Regeneration processes are going on. Successes of modern natural science

. REGENERATRON

. ARTIFICIAL ORGANS

Definition of "REGENERATION"

Regeneration- the process of restoration by the body of lost or damaged structures. Regeneration maintains the structure and functions of the body, its integrity.

Vladimir Nikitich Yarygin, (1942-2013), Soviet and Russian biologist, academician of the Russian Academy of Medical Sciences, Doctor of Medical Sciences, professor, member of the Presidium of the Russian Academy of Medical Sciences

The main ideologist of regenerative medicine in Russia.

Regeneration- replacement of various structures (from parts of cells to large parts of the body) after natural wear or accidental loss.

Bruce M. Carlson, Professor Emeritus of Anatomy and Cell Biology at Michigan State University

He previously served as Chair of the Department of Anatomy and Cell Biology at the School of Medicine and was also Director of the Institute of Gerontology.

Regeneration- the process of secondary development of organs caused by damage of one kind or another.

Vorontsova Maria Alexandrovna (1902-1956), professor, doctor of biological sciences, head of the laboratory of growth and development of the Institute of Experimental Biology of the USSR Academy of Medical Sciences

She laid the foundation for the study in the USSR of the regeneration of internal organs in mammals. Created a regulatory theory individual development organism.

Galina Pavlovna Korotkova (1925-2012), embryologist, Doctor of Biological Sciences, Professor of the Department of Embryology of St. Petersburg state university

Regeneration is a restorative morphogenesis (development), which always has a multilevel character and varies in its mechanisms depending on the specifics, degree and localization of damage, as well as on the stage of individual development and the complexity of the organization of an individual or colony.

Lev Vladimirovich Polezhaev (1910-2000), biologist, doctor of biological sciences, professor, chief researcher-consultant of the Institute of General Genetics of the Russian Academy of Sciences

Regeneration is the phenomenon of restoration of the lost part of the body - an organ, tissue or cell. During regeneration, the form and structure are always restored, but not always the function of the organ.

He observed the processes of regeneration in worms, hydras, starfish, snails, crayfish, amphibians. He argued that regeneration is one of the forms of adaptation of some animal species to adverse effects. external environment. As a rule, it is best to regenerate organs that are more likely to be lost in natural conditions.

One of the unique adaptive reactions is the ability of organs to autotomy. Autotomy - separation from the body and the rejection by the animal of any of its organs. Autotomy serves to protect the animal from attack: by losing a separate organ or part of it, the animal saves its life. Lost organs are often restored.

So, for example, the most famous example is a lizard running away from a predator and discarding its tail.

Detachment of the tail is a very difficult method of protection. The separation process itself directly depends on the size of the lizard. Large and slow animals shed more of their tail than small and fast species. Tail throwing is controlled by the hemispheres of the brain, and the lizard is able to decide for itself when to do so. Most tails have transverse tear zones on the spinal cartilage, muscles, and ligaments. In case of danger, when the lizard is grabbed by the tail, the circular muscles in this zone contract and tear. At the same time, the muscles not only tear the tail, but also immediately tighten the blood vessels, preventing blood loss. When the tail is dropped, a convulsive automatic contraction of the muscles occurs. The tail bounces to the side, distracting the predator.

In addition to autotomy of the tail, some lizards, in particular skink geckos, can also have a much less known process - autotomy. skin. The seized lizard begins to rapidly rotate around the axis of the body, while the flap of skin in those places for which it was seized is easily torn off, and the animal runs away. Interestingly, in this case, there is almost no bleeding, and the lost skin is soon restored without scarring.

It is little known that some species of snakes (striped snake, northern snake, brown snake, Florida snake, rhombic snake, common garter snake, eastern ribbon snake, western pig-nosed snake, Asian striped snake, angler snake, antilofis) can also throw off their tails. The tail, like that of a lizard, begins to wriggle and jump convulsively. In snakes, the tail grows quite quickly, it takes about 4 months, and the tail regenerate in size and color practically does not differ from the discarded one.

Octopuses are unique animals that can reach large sizes, for example, Doflein's giant octopus reaches a length of 960 cm and a mass of up to 270 kg. Have quite big brain, the intelligence of an octopus is comparable to that of a domestic cat. He possesses, sense of smell, emotions and has a good memory. An octopus, in order to save life, with a sharp contraction of muscles (the muscles of the tentacle at this moment begin to spasmodically contract and tear) can tear off its tentacle, leaving it to the enemy. The wound heals within a few days, and the limb, which sometimes exceeds several meters in length, is able to grow back. Moreover, the octopus can tear off the tentacle anywhere at its discretion.

Some species of echinoderms have a unique kind of autotomy - evisceration. For example, their representative is holothuria, or sea cucumber (species eaten are common name"trepang"), in response to strong irritation, spontaneously throw some of their internal organs outward (through the anus or mouth opening) partially or entirely: the intestine, water lungs or Cuvier's organs, in the form of long hollow threads (the purpose of the latter has not yet been fully clarified).

It should be noted that the body length of holothurians varies from 3 cm to 1-2 meters, although one of their species, Synaptamaculata, can reach 5 m. All discarded organs grow back after some time.

A team of biologists led by Ashley Seyfert found that African spiny mice of the species Acomyskempi and Acomyspercivali are able to shed their skin when escaping from a predator and have the unique ability to regenerate it.

Ashley W. Seifert Assistant Professor, Department of Biology, University of Kentucky, USA. http://www.
ashleyseifert.com

American scientists investigated the mechanical properties of the skin of these mice. It turned out that the skin of spiny mice was very fragile - it withstands stretching 20 times worse than the skin of ordinary mice, and was torn at 77 times less force. At the same time, there were no zones with relatively low or high skin strength on the body of mice - the skin was easily torn off at any point of the body. The high fragility of the skin of these unique mice is compensated by the amazing ability to regenerate it. Wounds are overgrown with new skin with full hair follicles and other components without scars, and this newly formed skin is no different in its structure from normal. To test this ability of their wards, scientists conducted another experiment - they cut out auricle mice have a through hole and followed its recovery. To the surprise of the biologists, all ear tissues, except for the muscle tissue, successfully recovered.

A variation of autotomy is the shedding of antlers in deer, deer and elk. One of the main reasons for the absence of noticeable manifestations of the regenerative capacity in mammals is considered to be their “highly organized nature”. However, the regeneration of the horns renders such an assumption completely untenable. The horns are a rather complexly organized organ, resembling the structure of the limbs. The basis of the horns of this group of animals is a spongy bone covered with skin with short thick hair ("velveteen"), the horns are pierced by large blood vessels. The growth of the horns is striking in its speed. For example, in red deer (Cervuselaphus), it can reach 1 cm per day. And in larger deer, antler growth is even faster. Moose, the largest members of the family, have antlers that can reach 129.5 centimeters in length and grow at a rate of 2.75 centimeters per day.

The growth of new antlers in moose in the south begins in April, in the north - in May and lasts 2-2.5 months until the end of June - beginning of July. The weight of a pair of horns in large bull moose can reach 30 kg, the distance between the extreme processes is up to 1.5 m. This phenomenon of organ regeneration demonstrates the absolute inconsistency of the assertion that large body parts either cannot regenerate at all, or it will take too long.

Regeneration (recovery) - the ability of living organisms to restore damaged tissues over time, and sometimes entire lost organs. Regeneration is also called the restoration of a whole organism from its artificially separated fragment (for example, the restoration of a hydra from a small fragment of the body or dissociated cells). In protists, regeneration can manifest itself in the restoration of lost organelles or cell parts.

It happens physiological and reparative. Regeneration in the course of the normal life of the organism, usually not associated with damage or loss, is called physiological. In every organism, throughout its life, processes of restoration and renewal are constantly going on. In humans, for example, is constantly updated outer layer skin. Birds periodically shed feathers and grow new ones, and mammals change their coat. In deciduous trees, the leaves fall annually and are replaced by fresh ones.

An example of physiological regeneration at the intracellular level are 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. First of all, this refers to the nervous tissue.

Examples of physiological regeneration at the cellular tissue level are the renewal of the epidermis of the skin, the cornea of ​​the eye, the epithelium of the intestinal mucosa, peripheral blood cells, and others. The derivatives of the epidermis are updated - hair and nails. This so-called proliferative regeneration, i.e. replenishment of the number of cells due to their division.

Regeneration. Types of regeneration. Reparative regeneration, its significance. Methods of reparative regeneration (epimorphosis, morpholaxis). Homomorphosis, hypomorphosis, heteromorphosis, hypermorphosis. Examples.

Reparative refers to the regeneration that occurs after damage or loss of any part of the body. Allocate typical and atypical reparative regeneration.

In typical regeneration, the lost part is replaced by the development of exactly the same part. The reason for the loss may be external influence(for example, amputation), or the animal deliberately tears off part of its body (autotomy), like a lizard breaking off part of its tail to escape from the enemy.

In atypical regeneration, the lost part is replaced by a structure that differs quantitatively or qualitatively from the original. In a regenerated tadpole limb, the number of fingers may be less than the original, and in a shrimp, instead of an amputated eye, an antenna may grow.

Epimorphosis - a variant of the process of organ regeneration with the loss of part of the organ, characterized, in contrast to morphallaxis, by the regrowth of the missing part of the organ without changing the shape and size of the remaining part of the organ.

Morphallaxis (from the Greek morphe - appearance, form and allaxis - change), one of the methods of regeneration in animals, in which the formation of a whole organism or its organ from a part of the body or organ remaining after damage occurs by restructuring this area (cf. Epimorphosis). M. is observed in many coelenterates, flat and annelids, arthropods, and also in tunicates.

Homomorphosis (complete regeneration, restitution) is the completion of the process of regeneration of a removed organ by restoring an organ identical in shape, size and functionality.

Heteromorphosis (incomplete regeneration, restitution) - completion of the process of regeneration of a removed organ by restoring an organ that differs from the original in functionality (formation of another organ).

Hypermorphosis (from hyper ... and Greek morphe - appearance, form), hyperthelia, superspecialization, type of phylogenetic development, leading to disruption of the body's relationship with the environment due to hypertrophy of individual organs (for example, fangs of a fossil saber-toothed tiger - mahairod, horns of a giant deer , fangs of a modern wild boar - babirus, etc.). special case G. - a general increase in body size, leading to a violation of the correlations of individual organs

Regeneration. Types of regeneration. reparative regeneration. Morpholaxis. Endomorphosis (regenerative hypertrophy, compensatory hypertrophy). Examples. Manifestation of regenerative capacity in phylogenesis. Application in medicine. Factors affecting the regeneration process.

Endomorphosis is a restoration that takes place inside the organ. At the same time, it is not the shape that is restored, but the mass of the organ.

Regenerative hypertrophy refers to internal organs. This method of regeneration consists in increasing the size of the remnant of the organ without restoring the 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 heals. At the same time, cell proliferation (hyperplasia) intensifies inside the remaining part, and within two weeks after the removal of 2/3 of the liver, the original mass and volume are restored, but not the shape. The internal structure of the liver is normal, the lobules have a typical size for them. Liver function also returns to normal.
Compensatory hypertrophy consists in changes in one of the organs with a violation in another, related to the same organ system. An example is hypertrophy in one of the kidneys when another is removed, or an increase in lymph nodes when the spleen is removed.

Regeneration in medicine. There are physiological, reparative and pathological regeneration. For injuries etc. pathological conditions, which are accompanied by massive cell death, tissue restoration is carried out due to reparative (restorative) regeneration. If in the process of reparative regeneration the lost part is replaced by an equivalent, specialized tissue, they speak of complete regeneration (restitution); if unspecialized connective tissue grows at the site of the defect, it is about incomplete regeneration (healing through scarring). In some cases, during substitution, the function is restored due to the intensive neoplasm of tissue (similar to the deceased) in the intact part of the organ. This neoplasm occurs either through increased cell reproduction, or due to intracellular regeneration - restoration of subcellular structures with an unchanged number of cells (heart muscle, nervous tissue). Age, metabolic characteristics, state of the nervous and endocrine systems, nutrition, intensity of blood circulation in the damaged tissue, concomitant diseases can weaken, enhance or qualitatively change the regeneration process. In some cases, this leads to pathological regeneration. Its manifestations: long-term non-healing ulcers, impaired healing of bone fractures, excessive tissue growth or the transition of one type of tissue to another. Healing effects on the process of regeneration are to stimulate complete and prevent pathological regeneration.

The process of regeneration depends not only on the level of organization of the animal, but also on many other factors and is therefore characterized by variability. The assertion that the ability to regenerate naturally decreases with age is also incorrect; it can also increase in the process of ontogenesis, but in the period of old age it often decreases. Over the last quarter of a century, it has been shown that, although entire external organs do not regenerate in mammals and humans, their internal organs, as well as muscles, skeleton, skin, are capable of regeneration, which is studied at the organ, tissue, cellular and subcellular levels.

.71. Characteristics of transplantation. Types of transplantation - autotransplantation, allotransplantation, xenotransplantation. Ways to overcome tissue incompatibility. Significance for medicine.

Transplantation is the transplantation or engraftment of organs and tissues. The transplanted part of the organ is called a graft. the organism to which the graft is transplanted is the recipient.

There are autotransplantation, when transplantation is carried out on another part of the body of the same organism, allotransplantation, when transplantation is performed from one individual to another belonging to the same species, and xenotransplantation, when the donor and recipient belong to different species.

Transplantation in medical practice.

In those cases when the organ cannot be regenerated, but it is necessary, there is only one method left - to replace it with the same natural or artificial organ.

In plastic surgeries performed to restore the shape and function of any organ or deformed surface of the body, transplantation of skin, cartilage, muscles, tendons, blood vessels, nerves, omentum is common. and chest walls, skull, are also plastic.

Припластическихоперацияхпользуютсяпреимущественноаутотрансплантацией.Длятогочтобытрансплантатприжился, необходимообеспечитьегопитанием на новомместе.С этойцельюдляпересадкикожибылразработанметодкруглогостебля, обеспечивающийпитаниекожноголоскута на старомместе.Такжебылсозданметодпересадкироговицы, взятойоттрупа, с цельюлеченияслепоты, вызваннойповреждениями и язвами на роговице.Благодаряоперациям, проведеннымпоэтомуметоду, возвращенозрениемногимтысячамлюдей.Пересадкароговицыпротекаетбезосложнений, которыесопровождаютпересадкудругихорганов, таккакроговицанесодержиткровеносныхкапилляров и, следовательно, в неёнепопадаютклеткииммуннойсистемыкрови.

Посколькуабсолютноточноподобратьдонора и реципиентаповсемантигенамневозможно, возникаетпроблемаподавленияиммуннойреакцииотторжения.Большоезначение в этомимеетявлениеиммунологическойтолерантности к чужероднымклеткам.Этоявлениебылооткрыто на разныхорганизмахнезависимодруготдруга.Иммуннаясистема, направленнаяпротивлюбыхгенетическичужеродныхвеществ и клеток, защищаеторганизмотмикробов и вирусов.Однакоэтосвойство, выработанное в процесседлительнойэволюции, обращаетсяпротив интереса человека в случаепересадкиорганов и тканей.В этомслучае, а такжеприаутоиммунныхзаболеваниях, передученымивсталазадачаподавленияиммунитета – иммунодепрессии. This is achieved in various ways: by suppressing the activity of the immune system, by irradiation, by the introduction of a special anti-lymphatic serum, hormones of the adrenal cortex.

Various chemical preparations - antidepressants are also used.

72. Explantation. Modern directions (use of stem cells, cloning)

Explantation is the cultivation of isolated organs and tissues.

The cultivation of isolated organs outside the body is based on the fact that in organs separated from the whole organism, under certain conditions, vital processes can be carried out.

Regeneration(recovery) - the ability of living organisms to restore damaged tissues over time, and sometimes entire lost organs. Regeneration is also called the restoration of a whole organism from its artificially separated fragment (for example, the restoration of a hydra from a small fragment of the body or dissociated cells). In protists, regeneration can manifest itself in the restoration of lost organelles or cell parts.

Regeneration that occurs in case of damage or loss of any organ or part of the body is called reparative. Regeneration in the course of the normal life of an organism, usually not associated with damage or loss of a part of the organism, is called physiological.

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Physiological regeneration

In every organism, throughout its life, processes of restoration and renewal are constantly going on. In humans, for example, the outer layer of the skin is constantly updated. Birds periodically shed their feathers and grow new ones, while mammals change their coat. In deciduous trees, the leaves fall annually and are replaced by fresh ones. Such processes are called physiological regeneration.

Reparative regeneration

Reparative refers to the regeneration that occurs after damage or loss of any part of the body. Allocate typical and atypical reparative regeneration.

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 influence (for example, amputation), or the animal deliberately tears off part of its body (autotomy), like a lizard breaking off part of its tail to escape from the enemy.

In atypical regeneration, the lost part is replaced by a structure that differs quantitatively or qualitatively from the original. In a regenerated limb of a tadpole, the number of fingers may be less than the original, and in a shrimp, instead of an amputated eye, an antenna may grow (heteromorphosis).

Regeneration in animals

The ability to regenerate is widespread among animals. Lower animals, as a rule, are more often able to regenerate than more complex, highly organized forms. So, 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 of it. Nevertheless, the general rule about a decrease in the ability to regenerate with an increase in the complexity of the organism cannot be considered absolute. Such primitive animals as roundworms and rotifers are practically incapable of regeneration, and in much more complex crustaceans and amphibians this ability is well expressed; other exceptions are known. Some comparatively closely related animals differ greatly in this respect. So, in many species of earthworms, a new individual can completely regenerate only from the front half of the body, while leeches are not able to restore even individual lost organs. In tailed amphibians, a new limb is formed in place of the amputated limb, while in the frog, the stump simply heals and no new growth occurs. However, as Polezhaev's experiments showed, if the frog's stump is subjected to mechanical irritations or exposure to certain chemicals, the limb regenerates. Moreover, under such conditions, the limbs of some mammals, for example, newborn rat pups, also regenerate.

There is also no clear relationship between embryonic development and the ability to regenerate. Thus, in some animals with strictly determined development (comtenophores, polychaetes) in the adult state, regeneration is well developed (in crawling ctenophores and some polychaetes, a whole individual can recover from a small area of ​​the body), and in some animals with regulative development (sea   urchins, mammals) - weak enough.

Many invertebrates are capable of regenerating a significant portion of their body. In most species of sponges, hydroid polyps, many types of flat, tape and annelids, bryozoans, echinoderms and tunicates, a whole organism can regenerate from a small fragment of the body. Especially remarkable is the ability of sponges to regenerate. If the body of an adult sponge is pressed through a mesh tissue, then all the cells will separate from each other, as if sifted through a sieve. If you then place all these individual cells in water and carefully, thoroughly mix, completely destroying all the bonds between them, then after a while they begin to gradually approach each other and reunite, forming a whole sponge, similar to the previous one. A kind of "recognition" at the cellular level is involved in this, as evidenced by the following experiment: sponges of three different types were divided into separate cells in the described way and mixed properly. At the same time, it was found that cells of each species are able to “recognize” cells of their own species in the total mass and reunite only with them, so that as a result, not one, but three new sponges, similar to the three original ones, were formed. Of other animals, only hydra is capable of restoring a whole organism from a suspension of cells.

There is a lot of research being done on tooth regeneration. Researchers from Okayama University (Japan) were able to show successful functional restoration of teeth using regeneration in a large animal model in the postnatal period.

Regeneration in humans

In humans, the epidermis regenerates well, and its derivatives, such as hair and nails, are also capable of regeneration. Bone tissue also has the ability to regenerate (bones grow together after fractures). With the loss of part of the liver (up to 75%), the remaining fragments begin to increase in size due to an increase in the size of the cells themselves, but not due to an increase in their number. Thus, the liver completely restores its original mass. Can regenerate fingertips under certain conditions

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REGENERATION, restoration by the body of lost parts at one stage or another life cycle. Regeneration usually occurs when an organ or part of the body is damaged or lost. However, in addition to this, in every organism throughout its life, processes of restoration and renewal are constantly going on. In humans, for example, the outer layer of the skin is constantly updated. Birds periodically shed their feathers and grow new ones, while mammals change their coat. In deciduous trees, the leaves fall annually and are replaced by 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 may 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 influence (for example, amputation), or the animal deliberately tears off part of its body (autotomy), like a lizard breaking off part of its tail to escape from the enemy. In atypical regeneration, the lost part is replaced by a structure that differs quantitatively or qualitatively from the original. In a regenerated tadpole limb, the number of fingers may be less than the original, and in a shrimp, instead of an amputated eye, an antenna may grow.

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 its small fragment. Nevertheless, the general rule about a decrease in the ability to regenerate with an increase in the complexity of the organism cannot be considered absolute. Such primitive animals as ctenophores and rotifers are practically incapable of regeneration, while this ability is well expressed in much more complex crustaceans and amphibians; other exceptions are known. Some closely related animals differ greatly in this respect. So, in an earthworm, a new individual can completely regenerate from a small piece of the body, while leeches are unable to restore one lost organ. In tailed amphibians, a new limb is formed in place of the amputated limb, while in the frog, the stump simply heals and no new growth occurs.

Many invertebrates are capable of regenerating a significant portion of their body. In sponges, hydroid polyps, flat, tape and annelids, bryozoans, echinoderms and tunicates, a whole organism can regenerate from a small fragment of the body. Especially remarkable is the ability of sponges to regenerate. If the body of an adult sponge is pressed through a mesh tissue, then all the cells will separate from each other, as if sifted through a sieve. If you then place all these individual cells in water and carefully, thoroughly mix, completely destroying all the bonds between them, then after a while they begin to gradually approach each other and reunite, forming a whole sponge, similar to the previous one. This involves a kind of "recognition" at the cellular level, as evidenced by the following experiment. Sponges three different types divided by the described method into individual cells and mixed properly. At the same time, it was found that cells of each species are able to "recognize" cells of their own species in the total mass and reunite only with them, so that as a result, not one, but three new sponges, similar to the three original ones, were formed.

The tapeworm, which is many times longer than its width, is able to recreate a whole 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. A single starfish beam can regenerate an entire star.

Mollusks, arthropods, and vertebrates are not able to regenerate a whole individual from a single fragment, but many of them recover the lost organ. Some, if necessary, resort to autotomy. Birds and mammals, as evolutionarily the most advanced animals, are less capable of regeneration than others. In birds, the replacement of feathers and some parts of the beak is possible. Mammals can regenerate integument, claws, and partially 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. During epimorphic regeneration, the lost part of the body is restored due to the activity of undifferentiated cells. These embryonic-like cells accumulate under the injured epidermis at the surface of the incision, where they form the primordium, or blastema. Blastema cells gradually multiply and turn into tissues 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 by morphallaxis, while in planarians, both epimorphosis and morphallaxis are involved in it simultaneously.

Regeneration by blastema formation is widespread in invertebrates and plays a particularly important role in amphibian organ regeneration. There are two theories of the origin of blastema cells: 1) blastema cells originate from "reserve cells", i.e. cells left unused in the process of embryonic development and distributed over different bodies 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 theory of "reserve cells", the blastema is formed from cells that remained embryonic, which migrate from different parts of the body and accumulate at the surface of the cut, and according to the theory of "dedifferentiated tissue", blastema cells originate from cells of damaged tissues.

In support of both one and the other theory, there is enough data. For example, in planarians, reserve cells are more sensitive to x-rays than cells in differentiated tissue; therefore, they can be destroyed by strictly dosing radiation so as not to damage the normal tissues of the planarian. Individuals irradiated in this way survive, but lose the ability to regenerate. However, if only the front half of the body of a planarian is exposed to radiation and then cut, then regeneration occurs, albeit with some delay. The delay indicates that the blastema is formed from reserve cells migrating to the cut surface from the unirradiated half of the body. The migration of these reserve cells along the irradiated part of the body can be observed under a microscope.

Similar experiments have shown that in the newt limb regeneration occurs due to blastema cells of local origin; due to dedifferentiation of damaged stump tissues. If, for example, the entire newt larva is irradiated, with the exception of, say, the right forelimb, and then this limb is amputated at the level of the forearm, then a new forelimb grows in the animal. Obviously, the blastema cells necessary for this come 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, except for a 1 mm wide area on the right forepaw, and then the latter is amputated by making an incision through this unirradiated area. In this case, it is quite obvious that the blastema cells come from the cut surface, since the entire body, including the right forepaw, was deprived of the ability to regenerate.

The described processes were analyzed using modern methods. An electron microscope makes it possible 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 biochemical processes occurring during the regeneration of organs and tissues.

Polarity.

One of the most puzzling problems in biology is the origin of polarity in organisms. A tadpole develops from a spherical frog egg, 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 separate 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 front end of the fragment. Experiments clearly show that the planaria has a gradient of metabolic (biochemical) activity running along the anterior-posterior axis of its body; at the same time, the most anterior end of the body has the highest activity, and activity gradually decreases towards the posterior end. In any animal, the head is always formed at the end of the fragment, where the metabolic activity is higher. If the direction of the metabolic activity gradient in an isolated planarian fragment is reversed, then the head will also form 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 the newt, the polarity of the newly formed structure is apparently 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 that are located proximal (closer to the body) never regenerate. So, if the newt's hand 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 its connection with the shoulder) leads to the regeneration of the limb with a complete set of distal structures. Such a limb has the following parts at the time of transection (starting from the wrist, which has merged with the body wall): wrist, forearm, elbow and distal half of the shoulder; then, as a result of regeneration, appear: another distal half of the shoulder, elbow, forearm, wrist and hand. Thus, the inverted (inverted) limb regenerated all parts distal to the wound surface. This striking phenomenon indicates that the tissues of the stump (in this case, the stump of the limb) control the regeneration of the organ. Task further research– find out exactly what factors control this process, what stimulates regeneration and what causes the cells that provide 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 specific for wounds.

REGENERATION IN PLANTS

The widespread use 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. So, 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 this plant. If this bud is cut off and kept moist, new roots often develop from the parenchymal cells present in it or from the callus that forms on the cut surface; while the bud continues to grow and gives rise to a new plant. The same thing happens in nature when a branch breaks off. Scourges 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. Usually tubers, such as potato tubers, continue to live after the death of the underground stem on which they grew; 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 scales of the bulb and can in turn form new bulbs, which eventually give rise to roots and flowering stems, i.e. become independent plants. In some lilies, air 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, a 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, the hookworm ( Camptosorus), the leaves are strongly elongated and look like long hair-like formations ending with a meristem. From this meristem develops an embryo with a rudimentary stem, roots and leaves; if the tip of the leaf of the parent plant leans down and touches the ground or moss, the primordium begins to grow. The new plant is separated from the parent after the depletion of this hairy formation. The leaves of the succulent houseplant Kalanchoe bear well-developed plants along the edges, which easily fall off. New shoots and roots form on the surface of begonia leaves. Special little bodies, called germinal 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.

General information

Regeneration(from lat. regeneratio- revival) - restoration (reimbursement) of the structural elements of the tissue in exchange for the dead. In a biological sense, regeneration is adaptive process, developed in the course of evolution and inherent in all living things. In the life of an organism, each functional function requires the expenditure of a material substrate and its restoration. Therefore, during regeneration, self-reproduction of living matter, moreover, this self-reproduction of the living reflects principle of autoregulation and automation of vital functions(Davydovsky I.V., 1969).

The regenerative restoration of the structure can occur at different levels - molecular, subcellular, cellular, tissue and organ, however, it is always about the replacement of a structure that is capable of performing a specialized function. Regeneration is restoration of both structure and function. The value of the regenerative process is in the material support of homeostasis.

Restoration of structure and function can be carried out using cellular or intracellular hyperplastic processes. On this basis, cellular and intracellular forms of regeneration are distinguished (Sarkisov D.S., 1977). For cellular form regeneration is characterized by cell reproduction in the mitotic and amitotic way, for intracellular form, which can be organoid and intraorganoid, - an increase in the number (hyperplasia) and size (hypertrophy) of ultrastructures (nucleus, nucleoli, mitochondria, ribosomes, lamellar complex, etc.) and their components (see Fig. 5, 11, 15) . intracellular form regeneration is universal, since it is characteristic of all organs and tissues. However, the structural and functional specialization of organs and tissues in phylo- and ontogeny "selected" for some the predominantly cellular form, for others - predominantly or exclusively intracellular, for the third - equally both forms of regeneration (Table 5). The predominance of one or another form of regeneration in certain organs and tissues is determined by their functional purpose, structural and functional specialization. The need to preserve the integrity of the integument of the body explains, for example, the predominance of the cellular form of regeneration of the epithelium of both the skin and mucous membranes. Specialized function of the pyramidal cell of the brain

of the brain, as well as the muscle cells of the heart, excludes the possibility of division of these cells and makes it possible to understand the need for selection in the phylo- and ontogenesis of intracellular regeneration as single form restoration of this substrate.

Table 5 Forms of regeneration in organs and tissues of mammals (according to Sarkisov D.S., 1988)

These data refute the ideas that existed until recently about the loss of the ability to regenerate by some organs and tissues of mammals, about the “bad” and “good” regenerating human tissues, that there is an “inverse relationship law” between the degree of tissue differentiation and their ability to regenerate. . It has now been established that in the course of evolution the ability to regenerate in some tissues and organs did not disappear, but took on forms (cellular or intracellular) corresponding to their structural and functional originality (Sarkisov D.S., 1977). Thus, all tissues and organs have the ability to regenerate, only its forms are different depending on the structural and functional specialization of the tissue or organ.

Morphogenesis regenerative process consists of two phases - proliferation and differentiation. These phases are especially well expressed in the cellular form of regeneration. AT proliferation phase young, undifferentiated cells multiply. These cells are called cambial(from lat. cambium- exchange, change) stem cells and progenitor cells.

Each tissue is characterized by its own cambial cells, which differ in the degree of proliferative activity and specialization, however, one stem cell may be the ancestor of several species

cells (for example, a stem cell of the hematopoietic system, lymphoid tissue, some cellular representatives of the connective tissue).

AT differentiation phase young cells mature, their structural and functional specialization occurs. The same change of hyperplasia of ultrastructures by their differentiation (maturation) underlies the mechanism of intracellular regeneration.

Regulation of the regenerative process. Among regulatory mechanisms regeneration distinguish humoral, immunological, nervous, functional.

Humoral mechanisms are implemented both in the cells of damaged organs and tissues (interstitial and intracellular regulators) and beyond (hormones, poetins, mediators, growth factors, etc.). The humoral regulators are keylons (from Greek. chalainino- weaken) - substances that can suppress cell division and DNA synthesis; they are tissue specific. Immunological mechanisms regulation is associated with "regenerative information" carried by lymphocytes. In this regard, it should be noted that the mechanisms of immunological homeostasis also determine structural homeostasis. Nervous mechanisms regenerative processes are associated primarily with the trophic function nervous system, a functional mechanisms- with a functional "request" of an organ, tissue, which is considered as a stimulus for regeneration.

The development of the regenerative process largely depends on a number of general and local conditions or factors. To general should include age, constitution, nutritional status, metabolic and hematopoietic status, local - the state of innervation, blood and lymph circulation of the tissue, the proliferative activity of its cells, the nature of the pathological process.

Classification. There are three types of regeneration: physiological, reparative and pathological.

Physiological regeneration occurs throughout life and is characterized by constant renewal of cells, fibrous structures, the main substance of connective tissue. There are no structures that would not undergo physiological regeneration. Where the cellular form of regeneration dominates, cell renewal takes place. So there is a constant change of the integumentary epithelium of the skin and mucous membranes, the secretory epithelium of the exocrine glands, the cells lining the serous and synovial membranes, the cellular elements of the connective tissue, erythrocytes, leukocytes and blood platelets, etc. In tissues and organs where the cellular form of regeneration is lost, for example, in the heart, brain, intracellular structures are renewed. Along with the renewal of cells and subcellular structures, biochemical regeneration, those. renewal of the molecular composition of all body components.

Reparative or restorative regeneration observed in various pathological processes leading to damage to cells and tissues

her. The mechanisms of reparative and physiological regeneration are the same, reparative regeneration is enhanced physiological regeneration. However, due to the fact that reparative regeneration is induced by pathological processes, it has qualitative morphological differences from the physiological one. Reparative regeneration can be complete or incomplete.

complete regeneration, or restitution, characterized by the compensation of the defect with tissue that is identical to the deceased. It develops predominantly in tissues where cellular regeneration predominates. Thus, in the connective tissue, bones, skin, and mucous membranes, even relatively large defects in an organ can be replaced by a tissue identical to the deceased by cell division. At incomplete regeneration, or substitutions, the defect is replaced by connective tissue, a scar. Substitution is characteristic of organs and tissues in which the intracellular form of regeneration predominates, or it is combined with cellular regeneration. Since during regeneration there is a restoration of a structure capable of performing a specialized function, the meaning of incomplete regeneration is not in replacing the defect with a scar, but in compensatory hyperplasia elements of the remaining specialized tissue, the mass of which increases, i.e. going on hypertrophy fabrics.

At incomplete regeneration, those. tissue healing by a scar, hypertrophy occurs as an expression of the regenerative process, therefore it is called regeneration, it contains the biological meaning of reparative regeneration. Regenerative hypertrophy can be carried out in two ways - with the help of cell hyperplasia or hyperplasia and hypertrophy of cellular ultrastructures, i.e. cell hypertrophy.

Restoration of the initial mass of the organ and its function due mainly to cell hyperplasia occurs with regenerative hypertrophy of the liver, kidneys, pancreas, adrenal glands, lungs, spleen, etc. Regenerative hypertrophy due to hyperplasia of cellular ultrastructures characteristic of the myocardium, brain, i.e. those organs where the intracellular form of regeneration predominates. In the myocardium, for example, along the periphery of the scar that replaced the infarction, the size of the muscle fibers increases significantly; they hypertrophy due to hyperplasia of their subcellular elements (Fig. 81). Both ways of regenerative hypertrophy do not exclude each other, but, on the contrary, often are combined. So, with regenerative hypertrophy of the liver, not only an increase in the number of cells in the part of the organ preserved after damage occurs, but also their hypertrophy, due to hyperplasia of ultrastructures. It cannot be ruled out that regenerative hypertrophy in the heart muscle can proceed not only in the form of fiber hypertrophy, but also by increasing the number of their constituent muscle cells.

The recovery period is usually not limited only to the fact that reparative regeneration unfolds in the damaged organ. If a

Rice. 81. Regeneration myocardial hypertrophy. Hypertrophied muscle fibers are located along the periphery of the scar

the effect of the pathogenic factor stops before the death of the cell, there is a gradual restoration of damaged organelles. Consequently, the manifestations of the reparative reaction should be expanded by including restorative intracellular processes in dystrophically altered organs. The generally accepted opinion about regeneration only as the final stage of the pathological process is hardly justified. Reparative regeneration is not local, a general reaction organism, covering various bodies, but implemented in fully only in one or the other of them.

O pathological regeneration they say in those cases when, as a result of various reasons, there is perversion of the regenerative process, violation of phase change proliferation

and differentiation. Pathological regeneration is manifested in excessive or insufficient formation of regenerating tissue (hyper- or hyporegeneration), as well as in the transformation during regeneration of one type of tissue into another [metaplasia - see. Processes of adaptation (adaptation) and compensation]. Examples are hyperproduction of connective tissue with the formation keloid, over-regeneration peripheral nerves and excessive callus formation during fracture healing, sluggish wound healing, and epithelial metaplasia at the site of chronic inflammation. Pathological regeneration usually develops with violations of general and local regeneration conditions(violation of innervation, protein and vitamin starvation, chronic inflammation etc.).

Regeneration of individual tissues and organs

Reparative regeneration of blood differs from physiological regeneration primarily in its greater intensity. In this case, active red bone marrow appears in long tubular bones in place of adipose marrow (myeloid transformation of adipose marrow). Fat cells are replaced by growing islands of hematopoietic tissue, which fills the medullary canal and looks juicy, dark red. In addition, hematopoiesis begins to occur outside the bone marrow - extramedullary, or extramedullary, hematopoiesis. Ocha-

gi extramedullary (heterotopic) hematopoiesis as a result of eviction from the bone marrow of stem cells appear in many organs and tissues - the spleen, liver, lymph nodes, mucous membranes, fatty tissue, etc.

Blood regeneration can be sharply oppressed (eg, radiation sickness, aplastic anemia, aleukia, agranulocytosis) or perverted (eg, pernicious anemia, polycythemia, leukemia). At the same time, immature, functionally defective and rapidly collapsing formed elements enter the blood. In such cases, one speaks of pathological regeneration of blood.

The reparative capabilities of the organs of the hematopoietic and immunocompetent systems are ambiguous. Bone marrow has very high plastic properties and can be restored even with significant damage. The lymph nodes they regenerate well only in those cases when the connections of the afferent and efferent lymphatic vessels with the surrounding connective tissue are preserved. Tissue regeneration spleen when damaged, it is usually incomplete, the dead tissue is replaced by a scar.

Regeneration of blood and lymph vessels proceeds ambiguously depending on their caliber.

microvessels have a greater ability to regenerate than large vessels. New formation of microvessels can occur by budding or autogenously. During vascular regeneration by budding (Fig. 82) lateral protrusions appear in their wall due to intensively dividing endothelial cells (angioblasts). Strands are formed from the endothelium, in which gaps appear and blood or lymph from the "mother" vessel enters them. Other elements: the vascular wall is formed due to the differentiation of the endothelium and connective tissue cells surrounding the vessel. Nerve fibers from preexisting nerves grow into the vascular wall. Autogenic neoplasm vessels consists in the fact that foci of undifferentiated cells appear in the connective tissue. In these foci, gaps appear, into which pre-existing capillaries open and blood flows out. Young connective tissue cells differentiate and form the endothelial lining and other elements of the vessel wall.

Rice. 82. Vessel regeneration by budding

Large vessels do not have sufficient plastic properties. Therefore, if their walls are damaged, only the structures of the inner shell, its endothelial lining, are restored; elements of the middle and outer shells are usually replaced by connective tissue, which often leads to narrowing or obliteration of the vessel lumen.

Connective tissue regeneration begins with the proliferation of young mesenchymal elements and neoplasms of microvessels. A young connective tissue rich in cells and thin-walled vessels is formed, which has characteristic appearance. This is a juicy dark red fabric with a granular surface, as if strewn with large granules, which was the basis for calling it granulation tissue. Granules are loops of newly formed thin-walled vessels protruding above the surface, which form the basis of granulation tissue. Between the vessels there are many undifferentiated lymphocyte-like connective tissue cells, leukocytes, plasma cells and mastocytes (Fig. 83). Later on, it happens maturation granulation tissue, which is based on the differentiation of cellular elements, fibrous structures, and also vessels. The number of hematogenous elements decreases, and fibroblasts - increases. In connection with the synthesis of collagen fibroblasts in the intercellular spaces are formed argyrophilic(see Fig. 83), and then collagen fibers. The synthesis of glycosaminoglycans by fibroblasts serves to form

basic substance connective tissue. As fibroblasts mature, the number of collagen fibers increases, they are grouped into bundles; at the same time, the number of vessels decreases, they differentiate into arteries and veins. The maturation of granulation tissue ends with the formation coarse fibrous scar tissue.

New formation of connective tissue occurs not only when it is damaged, but also when other tissues are incompletely regenerated, as well as during organization (encapsulation), wound healing, and productive inflammation.

The maturation of granulation tissue may have certain deviations. Inflammation that develops in the granulation tissue leads to a delay in its maturation,

Rice. 83. granulation tissue. There are many undifferentiated connective tissue cells and argyrophilic fibers between the thin-walled vessels. Silver impregnation

and excessive synthetic activity of fibroblasts - to excessive formation of collagen fibers with their subsequent pronounced hyalinosis. In such cases, scar tissue appears in the form of a tumor-like formation of a bluish-red color, which rises above the surface of the skin in the form keloid. Keloid scars are formed after various traumatic skin lesions, especially after burns.

Regeneration of adipose tissue occurs due to the neoplasm of connective tissue cells, which turn into fat (adiposocytes) by accumulating lipids in the cytoplasm. Fat cells are folded into lobules, between which there are connective tissue layers with vessels and nerves. Regeneration of adipose tissue can also occur from the nucleated remnants of the cytoplasm of fat cells.

Regeneration bone tissue in case of bone fracture, it largely depends on the degree of bone destruction, the correct reposition of bone fragments, local conditions (circulatory status, inflammation, etc.). At uncomplicated bone fracture, when bone fragments are motionless, may occur primary bone union(Fig. 84). It begins with growing into the area of ​​the defect and hematoma between bone fragments of young mesenchymal elements and vessels. There is a so-called preliminary connective tissue callus, in which bone formation begins immediately. It is associated with the activation and proliferation osteoblasts in the area of ​​damage, but primarily in the periostat and endostat. In the osteogenic fibroreticular tissue, low-calcified bone trabeculae appear, the number of which increases.

Formed preliminary callus. In the future, it matures and turns into a mature lamellar bone - this is how

Rice. 84. Primary bone fusion. Intermediary callus (shown by an arrow), soldering bone fragments (according to G.I. Lavrishcheva)

definitive callus, which in its structure differs from bone tissue only in the disorderly arrangement of the bone crossbars. After the bone begins to perform its function and a static load appears, the newly formed tissue undergoes restructuring with the help of osteoclasts and osteoblasts, bone marrow appears, vascularization and innervation are restored. In case of violation of local conditions of bone regeneration (circulatory disorder), mobility of fragments, extensive diaphyseal fractures, secondary bone union(Fig. 85). This type of bone fusion is characterized by the formation between bone fragments, first of cartilage tissue, on the basis of which bone tissue is built. Therefore, with secondary bone fusion they speak of preliminary osteochondral callus, which develops into mature bone over time. Secondary bone fusion compared with the primary is much more common and takes longer.

At adverse conditions bone regeneration may be impaired. Thus, when a wound becomes infected, bone regeneration is delayed. Bone fragments, which in the normal course of the regenerative process act as a framework for the newly formed bone tissue, support inflammation under conditions of wound suppuration, which inhibits regeneration. Sometimes primary bone-cartilaginous callus is not differentiated into bone callus. In these cases, the ends of the broken bone remain movable, forming false joint. Excess production of bone tissue during regeneration leads to the appearance of bone outgrowths - exostoses.

Cartilage regeneration in contrast to the bone occurs usually incomplete. Only small defects can be replaced by newly formed tissue due to the cambial elements of the perichondrium - chondroblasts. These cells create the basic substance of cartilage, then turn into mature cartilage cells. Large cartilage defects are replaced by scar tissue.

regeneration of muscle tissue, its possibilities and forms are different depending on the type of this fabric. Smooth mice, whose cells are capable of mitosis and amitosis, with minor defects can regenerate quite completely. Significant areas of damage to smooth muscles are replaced by a scar, while the remaining muscle fibers undergo hypertrophy. New formation of smooth muscle fibers can occur by transformation (metaplasia) of connective tissue elements. This is how bundles of smooth muscle fibers are formed in pleural adhesions, in thrombi undergoing organization, in vessels during their differentiation.

striated muscles regenerate only when the sarcolemma is preserved. Inside the tubes from the sarcolemma, its organelles are regenerated, resulting in the appearance of cells called myoblasts. They stretch, the number of nuclei in them increases, in the sarcoplasm

Rice. 85. Secondary bone fusion (according to G.I. Lavrishcheva):

a - osteocartilaginous periosteal callus; a piece of bone tissue among the cartilage (microscopic picture); b - periosteal bone and cartilage callus (histotopogram 2 months after surgery): 1 - bone part; 2 - cartilaginous part; 3 - bone fragments; c - periosteal callus soldering displaced bone fragments

myofibrils differentiate, and the sarcolemma tubes turn into striated muscle fibers. Skeletal muscle regeneration may also be associated with satellite cells, which are located under the sarcolemma, i.e. inside the muscle fiber, and are cambial. In the event of an injury, satellite cells begin to divide intensively, then undergo differentiation and ensure the restoration of muscle fibers. If, when the muscle is damaged, the integrity of the fibers is violated, then at the ends of their ruptures, flask-shaped bulges appear, which contain a large number of nuclei and are called muscle kidneys. In this case, the restoration of the continuity of the fibers does not occur. The rupture site is filled with granulation tissue, which turns into a scar (muscle callus). Regeneration heart muscles when it is damaged, as with damage to the striated muscles, it ends with scarring of the defect. However, in the remaining muscle fibers, intense hyperplasia of ultrastructures occurs, which leads to fiber hypertrophy and restoration of organ function (see Fig. 81).

Epithelial regeneration in most cases, it is carried out quite completely, since it has a high regenerative capacity. Regenerates especially well cover epithelium. Recovery keratinized stratified squamous epithelium possible even with fairly large skin defects. During the regeneration of the epidermis at the edges of the defect, there is an increased reproduction of cells of the germinal (cambial), germ (Malpighian) layer. The resulting epithelial cells first cover the defect in one layer. In the future, the layer of the epithelium becomes multilayer, its cells differentiate, and it acquires all the signs of the epidermis, which includes growth, granular shiny (on the soles and palmar surface brushes) and the stratum corneum. In violation of the regeneration of the skin epithelium, non-healing ulcers are formed, often with the growth of atypical epithelium in their edges, which can serve as the basis for the development of skin cancer.

Integumentary epithelium of mucous membranes (stratified squamous non-keratinizing, transitional, single-layer prismatic and multinuclear ciliated) regenerates in the same way as multi-layered squamous keratinizing. The defect of the mucous membrane is restored due to the proliferation of cells lining the crypts and excretory ducts of the glands. Undifferentiated flattened epithelial cells first cover the defect with a thin layer (Fig. 86), then the cells take on a shape characteristic of the cellular structures of the corresponding epithelial lining. In parallel, the glands of the mucous membrane are partially or completely restored (for example, tubular glands of the intestine, endometrial glands).

Mesothelial regeneration the peritoneum, pleura and pericardial sac is carried out by dividing the remaining cells. Comparatively large cubic cells appear on the surface of the defect, which then flatten. With small defects, the mesothelial lining is restored quickly and completely.

The state of the underlying connective tissue is important for the restoration of the integumentary epithelium and mesothelium, since the epithelialization of any defect is possible only after it has been filled with granulation tissue.

Regeneration of specialized organ epithelium(liver, pancreas, kidneys, endocrine glands, pulmonary alveoli) is carried out according to the type regenerative hypertrophy: in areas of damage, the tissue is replaced by a scar, and along its periphery, hyperplasia and hypertrophy of parenchyma cells occur. AT liver the site of necrosis is always subject to scarring, however, in the rest of the organ, intensive neoplasm of cells occurs, as well as hyperplasia of intracellular structures, which is accompanied by their hypertrophy. As a result, the initial mass and function of the organ are quickly restored. The regenerative possibilities of the liver are almost limitless. In the pancreas, regenerative processes are well expressed both in the exocrine sections and in pancreatic islets, and the epithelium of the exocrine glands becomes the source of restoration of the islets. AT kidneys with necrosis of the epithelium of the tubules, the surviving nephrocytes reproduce and restore the tubules, but only with the preservation of the tubular basement membrane. When it is destroyed (tubulorhexis), the epithelium is not restored and the tubule is replaced by connective tissue. The dead tubular epithelium is not restored even in the case when the vascular glomerulus dies along with the tubule. At the same time, scar connective tissue grows in place of the dead nephron, and the surrounding nephrons undergo regenerative hypertrophy. in the glands internal secretion recovery processes are also represented by incomplete regeneration. AT lung after the removal of individual lobes, hypertrophy and hyperplasia of tissue elements occur in the remaining part. Regeneration of the specialized epithelium of organs can proceed atypically, which leads to the growth of connective tissue, structural reorganization and deformation of organs; in such cases one speaks of cirrhosis (liver cirrhosis, nephrocyrrhosis, pneumocirrhosis).

Regeneration of different parts of the nervous system happens ambiguously. AT head and spinal cord neoplasms of ganglion cells do not

Rice. 86. Regeneration of the epithelium in the bottom chronic ulcer stomach

even when they are destroyed, the restoration of function is possible only due to the intracellular regeneration of the remaining cells. Neuroglia, especially microglia, are characterized by a cellular form of regeneration, therefore, defects in the tissue of the head and spinal cord are usually filled with proliferating neuroglia cells - so-called glial (glial) scarring. When damaged vegetative nodes along with hyperplasia of cell ultrastructures, their neoplasm also occurs. In case of violation of integrity peripheral nerve regeneration occurs due to the central segment, which has retained its connection with the cell, while the peripheral segment dies. The multiplying cells of the Schwann sheath of the dead peripheral segment of the nerve are located along it and form a case - the so-called Büngner cord, into which regenerating axial cylinders from the proximal segment grow. The regeneration of nerve fibers ends with their myelination and restoration of nerve endings. Regenerative hyperplasia receptors pericellular synaptic devices and effectors is sometimes accompanied by hypertrophy of their terminal apparatuses. If the regeneration of the nerve is disturbed for one reason or another (a significant divergence of parts of the nerve, the development of an inflammatory process), then a scar is formed at the site of its break, in which the regenerated axial cylinders of the proximal segment of the nerve are randomly located. Similar growths occur at the ends of the cut nerves in the stump of the limb after its amputation. Such growths formed by nerve fibers and fibrous tissue are called amputation neuromas.

Wound healing

Wound healing proceeds according to the laws of reparative regeneration. The rate of wound healing, its outcomes depend on the degree and depth of wound damage, the structural features of the organ, general condition organism, applied methods of treatment. According to I.V. Davydovsky, the following types of wound healing are distinguished: 1) direct closure of an epithelial cover defect; 2) healing under the scab; 3) wound healing by primary intention; 4) wound healing by secondary intention, or wound healing through suppuration.

Direct closure of an epithelial defect- this is the simplest healing, which consists in the creeping of the epithelium on the superficial defect and closing it with an epithelial layer. Observed on the cornea, mucous membranes healing under the scab concerns small defects, on the surface of which a drying crust (scab) quickly appears from coagulated blood and lymph; the epidermis is restored under the crust, which disappears 3-5 days after the injury.

Healing by primary intention (per rimamm intentionem) observed in wounds with damage not only to the skin, but also to the underlying tissue,

and the edges of the wound are even. The wound is filled with clots of spilled blood, which protects the edges of the wound from dehydration and infection. Under the influence of proteolytic enzymes of neutrophils, a partial lysis of blood coagulation, tissue detritus occurs. Neutrophils die, they are replaced by macrophages that phagocytize red blood cells, the remnants of damaged tissue; hemosiderin is found in the edges of the wound. Part of the contents of the wound is removed on the first day of injury along with exudate on its own or when treating the wound - primary cleansing. On the 2-3rd day, fibroblasts and newly formed capillaries growing towards each other appear at the edges of the wound, granulation tissue, the layer of which at primary tension does not reach large sizes. By the 10-15th day, it fully matures, the wound defect epithelizes and the wound heals with a delicate scar. In a surgical wound, healing by primary intention is accelerated due to the fact that its edges are pulled together with threads of silk or catgut, around which giant cells that absorb them accumulate foreign bodies that do not interfere with healing.

Healing by secondary intention (per secundam intentionem), or healing through suppuration (or healing by granulation - per granulationem), It is usually observed with extensive wounds, accompanied by crushing and necrosis of tissues, penetration of foreign bodies and microbes into the wound. At the site of the wound, hemorrhages occur, traumatic edema of the edges of the wound, signs of demarcation quickly appear. purulent inflammation on the border with dead tissue, melting of necrotic masses. During the first 5-6 days, rejection of necrotic masses occurs - secondary cleansing of the wound, and granulation tissue begins to develop at the edges of the wound. granulation tissue, performing the wound, consists of 6 layers passing into each other (Anichkov N.N., 1951): superficial leukocyte-necrotic layer; superficial layer of vascular loops, layer of vertical vessels, maturing layer, layer of horizontally located fibroblasts, fibrous layer. The maturation of granulation tissue during wound healing by secondary intention is accompanied by regeneration of the epithelium. However, with this type of wound healing, a scar is always formed in its place.