Any living organism is a complex multilevel dynamic structure in which processes of substance breakdown and synthesis, death of tissue cells, and formation of new cells in place of dead ones are constantly occurring. Under physiological conditions, these processes occur continuously and are aimed at maintaining the functions of cells, tissues, and organs at a level that ensures the vital activity of the entire organism in accordance with the conditions in which it exists. These processes constitute physiological regeneration, which is the basis of all manifestations of normal vital activity.
Physiological regeneration is based on two types of restoration or renewal – intracellular and cellular. They represent the elementary form of regeneration and are universal. In cellular regeneration, continuous intracellular renewal is accompanied by replacement of the cellular composition of tissues. Each form of physiological regeneration is an evolutionarily determined process that best corresponds to the structural and functional characteristics of a particular organ. From a histogenetic perspective, physiological regeneration is the process of restoring worn-out cells or intracellular structures by intensifying certain processes that constitute histogenesis. During organism development, regenerative activity changes. In early stages it is mainly represented by mitotic division, which ensures intensive growth. Later, as organs mature and growth slows, regenerative activity becomes increasingly differentiated: in some organs mitosis and division remain the main form of regeneration, while in others they are, to varying degrees, replaced by intracellular forms of regeneration.
Depending on the characteristics of regeneration in organs and tissues, they are divided into three groups. Organs and tissues in which intracellular regeneration is the only or predominant form belong to the first group. This group includes ganglion cells of the central nervous system and myocardium. The second group includes organs such as the liver, kidneys, lungs, skeletal muscles, and others, in which continuous intracellular renewal is accompanied by renewal of cellular composition (cellular regeneration). However, under ordinary conditions of life, the cellular form of physiological regeneration in these organs is much less pronounced than the intracellular form. In organs of the third group (bones, epidermis, mucous membranes, endothelium, and others), cellular physiological regeneration predominates over intracellular regeneration.
During intracellular regeneration, restoration of organ function intensity occurs through genome reproduction in non-dividing cells and formation of polyploid cells. Cellular regeneration of organs and tissues is based on a set of stem cells, progenitor cells, and mature differentiated cells. Together they form a cellular differon and participate in regeneration according to their potential for proliferation and differentiation.
Physiological regeneration processes that occur during normal vital activity are also fundamental under the influence of extreme factors. When environmental influences go beyond physiological limits, more or less pronounced functional and morphological disorders of organs arise. These disorders manifest as dystrophic and necrotic changes in cells. In such cases, it becomes necessary not only to intensify physiological regeneration, but also to eliminate the cellular defect of tissue that has occurred. Therefore, physiological regeneration developing in response to extreme exposure is called reparative regeneration. Repair of damage in each organ occurs in the same way as physiological renewal of its structure. In organs and tissues where physiological regeneration occurs through continuous renewal of cellular composition, reparative regeneration proceeds through cell multiplication. In organs and tissues where intracellular and cellular physiological regeneration are expressed to approximately the same degree, repair occurs both by increasing the cellular composition and by hyperplasia of ultrastructures in preserved cells. Restoration of damaged organs and tissues characterized by intracellular physiological regeneration occurs only through hyperplasia of ultrastructures in preserved cells.
Regardless of which tissue group it occurs in, repair anatomically ends in one of two variants. In some cases, a necrotic tissue area formed during a pathological process is filled with tissue identical to the lost tissue. This is complete tissue repair or restitution. In cases where the necrotic area is filled with connective tissue and normalization of impaired functions is achieved through cellular hyperplasia, incomplete repair or substitution occurs.
Despite common features between physiological regeneration and repair, there are also differences related to the biological conditions of both processes. In physiological regeneration, restoration of lost structures occurs under conditions of normal tissue and organ function; in reparative processes, it occurs under conditions of loss or limitation of function. The speed of restoration processes is also significantly different. Under pathological conditions, the intensity of anabolic processes increases tens of times compared with normal. An important link in regeneration is the interaction between lymphocytes, macrophages, and progenitor cells. The main connecting link in cellular relationships during regeneration is the macrophage, which maintains direct and feedback contacts with lymphocytes and acts on the executive link – the progenitor cell, regulating its activity.
Conventionally, the reparative process can be divided into two consecutive stages. During the first stage, which develops immediately in response to excessive external influence, the balance between the rate of structural destruction and the intensity of restoration is disturbed in favor of destruction. This leads first to dystrophic and then to necrotic processes in cells. During the second stage, synthetic processes sharply increase and gradually begin to prevail over breakdown processes. This stage is the actual reparative stage. After repair is completed, the dynamic balance between breakdown and synthesis of substances is restored, and regeneration acquires a physiological character. It is important that the duration of the first stage determines when actual repair of the damaged area begins.
Thus, from general biological and general pathological perspectives, regeneration is the process of renewal of cellular (structural) elements of the organism under normal functioning conditions or restoration of their number after damage, ensuring normalization of impaired functions in pathological processes.
Any living organism is a complex multilevel dynamic structure in which processes of substance breakdown and synthesis, death of tissue cells, and formation of new cells in place of dead ones are constantly occurring. Under physiological conditions, these processes occur continuously and are aimed at maintaining the functions of cells, tissues, and organs at a level that ensures the vital activity of the entire organism in accordance with the conditions in which it exists. These processes constitute physiological regeneration, which is the basis of all manifestations of normal vital activity.
Physiological regeneration is based on two types of restoration or renewal – intracellular and cellular. They represent the elementary form of regeneration and are universal. In cellular regeneration, continuous intracellular renewal is accompanied by replacement of the cellular composition of tissues. Each form of physiological regeneration is an evolutionarily determined process that best corresponds to the structural and functional characteristics of a particular organ. From a histogenetic perspective, physiological regeneration is the process of restoring worn-out cells or intracellular structures by intensifying certain processes that constitute histogenesis. During organism development, regenerative activity changes. In early stages it is mainly represented by mitotic division, which ensures intensive growth. Later, as organs mature and growth slows, regenerative activity becomes increasingly differentiated: in some organs mitosis and division remain the main form of regeneration, while in others they are, to varying degrees, replaced by intracellular forms of regeneration.
Depending on the characteristics of regeneration in organs and tissues, they are divided into three groups. Organs and tissues in which intracellular regeneration is the only or predominant form belong to the first group. This group includes ganglion cells of the central nervous system and myocardium. The second group includes organs such as the liver, kidneys, lungs, skeletal muscles, and others, in which continuous intracellular renewal is accompanied by renewal of cellular composition (cellular regeneration). However, under ordinary conditions of life, the cellular form of physiological regeneration in these organs is much less pronounced than the intracellular form. In organs of the third group (bones, epidermis, mucous membranes, endothelium, and others), cellular physiological regeneration predominates over intracellular regeneration.
During intracellular regeneration, restoration of organ function intensity occurs through genome reproduction in non-dividing cells and formation of polyploid cells. Cellular regeneration of organs and tissues is based on a set of stem cells, progenitor cells, and mature differentiated cells. Together they form a cellular differon and participate in regeneration according to their potential for proliferation and differentiation.
Physiological regeneration processes that occur during normal vital activity are also fundamental under the influence of extreme factors. When environmental influences go beyond physiological limits, more or less pronounced functional and morphological disorders of organs arise. These disorders manifest as dystrophic and necrotic changes in cells. In such cases, it becomes necessary not only to intensify physiological regeneration, but also to eliminate the cellular defect of tissue that has occurred. Therefore, physiological regeneration developing in response to extreme exposure is called reparative regeneration. Repair of damage in each organ occurs in the same way as physiological renewal of its structure. In organs and tissues where physiological regeneration occurs through continuous renewal of cellular composition, reparative regeneration proceeds through cell multiplication. In organs and tissues where intracellular and cellular physiological regeneration are expressed to approximately the same degree, repair occurs both by increasing the cellular composition and by hyperplasia of ultrastructures in preserved cells. Restoration of damaged organs and tissues characterized by intracellular physiological regeneration occurs only through hyperplasia of ultrastructures in preserved cells.
Regardless of which tissue group it occurs in, repair anatomically ends in one of two variants. In some cases, a necrotic tissue area formed during a pathological process is filled with tissue identical to the lost tissue. This is complete tissue repair or restitution. In cases where the necrotic area is filled with connective tissue and normalization of impaired functions is achieved through cellular hyperplasia, incomplete repair or substitution occurs.
Despite common features between physiological regeneration and repair, there are also differences related to the biological conditions of both processes. In physiological regeneration, restoration of lost structures occurs under conditions of normal tissue and organ function; in reparative processes, it occurs under conditions of loss or limitation of function. The speed of restoration processes is also significantly different. Under pathological conditions, the intensity of anabolic processes increases tens of times compared with normal. An important link in regeneration is the interaction between lymphocytes, macrophages, and progenitor cells. The main connecting link in cellular relationships during regeneration is the macrophage, which maintains direct and feedback contacts with lymphocytes and acts on the executive link – the progenitor cell, regulating its activity.
Conventionally, the reparative process can be divided into two consecutive stages. During the first stage, which develops immediately in response to excessive external influence, the balance between the rate of structural destruction and the intensity of restoration is disturbed in favor of destruction. This leads first to dystrophic and then to necrotic processes in cells. During the second stage, synthetic processes sharply increase and gradually begin to prevail over breakdown processes. This stage is the actual reparative stage. After repair is completed, the dynamic balance between breakdown and synthesis of substances is restored, and regeneration acquires a physiological character. It is important that the duration of the first stage determines when actual repair of the damaged area begins.
Thus, from general biological and general pathological perspectives, regeneration is the process of renewal of cellular (structural) elements of the organism under normal functioning conditions or restoration of their number after damage, ensuring normalization of impaired functions in pathological processes.