and is called B.P. Tokin “somatic embryogenesis”, for in many ways it resembles embryonic development.
There are examples of restoration of large areas of the body consisting of a complex of organs. Examples include the regeneration of the oral end in the hydra, the cephalic end in the annelid, and the restoration of the starfish from a single ray (Fig. 8.24). Regeneration of individual organs is widespread, for example, the limbs of a newt, the tail of a lizard, and the eyes of arthropods. Healing of skin, wounds, damage to bones and other internal organs is a less extensive process, but no less important for restoring the structural and functional integrity of the body. Of particular interest is the ability of embryos at early stages of development to recover after significant loss of material. This ability was the last argument in the struggle between supporters of preformationism and epigenesis and led G. Driesch to the concept of embryonic regulation in 1908.
Rice. 8.24. Regeneration of a complex of organs in some species of invertebrate animals. A - hydra; B - ringworm; IN - Starfish
(see text for explanation)
There are several varieties or methods of reparative regeneration. These include epimorphosis, morphallaxis, healing of epithelial wounds, regenerative hypertrophy, compensatory hypertrophy.
Epithelialization When healing wounds with damaged epithelial cover, the process is approximately the same, regardless of whether organ regeneration further occurs through epimorphosis or not. Epidermal wound healing in mammals, when the wound surface dries to form a crust, proceeds as follows (Fig. 8.25). The epithelium at the edge of the wound thickens due to an increase in cell volume and expansion of intercellular spaces. The fibrin clot plays the role of a substrate for the migration of the epidermis into the depths of the wound. Migrating epithelial cells do not undergo mitosis, but they have phagocytic activity. Cells from opposite edges come into contact. Then comes keratinization of the wound epidermis and separation of the crust covering the wound.
Rice. 8.25. Diagram of some of the events taking place
during epithelization of a skin wound in mammals.
A- the beginning of ingrowth of the epidermis under the necrotic tissue; B- fusion of the epidermis and separation of the scab:
1 -connective tissue, 2- epidermis, 3- scab, 4- necrotic tissue
By the time the epidermis meets opposite edges, a burst of mitosis is observed in the cells located immediately around the edge of the wound, which then gradually declines. According to one version, this outbreak is caused by a decrease in the concentration of the mitotic inhibitor - kaylon.
Epimorphosis is the most obvious method of regeneration, consisting in the growth of a new organ from the amputation surface. Limb regeneration of newts and axolotls has been studied in detail. There are regressive and progressive phases of regeneration. Regressive phase begin with healing wound, during which the following main events occur: stopping bleeding, contraction of the soft tissue of the limb stump, formation of a fibrin clot over the wound surface and migration of the epidermis covering the amputation surface.
Then it begins destruction osteocytes at the distal end of the bone and other cells. At the same time, cells involved in the inflammatory process penetrate into the destroyed soft tissues, phagocytosis and local edema are observed. Then, instead of forming a dense plexus of connective tissue fibers, as occurs during wound healing in mammals, differentiated tissue is lost in the area under the wound epidermis. Characterized by osteoclastic bone erosion, which is a histological sign dedifferentiation. The wound epidermis, already penetrated by regenerating nerve fibers, begins to quickly thicken. The spaces between tissues are increasingly filled with mesenchymal-like cells. The accumulation of mesenchymal cells under the wound epidermis is the main indicator of the formation of regenerative blastemas. The blastema cells look the same, but it is at this moment that the main features of the regenerating limb are laid down.
Then it begins progressive phase, which is most characterized by the processes of growth and morphogenesis. The length and weight of the regenerative blastema rapidly increase. The growth of the blastema occurs against the background of the formation of limb features in full swing, i.e. its morphogenesis. When the general shape of the limb has already developed, the regenerate is still smaller than the normal limb. The larger the animal, the greater this difference in size. The completion of morphogenesis requires time, after which the regenerate reaches the size of a normal limb.
Some stages of forelimb regeneration in a newt after amputation at the shoulder level are shown in Fig. 8.26. The time required for complete limb regeneration varies depending on the size and age of the animal, as well as the temperature at which it occurs.
Rice. 8.26. Stages of forelimb regeneration in newt
In young axolotl larvae, a limb can regenerate in 3 weeks, in adult newts and axolotls in 1-2 months, and in terrestrial ambistos this takes about 1 year.
During epimorphic regeneration, an exact copy of the removed structure is not always formed. This regeneration is called atypical. There are many types of atypical regeneration. Hypomorphosis - regeneration with partial replacement of the amputated structure. Thus, in an adult clawed frog, an awl-like structure appears instead of a limb. Heteromorphosis - the appearance of another structure in place of the lost one. This can manifest itself in the form of homeotic regeneration, which consists in the appearance of a limb in place of the antennae or eyes in arthropods, as well as in a change in the polarity of the structure. From a short fragment of planaria, a bipolar planaria can be reliably obtained (Fig. 8.27).
Formation of additional structures occurs, or excessive regeneration. After cutting the stump when amputating the head section of the planarian, regeneration of two or more heads occurs (Fig. 8.28). It is possible to obtain more digits when regenerating an axolotl limb by rotating the end of the limb stump 180°. Additional structures are mirror images of the original or regenerated structures next to which they are located (Bateson's law).
Rice. 8.27. Bipolar planaria
Morphallaxis - This is regeneration by restructuring the regenerating area. An example is the regeneration of a hydra from a ring cut from the middle of its body, or the restoration of a planaria from one tenth or twentieth of its part. In this case, no significant shaping processes occur on the wound surface. The cut piece shrinks, the cells inside it rearrange, and a whole individual appears
reduced in size, which then grows. This method of regeneration was first described by T. Morgan in 1900. In accordance with his description, morphallaxis occurs without mitosis. There is often a combination of epimorphic growth at the amputation site with reorganization through morphallaxis in adjacent parts of the body.
Rice. 8.28. Multi-headed planaria obtained after head amputation
and applying notches to the stump
Regenerative hypertrophy refers to internal organs. This method of regeneration involves increasing the size of the remaining organ without restoring its original shape. An illustration is the regeneration of the liver of vertebrates, including mammals. With a marginal injury to the liver, the removed part of the organ is never restored. The wound surface is healing. At the same time, cell proliferation (hyperplasia) increases inside the remaining part, and within two weeks after removal of 2/3 of the liver, the original weight and volume are restored, but not the shape. The internal structure of the liver appears to be normal, the lobules have a typical size. Liver function also returns to normal.
Compensatory hypertrophy consists of changes in one of the organs with a violation in another, belonging to the same organ system. An example is hypertrophy in one of the kidneys when the other is removed or enlargement of the lymph nodes when the spleen is removed.
The last two methods differ in the location of regeneration, but their mechanisms are the same: hyperplasia and hypertrophy.
Restoration of individual mesodermal tissues, such as muscle and skeletal tissue, is called tissue regeneration. For muscle regeneration, it is important to preserve at least small stumps at both ends, and for bone regeneration, periosteum is necessary. Regeneration by induction occurs in certain mesodermal tissues of mammals in response to the action of specific inducers that are introduced into the damaged area. This method makes it possible to completely replace the defect of the skull bones after introducing bone filings into it.
Thus, there are many different methods or types of morphogenetic phenomena in the restoration of lost and damaged parts of the body. The differences between them are not always obvious, and a deeper understanding of these processes is required.
The study of regeneration phenomena concerns not only external manifestations. There are a number of issues that are problematic and theoretical in nature. These include issues of regulation and conditions in which restoration processes occur, issues of the origin of cells involved in regeneration, the ability to regenerate in various groups, animals, and the characteristics of restoration processes in mammals.
It has been established that real changes in electrical activity occur in the limbs of amphibians after amputation and during the process of regeneration. When an electric current is passed through an amputated limb, adult clawed frogs exhibit increased forelimb regeneration. In the regenerates, the amount of nervous tissue increases, from which it is concluded that the electric current stimulates the ingrowth of nerves into the edges of the limbs, which do not normally regenerate.
Attempts to stimulate limb regeneration in mammals in a similar way have been unsuccessful. Thus, under the influence of an electric current or by combining the action of an electric current with a nerve growth factor, it was possible to obtain in rats only the growth of skeletal tissue in the form of cartilaginous and bone calluses, which did not resemble normal elements of the skeleton of the limbs.
There is no doubt that regeneration processes are regulated by nervous system. When the limb is thoroughly denervated during amputation, epimorphic regeneration is completely suppressed and a blastema never forms. Interesting experiments were carried out. If the nerve of a newt's limb is retracted under the skin of the base of the limb, an additional limb is formed. If it is taken to the base of the tail, the formation of an additional tail is stimulated. Reduction of the nerve to the lateral region does not cause any additional structures. These experiments led to the creation of the concept regeneration fields. .
It was found that the number of nerve fibers is decisive for the initiation of regeneration. The type of nerve does not matter. The influence of nerves on regeneration is associated with the trophic effect of nerves on the tissues of the limbs.
Data received in favor humoral regulation regeneration processes. A particularly common model to study this is the regenerating liver. After administration of serum or blood plasma from animals that had undergone liver removal to normal intact animals, stimulation of the mitotic activity of liver cells was observed in the former. In contrast, when injured animals were given serum from healthy animals, a decrease in the number of mitoses in the damaged liver was obtained. These experiments may indicate both the presence of regeneration stimulators in the blood of injured animals and the presence of cell division inhibitors in the blood of intact animals. Explaining the results of the experiments is complicated by the need to take into account the immunological effect of the injections.
The most important component of the humoral regulation of compensatory and regenerative hypertrophy is immunological response. Not only partial removal of an organ, but also many influences cause disturbances in the immune status of the body, the appearance of autoantibodies and stimulation of cell proliferation processes.
There is great disagreement on the issue of cellular sources regeneration. Where do undifferentiated blastema cells, morphologically similar to mesenchymal cells, come from or how do they arise? There are three assumptions.
1. Hypothesis reserve cells implies that the precursors of the regenerative blastema are the so-called reserve cells, which stop at some early stage of their differentiation and do not participate in the development process until they receive a stimulus for regeneration.
2. Hypothesis temporary dedifferentiation, or modulation of cells suggests that in response to a regenerative stimulus, differentiated cells can lose signs of specialization, but then differentiate again into the same cell type, i.e., having temporarily lost specialization, they do not lose determination.
3. Hypothesis complete dedifferentiation specialized cells to a state similar to mesenchymal cells and with possible subsequent transdifferentiation or metaplasia, i.e. transformation into cells of another type, believes that in this case the cell loses not only specialization, but also determination.
Modern research methods do not allow us to prove all three assumptions with absolute certainty. However, it is absolutely true that in the stumps of the axolotl digits, chondrocytes are released from the surrounding matrix and migrate into the regenerative blastema. Their further fate is not determined. Most researchers recognize dedifferentiation and metaplasia during lens regeneration in amphibians. The theoretical significance of this problem lies in the assumption of the possibility or impossibility of a cell changing its program to such an extent that it returns to a state where it is again able to divide and reprogram its synthetic apparatus. For example, a chondrocyte becomes a myocyte or vice versa.
The ability to regenerate does not have a clear dependence on organization level, although it has long been noticed that lower organized animals have a better ability to regenerate external organs. This is confirmed by amazing examples of regeneration of hydra, planarians, annelids, arthropods, echinoderms, and lower chordates, such as ascidians. Among vertebrates, tailed amphibians have the best regenerative ability. It is known that different species of the same class can differ greatly in their ability to regenerate. In addition, when studying the ability to regenerate internal organs, it turned out that it is significantly higher in warm-blooded animals, such as mammals, compared to amphibians.
Regeneration mammals is unique. For the regeneration of some external organs, special conditions are required. The tongue and ear, for example, do not regenerate with marginal damage. If you apply a through defect through the entire thickness of the organ, recovery goes well. In some cases, nipple regeneration was observed even after amputation at the base. Regeneration of internal organs can be very active. An entire organ is restored from a small fragment of the ovary. The features of liver regeneration have already been discussed above. Various mammalian tissues also regenerate well. There is an assumption that the impossibility of regeneration of limbs and other external organs in mammals is adaptive in nature and is due to selection, since with an active lifestyle, delicate morphogenetic processes would make existence difficult. Achievements of biology in the field of regeneration are successfully applied in medicine. However, there are many unresolved issues in the regeneration problem.
REGENERATION
restoration by the body of lost parts at one or another stage of the life cycle. Regeneration usually occurs in the event of damage or loss of an organ or part of the body. However, in addition to this, restoration and renewal processes constantly occur in every organism throughout its life. In humans, for example, the outer layer of skin is constantly renewed. Birds periodically shed their feathers and grow new ones, and mammals change their fur. Deciduous trees lose leaves every year and are replaced with fresh ones. Such regeneration, usually not associated with damage or loss, is called physiological. Regeneration that occurs after damage or loss of any part of the body is called reparative. Here we will consider only reparative regeneration. Reparative regeneration can be typical or atypical. In typical regeneration, the lost part is replaced by the development of exactly the same part. The cause of the loss may be an external force (for example, amputation), or the animal may deliberately tear off part of its body (autotomy), like a lizard breaking off part of its tail to escape an enemy. With atypical regeneration, the lost part is replaced by a structure that differs from the original quantitatively or qualitatively. The regenerated limb of a tadpole may have fewer fingers than the original one, and a shrimp may grow an antenna instead of an amputated eye.
REGENERATION IN ANIMALS
The ability to regenerate is widespread among animals. Generally speaking, lower animals are more often capable of regeneration than more complex, highly organized forms. Thus, among invertebrates there are many more species capable of restoring lost organs than among vertebrates, but only in some of them is it possible to regenerate an entire individual from a small fragment. Nevertheless, the general rule that the ability to regenerate decreases with increasing complexity of the organism cannot be considered absolute. Such primitive animals as ctenophores and rotifers are practically incapable of regeneration, but in much more complex crustaceans and amphibians this ability is well expressed; Other exceptions are known.
The tapeworm, which is many times longer than it is wide, can recreate an entire individual from any part of its body. It is theoretically possible, by cutting one worm into 200,000 pieces, to obtain 200,000 new worms from it as a result of regeneration. From one ray of a starfish, an entire star can regenerate.
Mollusks, arthropods and vertebrates are not able to regenerate a whole individual from one fragment, however, in many of them the lost organ is restored. Some resort to autotomy if necessary. Birds and mammals, as the most evolutionarily advanced animals, are less capable of regeneration than others. In birds, it is possible to replace feathers and some parts of the beak. Mammals can restore their integument, claws, and partly their liver; they are also capable of healing wounds, and deer are capable of growing new antlers to replace those shed.
Regeneration processes. Two processes are involved in regeneration in animals: epimorphosis and morphallaxis. In epimorphic regeneration, the lost part of the body is restored due to the activity of undifferentiated cells. These embryonic-like cells accumulate under the wounded epidermis at the cut surface, where they form the primordium, or blastema. Blastema cells gradually multiply and transform into the tissue of a new organ or body part. In morphallaxis, other tissues of the body or organ are directly transformed into the structures of the missing part. In hydroid polyps, regeneration occurs mainly through morphallaxis, while in planarians both epimorphosis and morphallaxis are simultaneously involved in it. Regeneration by blastema formation is widespread in invertebrates and plays a particularly important role in organ regeneration in amphibians. There are two theories of the origin of blastema cells: 1) blastema cells originate from “reserve cells”, i.e. cells that remained unused during embryonic development and were distributed among different organs of the body; 2) tissues, the integrity of which was violated during amputation, “dedifferentiate” in the area of the incision, i.e. disintegrate and transform into individual blastema cells. Thus, according to the “reserve cell” theory, the blastema is formed from cells that remained embryonic, which migrate from different parts of the body and accumulate near the cut surface, and according to the “dedifferentiated tissue” theory, blastema cells originate from cells of damaged tissues. There is enough data to support both one and the other theory. For example, in planarians, reserve cells are more sensitive to X-rays than cells of differentiated tissue; therefore, they can be destroyed by strictly dosing radiation so as not to damage normal planarian tissue. Individuals irradiated in this way survive, but lose their ability to regenerate. However, if only the anterior half of the planarian body is irradiated and then cut, then regeneration occurs, although with some delay. The delay indicates that the blastema is formed from reserve cells migrating to the cut surface from the non-irradiated half of the body. The migration of these reserve cells throughout the irradiated part of the body can be observed under a microscope. Similar experiments showed that in the newt, limb regeneration occurs due to blastema cells of local origin, i.e. due to dedifferentiation of damaged stump tissues. If, for example, you irradiate the entire newt larva except, say, the right forelimb, and then amputate that limb at the level of the forearm, the animal will grow a new forelimb. It is obvious that the blastema cells necessary for this come precisely from the stump of the forelimb, since the rest of the body has been irradiated. Moreover, regeneration occurs even if the entire larva is irradiated, with the exception of a 1 mm wide area on the right fore tarsus, and then the latter is amputated by making an incision through this non-irradiated area. In this case, it is quite clear that the blastema cells come from the cut surface, since the entire body, including the right foreleg, was deprived of the ability to regenerate. The described processes were analyzed using modern methods. An electron microscope allows you to observe changes in damaged and regenerating tissues in all details. Dyes have been created that reveal certain chemicals contained in cells and tissues. Histochemical methods (using dyes) make it possible to judge the biochemical processes occurring during the regeneration of organs and tissues.
Polarity. One of the most mysterious problems in biology is the origin of polarity in organisms. From the spherical egg of a frog, a tadpole develops, which from the very beginning has a head with a brain, eyes and mouth at one end of the body, and a tail at the other. Similarly, if you cut the body of a planarian into individual fragments, a head develops at one end of each fragment and a tail at the other. In this case, the head is always formed at the anterior end of the fragment. Experiments clearly show that the planarian has a gradient of metabolic (biochemical) activity along the anterior-posterior axis of its body; in this case, the highest activity is at the very anterior end of the body, and towards the posterior end the activity gradually decreases. In any animal, the head is always formed at the end of the fragment where metabolic activity is higher. If the direction of the gradient of metabolic activity in an isolated fragment of planaria is reversed, then the formation of the head will occur at the opposite end of the fragment. The gradient of metabolic activity in the body of planarians reflects the existence of some more important physicochemical gradient, the nature of which is still unknown. In the regenerating limb of a newt, the polarity of the newly formed structure appears to be determined by the preserved stump. For reasons that still remain unclear, only structures located distal to the wound surface are formed in the regenerating organ, and those located more proximally (closer to the body) never regenerate. So, if the hand of a newt is amputated, and the remaining part of the forelimb is inserted with the cut end into the body wall and this distal (distant from the body) end is allowed to take root in a new, unusual place for it, then the subsequent transection of this upper limb near the shoulder (freeing it from the connection with the shoulder) leads to the regeneration of the limb with a full set of distal structures. At the time of cutting, such a limb has the following parts (starting from the wrist, fused with the body wall): wrist, forearm, elbow and distal half of the shoulder; then, as a result of regeneration, the following appear: another distal half of the shoulder, elbow, forearm, wrist and hand. Thus, the inverted (upside down) limb regenerated all parts located distal to the wound surface. This striking phenomenon indicates that the tissues of the stump (in this case the limb stump) control the regeneration of the organ. The task of further research is to find out exactly what factors control this process, what stimulates regeneration and what causes the cells that ensure regeneration to accumulate on the wound surface. Some scientists believe that damaged tissue releases some kind of chemical "wound factor." However, it has not yet been possible to isolate a chemical substance specific to wounds.
REGENERATION IN PLANTS
The widespread occurrence of regeneration in the plant kingdom is due to the preservation of meristems (tissues consisting of dividing cells) and undifferentiated tissues. In most cases, regeneration in plants is, in essence, one of the forms of vegetative propagation. Thus, at the tip of a normal stem there is an apical bud, which ensures the continuous formation of new leaves and the growth of the stem in length throughout the life of the plant. If this bud is cut off and kept moist, new roots often develop from the parenchyma cells present in it or from the callus formed on the surface of the cut; the bud continues to grow and gives rise to a new plant. The same thing happens in nature when a branch breaks off. The lashes and stolons are separated as a result of the death of old sections (internodes). In the same way, the rhizomes of iris, wolf's foot or ferns are divided, forming new plants. Typically, tubers, such as potato tubers, continue to live after the underground stem on which they grew has died; with the onset of a new growing season, they can give rise to their own roots and shoots. In bulbous plants, such as hyacinths or tulips, shoots form at the base of the bulb scales and can in turn form new bulbs, which eventually produce roots and flowering stems, i.e. become independent plants. In some lilies, aerial bulbs form in the axils of the leaves, and in a number of ferns, brood buds grow on the leaves; at some point they fall to the ground and resume growth. Roots are less capable of forming new parts than stems. For this, the dahlia tuber needs a bud that forms at the base of the stem; however, sweet potatoes can give rise to a new plant from a bud formed by a root cone. Leaves are also capable of regeneration. In some species of ferns, for example, in the fern (Camptosorus), the leaves are very elongated and look like long hair-like structures ending in a meristem. From this meristem the embryo develops with rudimentary stem, roots and leaves; if the tip of the parent plant's leaf bends down and touches the soil or moss, the bud begins to grow. The new plant separates from the parent after the depletion of this hair-like formation. The leaves of the succulent houseplant Kalanchoe bear well-developed plantlets at the edges that fall off easily. New shoots and roots form on the surface of begonia leaves. Special bodies called embryonic buds develop on the leaves of some club mosses (Lycopodium) and liverworts (Marchantia); falling to the ground, they take root and form new mature plants. Many algae reproduce successfully by breaking into fragments under the impact of waves.
see also PLANT SYSTEMATICS. LITERATURE Mattson P. Regeneration - present and future. M., 1982 Gilbert S. Developmental biology, vol. 1-3. M., 1993-1995
Collier's Encyclopedia. - Open Society. 2000 .
Synonyms:See what "REGENERATION" is in other dictionaries:
REGENERATION- REGENERATION, the process of formation of a new organ or tissue in place of a part of the body that was removed in one way or another. Very often R. is defined as the process of restoring what has been lost, that is, the formation of an organ similar to the removed one. This... ... Great Medical Encyclopedia
- (late lat., from lat. re again, again, and genus, eris genus, generation). Revival, renewal, restoration of what was destroyed. In a figurative sense: a change for the better. Dictionary of foreign words included in the Russian language.... ... Dictionary of foreign words of the Russian language
REGENERATION, in biology, the body’s ability to replace one of the lost parts. The term regeneration also refers to a form of Asexual Reproduction in which a new individual arises from a separated part of the mother's body... Scientific and technical encyclopedic dictionary
Restoration, recovery; compensation, regeneration, renewal, heteromorphosis, pettencoferation, revival, morphallaxis Dictionary of Russian synonyms. regeneration noun, number of synonyms: 11 compensation (20) ... Synonym dictionary
1) restoration, using certain physicochemical processes, of the original composition and properties of waste products for their reuse. In military affairs, air regeneration has become widespread (especially on underwater... ... Marine Dictionary
Regeneration- – returning the used product to its original properties. [Terminological dictionary of concrete and reinforced concrete. FSUE "Research Center "Construction" NIIZHB named after. A. A. Gvozdeva, Moscow, 2007, 110 pp.] Regeneration - restoration of waste... ... Encyclopedia of terms, definitions and explanations of building materials
REGENERATION- (1) restoration of the original properties and composition of waste materials (water, air, oils, rubber, etc.) for their reuse. It is carried out with the help of certain physical chem. processes in special regenerator devices. Wide... ... Big Polytechnic Encyclopedia
- (from Late Lat. regeneratio rebirth renewal), in biology, the restoration by the body of lost or damaged organs and tissues, as well as the restoration of the whole organism from its part. Mostly characteristic of plants and invertebrates... ...
In technology, 1) returning the spent product to its original qualities, for example. restoration of the properties of spent molding sand in foundries, purification of used lubricating oil, transformation of worn rubber products into plastic... ... Big Encyclopedic Dictionary
REGENERATION, regeneration, many. no, female (lat. regeneratio restoration, return). 1. Heating of gas and air entering the furnace with waste combustion products (technical). 2. Reproduction of lost organs by animals (zool.). 3. Radiation... ... Ushakov's Explanatory Dictionary
