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At what stage of parabiosis there is no response. Physiology of parabiosis

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 section of the nerve or above it, that is, in such a way that impulses arise in the parabiotic section or pass 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. In 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 they are irritated by stimuli of 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.

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 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, then 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

. For the first time, a similar effect was noticed in cocaine, however, due to toxicity and the ability to cause addiction, safer analogues 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.

Nerve fibers have lability- the ability to reproduce a certain number of excitation cycles per unit of time in accordance with the rhythm of existing stimuli. A measure of lability is the maximum number of excitation cycles that a nerve fiber can reproduce per unit time without transforming the rhythm of stimulation. Lability is determined by the duration of the peak of the action potential, i.e., the phase of absolute refractoriness. Since the duration of absolute refractoriness of the spike potential of a nerve fiber is the shortest, its lability is the highest. A nerve fiber can reproduce up to 1000 impulses per second.

Phenomenon parabiosis discovered by the Russian physiologist N.E. Vvedensky in 1901 while studying the excitability of a neuromuscular drug. The state of parabiosis can be caused by various influences - ultra-frequent, super-strong stimuli, poisons, drugs and other influences, both normally and in pathology. N. E. Vvedensky discovered that if a section of a nerve is subjected to alteration (i.e., exposure to a damaging agent), then the lability of such a section sharply decreases. Restoration of the initial state of the nerve fiber after each action potential in the damaged area occurs slowly. When this area is exposed to frequent stimuli, it is unable to reproduce the given rhythm of stimulation, and therefore the conduction of impulses is blocked. This state of reduced lability was called N. E. Vvedensky parabiosis. The state of parabiosis of excitable tissue occurs under the influence of strong stimuli and is characterized by phase disturbances in conductivity and excitability. There are 3 phases: primary, the phase of greatest activity (optimum) and the phase of reduced activity (pessimum). The third phase combines 3 successively replacing each other stages: equalizing (provisional, transformative - according to N.E. Vvedensky), paradoxical and inhibitory.

The first phase (primum) is characterized by a decrease in excitability and an increase in lability. In the second phase (optimum), excitability reaches its maximum, lability begins to decrease. In the third phase (pessimum), excitability and lability decrease in parallel and 3 stages of parabiosis develop. The first stage - equalizing according to I.P. Pavlov - is characterized by equalization of responses to strong, frequent and moderate irritations. IN equalization phase the magnitude of the response to frequent and rare stimuli is equalized. Under normal conditions of functioning of a nerve fiber, the magnitude of the response of the muscle fibers innervated by it obeys the law of force: the response to rare stimuli is less, and to frequent stimuli it is greater. Under the action of a parabiotic agent and with a rare rhythm of stimulation (for example, 25 Hz), all excitation impulses are conducted through the parabiotic area, since the excitability after the previous impulse has time to recover. With a high stimulation rhythm (100 Hz), subsequent impulses can arrive at a time when the nerve fiber is still in a state of relative refractoriness caused by the previous action potential. Therefore, some impulses are not carried out. If only every fourth excitation is carried out (i.e. 25 pulses out of 100), then the amplitude of the response becomes the same as for rare stimuli (25 Hz) - the response is equalized.

The second stage is characterized by a perverted response - strong irritations cause a smaller response than moderate ones. In this - paradoxical phase there is a further decrease in lability. At the same time, a response occurs to rare and frequent stimuli, but to frequent stimuli it is much less, since frequent stimuli further reduce lability, lengthening the phase of absolute refractoriness. Consequently, a paradox is observed - the response to rare stimuli is greater than to frequent ones.

IN braking phase lability is reduced to such an extent that both rare and frequent stimuli do not cause a response. In this case, the nerve fiber membrane is depolarized and does not enter the repolarization stage, i.e., its original state is not restored. Neither strong nor moderate irritations cause a visible reaction; inhibition develops in the tissue. Parabiosis is a reversible phenomenon. If the parabiotic substance does not act for long, then after its action ceases, the nerve exits the state of parabiosis through the same phases, but in the reverse order. However, under the influence of strong stimuli, the inhibitory stage may be followed by a complete loss of excitability and conductivity, and subsequently tissue death.

The works of N.E. Vvedensky on parabiosis played an important role in the development of neurophysiology and clinical medicine, showing the unity of the processes of excitation, inhibition and rest, and changed the prevailing law of force relations in physiology, according to which the greater the reaction, the stronger the acting stimulus.

The phenomenon of parabiosis underlies drug local anesthesia. The influence of anesthetic substances is associated with a decrease in lability and a disruption of the mechanism of excitation along nerve fibers.

Methods for studying endocrine glands

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 regulating body growth, the importance of the adrenal cortex, etc. were discovered.

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 thyroid follicular cells 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 auto-aggression, and the use of chemicals (medicines) 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 the testes of another rooster into the abdominal cavity of a castrated rooster leads to the restoration of the original properties of the castrate. This date is considered the birth date of endocrinology.

At the end of the 19th century, Steinach showed that transplanting gonads into guinea pigs and rats changed 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 a wealth of 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.

The use of pure hormonal drugs has 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

By performing a chemical structural analysis of 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 blood circulation but separate 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 biosample 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).


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.


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 of 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 assess 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.

Parabiosis- means "near life." It occurs when the nerves are affected parabiotic irritants(ammonia, acid, fat solvents, KCl, etc.), this irritant changes lability , reduces it. Moreover, it reduces it in phases, gradually.

^ Phases of parabiosis:

1. First observed equalization phase parabiosis. Typically, a stronger stimulus produces a stronger response, and a smaller stimulus produces a smaller response. Here, equally weak responses to stimuli of varying strengths are observed (Graphic demonstration).

2. Second phase - paradoxical phase parabiosis. A strong stimulus produces a weak response, a weak stimulus produces a strong response.

3. Third phase - braking phase parabiosis. There is no response to both weak and strong stimuli. This is due to changes in lability.

First and second phase - reversible , i.e. when the action of the parabiotic agent ceases, the tissue is restored to its normal state, to its original level.

The third phase is not reversible; the inhibitory phase after a short period of time turns into tissue death.

^ Mechanisms of occurrence of parabiotic phases

1. The development of parabiosis is due to the fact that, under the influence of a damaging factor, decreased lability, functional mobility . This is the basis of the answers that are called parabiosis phases .

2. In a normal state, tissue obeys the law of irritation strength. The greater the strength of the irritation, the greater the response. There is a stimulus that causes a maximum response. And this value is designated as the optimum frequency and strength of stimulation.

If this frequency or strength of the stimulus is exceeded, the response decreases. This phenomenon is a pessimum of frequency or strength of irritation.

3. The optimum value coincides with the lability value. Because lability is the maximum capacity of the tissue, the maximum response of the tissue. If lability changes, then the values at which a pessimum develops instead of an optimum shift. If you change the lability of the tissue, then the frequency that caused the optimum response will now cause the pessimum.

^ Biological significance of parabiosis

Vvedensky's discovery of parabiosis on a neuromuscular preparation in laboratory conditions had colossal implications for medicine:

1. Showed that the phenomenon of death not instantly , there is a transition period between life and death.

2. This transition is carried out phase by phase .

3. First and second phases reversible , and the third not reversible .

These discoveries led to the concepts in medicine - clinical death, biological death.

Clinical death- this is a reversible condition.

^ Biological death- irreversible condition.

As soon as the concept of “clinical death” was formed, a new science appeared - resuscitation(“re” is a reflexive preposition, “anima” is life).

^ 9. Action of direct current...

Direct current exerts on the fabric two types of action:

1. Exciting effect

2. Electrotonic action.

The exciting action is formulated in Pfluger’s three laws:

1. When a direct current acts on tissue, excitation occurs only at the moment of closing the circuit or at the moment of opening the circuit, or with a sharp change in current strength.

2. Excitation occurs when a short circuit occurs under the cathode, and when an open circuit occurs, under the anode.

3. The threshold for cathode-closing action is less than the threshold for anode-closing action.

Let's look at these laws:

1. Excitation occurs when closing and opening or when there is a strong current, because it is these processes that create the necessary conditions for the occurrence of depolarization of the membranes under the electrodes.

2. ^ Under the cathode By completing the circuit, we essentially introduce a powerful negative charge onto the outer surface of the membrane. This leads to the development of the process of depolarization of the membrane under the cathode.

^ Therefore, it is under the cathode that the excitation process occurs during closure.

Consider a cell under the anode. When the circuit is closed, a powerful positive charge is introduced onto the surface of the membrane, which leads to membrane hyperpolarization. Therefore, there is no excitation under the anode. Under the influence of current it develops accommodation. KUD shifts following the membrane potential, but to a lesser extent. Excitability decreases. No conditions for arousal

Let's open the circuit - the membrane potential will quickly return to its original level.

^ KUD cannot change quickly, it will return gradually and the rapidly changing membrane potential will reach KUD - there will be excitement . In this main reason that excitation arises at the moment of opening.

At the moment of opening under the cathode ^ The EAC slowly returns to the initial level, but the membrane potential does this quickly.

1. Under the cathode, with prolonged exposure to direct current on the tissue, a phenomenon will occur - cathodic depression.

2. An anode block will appear under the anode at the moment of short circuit.

The main symptom of cathodic depression and anode block is reduction of excitability and conductivity to zero level. However, the biological tissue remains alive.

^ Electrotonic effect of direct current on tissue.

Electrotonic action is understood as the action of direct current on tissue, which leads to a change in the physical and physiological properties of the tissue. In connection with these they distinguish two types of electroton:

Physical electroton.
Physiological electroton.

By physical electroton we mean a change in the physical properties of the membrane that occurs under the influence of direct current - a change permeability membrane, critical level of depolarization.

Physiological electroton is understood as a change in the physiological properties of tissue. Namely - excitability, conductivity under the influence of electric current.

In addition, the electroton is divided into anelectroton and catelectroton.

Anelectroton - changes in the physical and physiological properties of tissues under the influence of the anode.

Kaelectroton - changes in the physical and physiological properties of tissues under the influence of the cathode.

The permeability of the membrane will change and this will be expressed in hyperpolarization of the membrane and under the influence of the anode the AUD will gradually decrease.

In addition, under the anode, under the action of direct electric current, a physiological component of electroton. This means that under the influence of the anode the excitability changes. How does excitability change under the influence of the anode? The electric current was turned on - the CUD shifted downward, the membrane became hyperpolarized, and the level of the resting potential sharply shifted.

The difference between the KUD and the resting potential increases at the beginning of the action of electric current under the anode. Means excitability under the anode will initially decrease. The membrane potential will slowly shift down, and the CUD will move quite strongly. This will lead to the restoration of excitability to the original level, and with prolonged exposure to direct current under the anode excitability will increase, since the difference between the new level of KUD and the membrane potential will be less than at rest.

^ 10. The structure of biomembranes...

The organization of all membranes has much in common; they are built on the same principle. The basis of the membrane is a lipid bilayer (a double layer of amphiphilic lipids), which have a hydrophilic “head” and two hydrophobic “tails”. In the lipid layer, lipid molecules are spatially oriented, facing each other with hydrophobic “tails”, the heads of the molecules are facing the outer and inner surfaces of the membrane.

^ Membrane lipids: phospholipids, sphingolipids, glycolipids, cholesterol.

In addition to the formation of the bilipid layer, they perform other functions:

form an environment for membrane proteins (allosteric activators of a number of membrane enzymes);
are the predecessors of some second intermediaries;
perform an “anchor” function for some peripheral proteins.

Among membrane proteins highlight:

peripheral - located on the outer or inner surfaces of the bilipid layer; on the outer surface these include receptor proteins, adhesion proteins; on the inner surface - proteins of secondary messenger systems, enzymes;

integral - partially immersed in the lipid layer. These include receptor proteins, adhesion proteins;

transmembrane - penetrate the entire thickness of the membrane, with some proteins passing through the membrane once, while others pass repeatedly. This type of membrane proteins forms pores, ion channels and pumps, carrier proteins, and receptor proteins. Transmembrane proteins play a leading role in the interaction of the cell with the environment, ensuring signal reception, transmission into the cell, and amplification at all stages of propagation.

In the membrane, this type of protein forms domains (subunits) that ensure that transmembrane proteins perform essential functions.

The domains are based on transmembrane segments formed by nonpolar amino acid residues twisted in the form of a helix and extramembrane loops representing polar regions of proteins that can protrude quite far beyond the bilipid layer of the membrane (referred to as intracellular and extracellular segments); COOH- and NH 2 -terminal parts of the domain.

Often, the transmembrane, extra- and intracellular parts of the domain - subunits - are simply isolated. Membrane proteins also divided into:

structural proteins: give the membrane its shape, a number of mechanical properties (elasticity, etc.);
transport proteins:

form transport flows (ion channels and pumps, carrier proteins);
contribute to the creation of transmembrane potential.

proteins providing intercellular interactions:

Adhesive proteins bind cells to each other or to extracellular structures;

protein structures involved in the formation of specialized intercellular contacts (desmosomes, nexuses, etc.);
proteins directly involved in transmitting signals from one cell to another.

The membrane contains carbohydrates in the form glycolipids And glycoproteins. They form oligosaccharide chains that are located on the outer surface of the membrane.

^ Membrane properties:

1. Self-assembly in aqueous solution.

2. Closure (self-crosslinking, closure). The lipid layer always closes on itself to form completely delimited compartments. This ensures self-crosslinking when the membrane is damaged.

3. Asymmetry (transverse) - the outer and inner layers of the membrane differ in composition.

4. Fluidity (mobility) of the membrane. Lipids and proteins can, under certain conditions, move in their layer: