Excitable tissues professor N. E. Vvedensky, studying the work of a neuromuscular drug when exposed to various stimuli.
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Causes of parabiosis
These are a variety of damaging effects on excitable tissue or cells that do not lead to gross structural changes, but to one degree or another disrupt it functional state. Such reasons may be mechanical, thermal, chemical and other irritants.
The essence of the phenomenon of parabiosis
As Vvedensky himself believed, the basis of parabiosis is a decrease in excitability and conductivity associated with sodium inactivation. Soviet cytophysiologist N.A. Petroshin believed that parabiosis was based on reversible changes in protoplasmic proteins. Under the influence of a damaging agent, a cell (tissue), without losing its structural integrity, completely stops functioning. This condition develops in phases, as the damaging factor acts (that is, it depends on the duration and strength of the acting stimulus). If the damaging agent is not removed in time, then biological death cells (tissues). If this agent is removed in time, the tissue also returns to its normal state in phases.
Experiments by N.E. Vvedensky
Vvedensky conducted experiments on a frog neuromuscular preparation. On sciatic nerve Test stimuli of different strengths were sequentially applied to the neuromuscular preparation. One stimulus was weak (threshold strength), that is, it caused a minimal contraction calf muscle. The other stimulus was strong (maximal), that is, the smallest of those that cause maximum contraction of the gastrocnemius muscle. Then, at some point, a damaging agent was applied to the nerve and every few minutes the neuromuscular preparation was tested: alternately with weak and strong stimuli. At the same time, the following stages developed successively:
- Equalization when in response to a weak stimulus the magnitude of muscle contraction did not change, but in response to a strong stimulus the amplitude of muscle contraction sharply decreased and became the same as in response to a weak stimulus;
- Paradoxical when, in response to a weak stimulus, the magnitude of the muscle contraction remained the same, and in response to a strong stimulus, the magnitude of the contraction amplitude became smaller than in response to a weak stimulus, or the muscle did not contract at all;
- Brake, when the muscle did not respond to both strong and weak stimuli by contracting. It is this state of tissue that is referred to as parabiosis.
Biological significance of parabiosis
. For the first time, a similar effect was noticed in cocaine, however, due to toxicity and addictive properties, this moment safer analogues are used - lidocaine and tetracaine. One of Vvedensky’s followers, N.P. Rezvyakov proposed to consider pathological process as a stage of parabiosis, therefore, for its treatment it is necessary to use antiparabiotic agents.Causes of parabiosis
These are a variety of damaging effects on excitable tissue or cells that do not lead to gross structural changes, but to one degree or another disrupt its functional state. Such reasons may be mechanical, thermal, chemical and other irritants.
The essence of the phenomenon of parabiosis
As Vvedensky himself believed, the basis of parabiosis is a decrease in excitability and conductivity associated with sodium inactivation. Soviet cytophysiologist N.A. Petroshin believed that parabiosis was based on reversible changes in protoplasmic proteins. Under the influence of a damaging agent, a cell (tissue), without losing its structural integrity, completely stops functioning. This condition develops in phases, as the damaging factor acts (that is, it depends on the duration and strength of the acting stimulus). If the damaging agent is not removed in time, biological death of the cell (tissue) occurs. If this agent is removed in time, the tissue also returns to its normal state in phases.
Experiments by N.E. Vvedensky
Vvedensky conducted experiments on a frog neuromuscular preparation. Test stimuli of varying strengths were sequentially applied to the sciatic nerve of the neuromuscular preparation. One stimulus was weak (threshold strength), that is, it caused a minimal contraction of the calf muscle. The other stimulus was strong (maximal), that is, the smallest of those that cause maximum contraction of the gastrocnemius muscle. Then, at some point, a damaging agent was applied to the nerve and every few minutes the neuromuscular preparation was tested: alternately with weak and strong stimuli. At the same time, the following stages developed successively:
- Equalization when in response to a weak stimulus the magnitude of muscle contraction did not change, but in response to a strong stimulus the amplitude of muscle contraction sharply decreased and became the same as in response to a weak stimulus;
- Paradoxical when, in response to a weak stimulus, the magnitude of the muscle contraction remained the same, and in response to a strong stimulus, the magnitude of the contraction amplitude became smaller than in response to a weak stimulus, or the muscle did not contract at all;
- Brake, when the muscle did not respond to both strong and weak stimuli by contracting. It is this state of tissue that is referred to as parabiosis.
Biological significance of parabiosis
Parabiosis is not only a laboratory phenomenon, but a phenomenon that, under certain conditions, can develop in a whole organism. For example, a parabiotic phenomenon develops in the brain during sleep. It should be noted that parabiosis as a physiological phenomenon is subject to the general biological law of force, with the difference that as the stimulus increases, the tissue response does not increase, but decreases.
Medical significance of parabiosis
Parabiosis underlies the action of local anesthetics. They reversibly bind to specific sites located inside voltage-gated sodium channels. For the first time, a similar effect was noticed in cocaine, however, due to toxicity and the ability to cause addiction, safer analogs are currently used - lidocaine and tetracaine. One of Vvedensky’s followers, N.P. Rezvyakov proposed to consider the pathological process as a stage of parabiosis, therefore, for its treatment it is necessary to use antiparabiotic agents.
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Synonyms:See what “Parabiosis” is in other dictionaries:
Parabiosis… Spelling dictionary-reference book
parabiosis- functional changes in the nerve after exposure to strong and prolonged stimuli, described by N. E. Vvedensky. If normal conditions are characterized by a direct and relatively proportional relationship of force applied to the nerve... ... Great psychological encyclopedia
Splicing, crossing Dictionary of Russian synonyms. parabiosis noun, number of synonyms: 2 crossing (27) ... Synonym dictionary
PARABIOSIS- (from the Greek para near and bios life), a term with a double meaning. 1. The connection of two organisms in order to study mutual influences through the circulatory and lymphatic systems. Parabiosis experiments were carried out on mammals, birds and... ... Big medical encyclopedia
- (from steam... and Greek bios life) 1) the reaction of living tissue to the influence of stimuli (with a certain strength and duration of their action), accompanied by reversible changes in its basic properties of excitability and conductivity. Concept and theory... ... Big encyclopedic Dictionary
- (from the Greek para near, near and bios life) functional changes in the nerve after the action of strong and prolonged stimuli on it, described by N.E. Vvedensky. If in normal conditions characteristically direct and relative... Psychological Dictionary
- (from steam... and...biosis), 1) the reaction of excitable tissue to the influence of stimuli, characterized by the fact that the altered section of the nerve (muscle) acquires low lability and therefore is not capable of carrying out a given rhythm of stimulation. Concept and... Biological encyclopedic dictionary
parabiosis- Method of producing parabiotic twins by joining circulatory systems(anastomoses) or fusion of their tissues. [Arefyev V.A., Lisovenko L.A. English Russian Dictionary genetic terms 1995 407 pp.] Topics genetics EN parabiosis ... Technical Translator's Guide
PARABIOSIS- English parabiosis German Parabiose French parabiose see > … Phytopathological dictionary-reference book
- (see para... + ... bios) 1) a method of artificial fusion of two animals, in which general blood circulation is established between them; appl. in biological experiments to study the mutual influence of organs and tissues of fused organisms... ... Dictionary foreign words Russian language
4. Lability- functional mobility, the speed of elementary cycles of excitation in the nervous and muscle tissue. The concept of "L." introduced by the Russian physiologist N. E. Vvedensky (1886), who considered the measure of L. to be the highest frequency of tissue irritation reproduced by it without converting the rhythm. L. reflects the time during which the tissue restores its performance after the next cycle of excitation. The largest L. is distinguished by its processes nerve cells- axons capable of reproducing up to 500-1000 impulses per 1 second; the central and peripheral points of contact - synapses - are less labile (for example, a motor nerve ending can transmit no more than 100-150 excitations per second to the skeletal muscle). Inhibition of the vital activity of tissues and cells (for example, by cold, drugs) reduces L., since this slows down the recovery processes and lengthens the refractory period.
Parabiosis- a state borderline between life and death of a cell.
Causes of parabiosis– a variety of damaging effects on excitable tissue or cells that do not lead to gross structural changes, but to one degree or another disrupt its functional state. Such reasons may be mechanical, thermal, chemical and other irritants.
The essence of parabiosis. As Vvedensky himself believed, the basis of parabiosis is a decrease in excitability and conductivity associated with sodium inactivation. Soviet cytophysiologist N.A. Petroshin believed that parabiosis was based on reversible changes in protoplasmic proteins. Under the influence of a damaging agent, a cell (tissue), without losing its structural integrity, completely stops functioning. This condition develops in phases, as the damaging factor acts (that is, it depends on the duration and strength of the acting stimulus). If the damaging agent is not removed in time, biological death of the cell (tissue) occurs. If this agent is removed in time, the tissue also returns to its normal state in phases.
Experiments by N.E. Vvedensky.
Vvedensky conducted experiments on a frog neuromuscular preparation. Test stimuli of varying strengths were sequentially applied to the sciatic nerve of the neuromuscular preparation. One stimulus was weak (threshold strength), that is, it caused a minimal contraction of the calf muscle. The other stimulus was strong (maximal), that is, the smallest of those that cause maximum contraction of the gastrocnemius muscle. Then, at some point, a damaging agent was applied to the nerve and every few minutes the neuromuscular preparation was tested: alternately with weak and strong stimuli. At the same time, the following stages developed successively:
1. Equalization when in response to a weak stimulus the magnitude of muscle contraction did not change, but in response to a strong stimulus the amplitude of muscle contraction sharply decreased and became the same as in response to a weak stimulus;
2. Paradoxical when, in response to a weak stimulus, the magnitude of the muscle contraction remained the same, and in response to a strong stimulus, the magnitude of the contraction amplitude became smaller than in response to a weak stimulus, or the muscle did not contract at all;
3. Brake, when the muscle did not respond to both strong and weak stimuli by contracting. It is this state of tissue that is designated as parabiosis.
PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
1. Neuron as a structural and functional unit of the central nervous system. Its physiological properties. Structure and classification of neurons.
Neurons– this is the main structural and functional unit of the nervous system, which has specific manifestations of excitability. A neuron is capable of receiving signals, processing them into nerve impulses and conducting them to nerve endings that contact another neuron or reflex organs(muscle or gland).
Types of neurons:
1. Unipolar (have one process - an axon; characteristic of invertebrate ganglia);
2. Pseudounipolar (one process dividing into two branches; typical for ganglia of higher vertebrates).
3. Bipolar (there is an axon and a dendrite, typical for peripheral and sensory nerves);
4. Multipolar (axon and several dendrites - typical for the vertebrate brain);
5. Isopolar (it is difficult to differentiate the processes of bi- and multipolar neurons);
6. Heteropolar (it is easy to differentiate the processes of bi- and multipolar neurons)
Functional classification:
1. Afferent (sensitive, sensory - perceive signals from the external or internal environment);
2. Intercalary neurons connecting each other (provide information transfer within the central nervous system: from afferent neurons to efferent ones).
3. Efferent (motor, motor neurons - transmit the first impulses from the neuron to the executive organs).
home structural feature neuron – the presence of processes (dendrites and axons).
1 – dendrites;
2 – cell body;
3 – axon hillock;
4 – axon;
5 – Schwann cell;
6 – Ranvier interception;
7 – efferent nerve endings.
The sequential synoptic combination of all 3 neurons forms reflex arc.
Excitation, which arises in the form of a nerve impulse on any part of the membrane of a neuron, runs across its entire membrane and along all its processes: both along the axon and along the dendrites. Transmitted excitation from one nerve cell to another only in one direction- from axon transmitting neuron per perceiver neuron via synapses located on its dendrites, body or axon.
Synapses provide one-way transmission of excitation. A nerve fiber (neuron extension) can transmit nerve impulses in both directions, and one-way transmission of excitation appears only in nerve circuits, consisting of several neurons connected by synapses. It is synapses that provide one-way transmission of excitation.
Nerve cells perceive and process information coming to them. This information comes to them in the form of control chemicals: neurotransmitters . It can be in the form stimulating or brake chemical signals, as well as in the form modulating signals, i.e. those that change the state or operation of the neuron, but do not transmit excitation to it.
The nervous system plays an exceptional role integrating role in the life activity of the organism, since it unites (integrates) it into a single whole and integrates it into environment. It ensures coordinated work individual parts body ( coordination), maintaining a balanced state in the body ( homeostasis) and adaptation of the body to changes in the external or internal environment ( adaptive state and/or adaptive behavior).
A neuron is a nerve cell with processes, which is the main structural and functional unit of the nervous system. It has a structure similar to other cells: membrane, protoplasm, nucleus, mitochondria, ribosomes and other organelles.
There are three parts in a neuron: the cell body - the soma, the long process - the axon, and many short branched processes - the dendrites. The soma performs metabolic functions, the dendrites specialize in receiving signals from the external environment or from other nerve cells, the axon conducts and transmits excitation to an area remote from the dendrite zone. An axon ends in a group of terminal branches to transmit signals to other neurons or executive organs. Along with the general similarity in the structure of neurons, there is great diversity due to their functional differences (Fig. 1).
Methods for studying glands internal secretion
To study the endocrine function of organs, including the endocrine glands, the following methods are used:
Extirpation of endocrine glands.
Selective destruction or suppression of endocrine cells in the body.
Endocrine gland transplantation.
Administration of endocrine gland extracts to intact animals or after removal of the corresponding gland.
Administration of chemically pure hormones to intact animals or after removal of the corresponding gland (replacement “therapy”).
Chemical analysis of extracts and synthesis of hormonal drugs.
Methods of histological and histochemical examination of endocrine tissues
Method of parabiosis or creation of general blood circulation.
A method of introducing “labeled compounds” into the body (for example, radioactive nuclides, fluorescents).
Comparison of the physiological activity of blood flowing into and out of an organ. Allows you to detect the secretion of biologically active metabolites and hormones into the blood.
Study of hormone levels in blood and urine.
Study of the content of hormone synthesis precursors and metabolites in the blood and urine.
Study of patients with insufficient or excessive gland function.
Genetic engineering methods.
Extirpation method
Extirpation is a surgical procedure that involves removing a structural formation, such as a gland.
Extirpation (extirpatio) from Latin extirpo, extirpare - to eradicate.
A distinction is made between partial and complete extirpation.
After extirpation, the remaining body functions are studied using various methods.
Using this method, the endocrine function of the pancreas and its role in the development of diabetes mellitus, the role of the pituitary gland in the regulation of body growth, the importance of the adrenal cortex, etc.
The assumption that the pancreas has endocrine functions was confirmed in the experiments of I. Mering and O. Minkovsky (1889), who showed that its removal in dogs leads to severe hyperglycemia and glycosuria. The animals died within 2–3 weeks after surgery due to severe diabetes mellitus. It was subsequently found that these changes occur due to a lack of insulin, a hormone produced in the islet apparatus of the pancreas.
Extirpation of endocrine glands in humans is encountered in the clinic. Extirpation of the gland can be deliberate(for example, for thyroid cancer, the organ is completely removed) or random(for example, when the thyroid gland is removed, the parathyroid glands are removed).
A method of selectively destroying or suppressing endocrine cells in the body
If an organ that contains cells (tissues) performing different functions is removed, it is difficult, and sometimes not at all possible, to differentiate the physiological processes performed by these structures.
For example, when the pancreas is removed, the body loses not only the cells that produce insulin ( cells), but also cells that produce glucagon ( cells), somatostatin ( cells), gastrin (G cells), pancreatic polypeptide (PP cells). In addition, the body is deprived of an important exocrine organ that ensures digestion processes.
How to understand which cells are responsible for a particular function? In this case, you can try to selectively damage some cells and determine the missing function.
Thus, when alloxan (mesoxalic acid ureide) is administered, selective necrosis occurs cells of the islets of Langerhans, which makes it possible to study the consequences of impaired insulin production without changing other functions of the pancreas. Hydroxyquinoline derivative - dithizone interferes with metabolism cells forms a complex with zinc, which also disrupts their endocrine function.
The second example is selective damage to follicular cells thyroid gland ionizing radiation radioactive iodine (131I, 132I). When using this principle for therapeutic purposes, they talk about selective strumectomy, while surgical extirpation for the same purposes is called total, subtotal.
This type of methods also includes monitoring patients with cell damage as a result of immune aggression or autoaggression, and the use of chemical (medicine) agents that inhibit the synthesis of hormones. For example: antithyroid drugs - Mercazolil, popilthiouracil.
Endocrine gland transplant method
The gland can be transplanted into the same animal after its preliminary removal (autotransplantation) or into intact animals. In the latter case it applies homo- And heterotransplantation.
In 1849, the German physiologist Adolf Berthold established that transplanting a castrated rooster into abdominal cavity testes of another rooster leads to the restoration of the original properties of the castrato. This date is considered the birth date of endocrinology.
At the end of the 19th century, Steinach showed that transplantation of the gonads guinea pigs and rats changes their behavior and life expectancy.
In the 20s of our century, transplantation of the gonads for the purpose of “rejuvenation” was used by Brown-Séquard and was widely used by the Russian scientist S. Vorontsov in Paris. These transplantation experiments provided rich factual material about the biological effects of gonadal hormones.
In an animal with an endocrine gland removed, it can be reimplanted in a well-vascularized area of the body, such as under the kidney capsule or in the anterior chamber of the eye. This operation is called reimplantation.
Hormone administration method
Endocrine gland extract or chemically pure hormones may be administered. Hormones are administered to intact animals or after removal of the corresponding gland (replacement “therapy”).
In 1889, 72-year-old Brown Sequard reported experiments conducted on himself. Extracts from animal testes had a rejuvenating effect on the scientist’s body.
Thanks to the use of the method of introducing endocrine gland extracts, the presence of insulin and somatotropin, thyroid hormones and parathyroid hormone, corticosteroids, etc. was established.
A variation of the method is feeding animals with dry gland or preparations prepared from tissues.
Using clean hormonal drugs made it possible to establish their biological effects. Disorders that occur after surgical removal of an endocrine gland can be corrected by introducing into the body a sufficient amount of an extract of this gland or an individual hormone.
The use of these methods in intact animals led to the manifestation of feedback in the regulation of endocrine organs, because the artificial excess of the hormone created caused suppression of the secretion of the endocrine organ and even atrophy of the gland.
Chemical analysis of extracts and synthesis of hormonal drugs
Producing chemical structural analysis extracts from endocrine tissue, it was possible to establish the chemical nature and identify the hormones of the endocrine organs, which subsequently led to the artificial production of effective hormonal preparations for research and therapeutic purposes.
Parabiosis method
Do not confuse with N.E. Vvedensky’s parabiosis. In this case we are talking about a phenomenon. We will talk about a method that uses cross circulation in two organisms. Parabionts are organisms (two or more) that are connected to each other through the circulatory and lymphatic systems. Such a connection can occur in nature, for example in conjoined twins, or it can be created artificially (in an experiment).
The method allows us to evaluate the role of humoral factors in changing the functions of the intact organism of one individual when interfering with the endocrine system of another individual.
Particularly important are studies of conjoined twins who share a common circulation but are separated. nervous systems. In one of the two conjoined sisters, a case of pregnancy and childbirth was described, after which lactation occurred in both sisters, and feeding was possible from four mammary glands.
Radionuclide methods
(method of labeled substances and compounds)
Note not radioactive isotopes, but substances or compounds labeled with radionuclides. Strictly speaking, radiopharmaceuticals (RP) = carrier + label (radionuclide) are introduced.
This method makes it possible to study the processes of hormone synthesis in endocrine tissue, the deposition and distribution of hormones in the body, and the routes of their elimination.
Radionuclide methods are usually divided into in vivo and in vitro studies. In in vivo studies, a distinction is made between in vivo and in vitro measurements.
First of all, all methods can be divided into in vitro - And in vivo -research (methods, diagnostics)
In vitro studies
Not to be confused in vitro - And in vivo -research (methods) with the concept in vitro - And in vivo -measurements .
With in vivo measurements there will always be in vivo studies. Those. It is impossible to measure in the body something that was not present (substance, parameter) or was not introduced as a testing agent during the study.
If a testing substance was introduced into the body, then a biosample was taken and in vitro measurements were carried out, the study should still be designated as an in vivo study.
If the test substance was not introduced into the body, but a biological sample was taken and carried out in vitro - measurements, with or without the introduction of a test substance (a reagent, for example), the study should be designated as an in vitro study.
In radionuclide in vivo diagnostics, the capture of radiopharmaceuticals from the blood by endocrine cells is more often used and is included in the resulting hormones in proportion to the intensity of their synthesis.
An example of the use of this method is the study of the thyroid gland using radioactive iodine (131I) or sodium pertechnetate (Na99mTcO4), the adrenal cortex using a labeled precursor of steroid hormones, most often cholesterol (131I cholesterol).
For in vivo radionuclide studies, radiometry or gamma topography (scintigraphy) is performed. Radionuclide scanning as a method is outdated.
Separate assessment of the inorganic and organic phases of the intrathyroidal stage of iodine metabolism.
When studying the circuits of self-government of hormonal regulation in in vivo studies, stimulation and suppression tests are used.
Let's solve two problems.
To determine the nature of the palpable formation in the right lobe of the thyroid gland (Fig. 1), 131I scintigraphy was performed (Fig. 2).
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Fig.1 |
Fig.2 |
Fig.3 |
Some time after the hormone was administered, scintigraphy was repeated (Fig. 3). The accumulation of 131I in the right lobe did not change, but in the left it appeared. What study was performed on the patient, with what hormone? Draw a conclusion based on the results of the study.
Second task.
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Fig.1 |
Fig.2 |
Fig.3 |
To determine the nature of the palpable formation in the right lobe of the thyroid gland (Fig. 1), 131I scintigraphy was performed (Fig. 2). Some time after the hormone was administered, scintigraphy was repeated (Fig. 3). The accumulation of 131I in the right lobe did not change, in the left it disappeared. What study was performed on the patient, with what hormone? Draw a conclusion based on the results of the study.
To study the sites of binding, accumulation and metabolism of hormones, they are labeled with radioactive atoms, introduced into the body, and autoradiography is used. Sections of the tissue being studied are placed on radiosensitive photographic material, such as X-ray film, developed, and the dark spots are compared with photographs of histological sections.
Study of hormone content in biosamples
More often, blood (plasma, serum) and urine are used as bioassays.
This method is one of the most accurate for assessing the secretory activity of endocrine organs and tissues, but it does not characterize the biological activity and the degree of hormonal effects in tissues.
Various research techniques are used depending on the chemical nature of the hormones, including biochemical, chromatographic and biological testing techniques, and again radionuclide techniques.
Among radionuclide honeys there are
radioimmune (RIA)
immunoradiometric (IRMA)
radioreceptor (RRA)
In 1977, Rosalyn Yalow received the Nobel Prize for her improvements in radioimmunoassay (RIA) techniques for peptide hormones.
Radioimmunoassay, which is most widespread today due to its high sensitivity, accuracy and simplicity, is based on the use of hormones labeled with iodine (125I) or tritium (3H) isotopes and specific antibodies that bind them.
Why is it needed?
A lot of blood sugar In most patients with diabetes, insulin activity in the blood is rarely reduced, more often it is normal or even increased
The second example is hypocalcemia. Parathyrin is often elevated.
Radionuclide methods make it possible to determine fractions (free, protein-bound) of hormones.
In radioreceptor analysis, the sensitivity of which is lower and the information content is higher than radioimmune analysis, the binding of a hormone is assessed not with antibodies to it, but with specific hormonal receptors cell membranes or cytosol.
When studying the contours of self-government of hormonal regulation in in vitro studies, the determination of the complete “set” of hormones of various levels of regulation associated with the process under study (liberins and statins, tropins, effector hormones) is used. For example, for the thyroid gland, thyrotropin-releasing hormone, thyrotropin, triiodotyrosine, thyroxine.
Primary hypothyroidism:
T3, T4, TSH, TL
Secondary hypothyroidism:
T3, T4, TSH, TL
Tertiary hypothyroidism:
T3, T4, TSH, TL
Relative specificity of regulation: the introduction of iodine and dioidtyrosine inhibits the production of thyrotropin.
Comparison of the physiological activity of blood flowing into and out of an organ allows us to identify the secretion of biologically active metabolites and hormones into the blood.
Study of the content of hormone synthesis precursors and metabolites in blood and urine
Often, the hormonal effect is largely determined by the active metabolites of the hormone. In other cases, precursors and metabolites whose concentrations are proportional to hormone levels are more readily available for study. The method allows not only to evaluate the hormone-producing activity of endocrine tissue, but also to identify the characteristics of hormone metabolism.
Monitoring of patients with impaired function of endocrine organs
This can provide valuable information about the physiological effects and roles of endocrine gland hormones.
Addison T. (Addison Thomas), English physician (1793-1860). He is called the father of endocrinology. Why? In 1855, he published a monograph containing, in particular, a classic description of chronic adrenal insufficiency. Soon it was proposed to call it Addison's disease. The cause of Addison's disease is most often a primary lesion of the adrenal cortex by an autoimmune process (idiopathic Addison's disease) and tuberculosis.
Methods of histological and histochemical examination of endocrine tissues
These methods make it possible to evaluate not only the structural, but also the functional characteristics of cells, in particular, the intensity of formation, accumulation and excretion of hormones. For example, the phenomena of neurosecretion of hypothalamic neurons and the endocrine function of atrial cardiomyocytes were discovered using histochemical methods.
Genetic engineering methods
These methods of reconstructing the genetic apparatus of the cell make it possible not only to study the mechanisms of hormone synthesis, but also to actively intervene in them. The mechanisms are especially promising for practical application in cases of persistent disruption of hormone synthesis, as happens in diabetes mellitus.
An example of the experimental use of the method is a study by French scientists who, in 1983, transplanted a gene that controls insulin synthesis into the liver of a rat. The introduction of this gene into the nuclei of rat liver cells led to the fact that the liver cells synthesized insulin within a month.
NOT. Vvedensky in 1902 he showed that a section of a nerve that has undergone alteration - poisoning or damage - acquires low lability. This means that the state of excitement that arises in this area disappears more slowly than in the normal area. Therefore, at a certain stage of poisoning, when the overlying normal area is exposed to a frequent rhythm of irritation, the poisoned area is not able to reproduce this rhythm, and excitation is not transmitted through it. N.E. Vvedensky called this state of reduced lability parabiosis(from the word “para” - around and “bios” - life), to emphasize that in the area of parabiosis, normal life activity is disrupted.
Parabiosis- this is a reversible change that, when the action of the agent that caused it deepens and intensifies, turns into an irreversible disruption of life - death.
The classic experiments of N. E. Vvedensky were carried out on a neuromuscular preparation of a frog. The nerve under study was subjected to alteration in a small area, i.e., a change in its state was caused under the influence of the application of any chemical agent - cocaine, chloroform, phenol, potassium chloride, strong faradic current, mechanical damage etc. Irritation was applied either to the poisoned area of the nerve or above it, that is, in such a way that the impulses arose in the parabiotic area or passed through it on their way to the muscle. N. E. Vvedensky judged the conduction of excitation along a nerve by muscle contraction.
In a normal nerve, an increase in the strength of rhythmic stimulation of the nerve leads to an increase in the force of tetanic contraction ( rice. 160, A). With the development of parabiosis, these relationships naturally change, and the following successive stages are observed.
- Provisional, or equalizing, phase. During this initial phase of alteration, the ability of the nerve to conduct rhythmic impulses decreases with any strength of irritation. However, as Vvedensky showed, this decrease affects the effects of stronger stimuli more sharply than more moderate ones: as a result of this, the effects of both are almost equal ( rice. 160, B).
- Paradoxical phase follows the equalizing phase and is the most characteristic phase of parabiosis. According to N. E. Vvedensky, it is characterized by the fact that strong excitations emerging from normal points of the nerve are not transmitted at all to the muscle through the anesthetized area or cause only initial contractions, while very moderate excitations are capable of causing quite significant tetanic contractions ( rice. 160, V).
- Braking phase- the last stage of parabiosis. During this period, the nerve completely loses the ability to conduct excitation of any intensity.
The dependence of the effects of nerve irritation on the strength of the current is due to the fact that as the strength of the stimuli increases, the number of excited nerve fibers increases and the frequency of impulses arising in each fiber increases, since a strong stimulus can cause a volley of impulses.
Thus, the nerve reacts with a high frequency of excitations in response to strong stimulation. With the development of parabiosis, the ability to reproduce frequent rhythms, i.e. lability, decreases. This leads to the development of the phenomena described above.
With low strength or a rare rhythm of stimulation, each impulse generated in an undamaged area of the nerve is also conducted through the parabiotic area, since by the time it arrives in this area, the excitability, reduced after the previous impulse, has time to fully recover.
With strong irritation, when impulses follow each other with high frequency, each subsequent impulse arriving at the parabiotic site enters a stage of relative refractoriness after the previous one. At this stage, the excitability of the fiber is sharply reduced, and the amplitude of the response is reduced. Therefore, spreading excitation does not occur, but only an even greater decrease in excitability occurs.
In the area of parabiosis, impulses coming quickly one after another seem to block their own path. During the equalizing phase of parabiosis, all these phenomena are still weakly expressed, so only a transformation of a frequent rhythm into a rarer one occurs. As a result, the effects of frequent (strong) and relatively rare (moderate) stimulation are equalized, while at the paradoxical stage the cycles of excitability restoration are so prolonged that frequent (strong) stimulation generally turns out to be ineffective.
With particular clarity, these phenomena can be traced on single nerve fibers when irritated by stimuli. different frequencies. Thus, I. Tasaki influenced one of the interceptions of Ranvier of the myelinated nerve fiber of a frog with a solution of urethane and studied the conduction of nerve impulses through such an interception. He showed that while rare stimuli passed through the interception unimpeded, frequent ones were blocked by it.
N. E. Vvedensky considered parabiosis as a special state of persistent, unwavering excitation, as if frozen in one section of the nerve fiber. He believed that the waves of excitation coming to this area from the normal parts of the nerve, as it were, sum up with the “stationary” excitation present here and deepen it. N. E. Vvedensky considered this phenomenon as a prototype of the transition of excitation to inhibition in nerve centers. Inhibition, according to N. E. Vvedensky, is the result of “overexcitation” of a nerve fiber or nerve cell.
