organism
Regulation of the functions of cells, tissues and organs, the relationship between them, i.e. the integrity of the organism, and the unity of the organism and the external environment is carried out by the nervous system and humoral way. In other words, we have two mechanisms of regulation of functions - nervous and humoral.
Nervous regulation is carried out by the nervous system, the brain and spinal cord through the nerves that are supplied to all organs of our body. The body is constantly affected by certain stimuli. The body responds to all these stimuli with a certain activity or, as it is customary to create, the body functions adapt to constantly changing environmental conditions. Thus, a decrease in air temperature is accompanied not only by a narrowing of blood vessels, but also by an increase in metabolism in cells and tissues and, consequently, an increase in heat generation. Due to this, a certain balance is established between heat transfer and heat generation, hypothermia of the body does not occur, and the constancy of body temperature is maintained. Food irritation of the taste buds of the mouth strips causes the separation of saliva and other digestive juices. under the influence of which the digestion of food occurs. Thanks to this, the necessary substances enter the cells and tissues, and a certain balance is established between dissimilation and assimilation. According to this principle, the regulation of other functions of the body occurs.
Nervous regulation is reflex in nature. Various stimuli are perceived by receptors. The resulting excitation from the receptors is transmitted through the sensory nerves to the central nervous system, and from there through the motor nerves to the organs that carry out certain activities. Such responses of the body to stimuli carried out through the central nervous system. called reflexes. The path along which excitation is transmitted during a reflex is called the reflex arc. Reflexes are varied. I.P. Pavlov divided all reflexes into unconditional and conditional. Unconditioned reflexes are congenital reflexes that are inherited. An example of such reflexes are vasomotor reflexes (constriction or expansion of blood vessels in response to skin irritation with cold or heat), salivation reflex (saliva when the taste buds are irritated by food) and many others.
Conditioned reflexes are acquired reflexes, they are developed throughout the life of an animal or person. These reflexes occur
only under certain conditions and can disappear. An example of conditioned reflexes is the separation of saliva at the sight of food, when smelling food, and in a person even when talking about it.
Humoral regulation (Humor - liquid) is carried out through the blood and other liquid and, constituting the internal environment of the body, various chemicals that are produced in the body itself or come from the external environment. Examples of such substances are hormones secreted by the endocrine glands, and vitamins that enter the body with food. Chemicals are carried by the blood throughout the body and affect various functions, in particular the metabolism in cells and tissues. Moreover, each substance affects a certain process that occurs in a particular organ.
Nervous and humoral mechanisms of regulation of functions are interconnected. Thus, the nervous system exerts a regulating influence on the organs not only directly through the nerves, but also through the endocrine glands, changing the intensity of the formation of hormones in these organs and their entry into the blood.
In turn, many hormones and other substances affect the nervous system.
In a living organism, the nervous and humoral regulation of various functions is carried out according to the principle of self-regulation, i.e. automatically. According to this principle of regulation, blood pressure, the constancy of the composition and physico-chemical properties of blood, and body temperature are maintained at a certain level. metabolism, the activity of the heart, respiratory and other organ systems during physical work, etc. change in a strictly coordinated manner.
Due to this, certain relatively constant conditions are maintained in which the activity of the cells and tissues of the body proceeds, or in other words, the constancy of the internal environment is maintained.
It should be noted that in humans, the nervous system plays a leading role in the regulation of the vital activity of the body.
Thus, the human body is a single, integral, complex, self-regulating and self-developing biological system with certain reserve capabilities. Wherein
know that the ability to perform physical work can increase many times, but up to a certain limit. Whereas mental activity actually has no restrictions in its development.
Systematic muscular activity allows, by improving physiological functions, to mobilize the reserves of the body, the existence of which many do not even know. It should be noted that there is a reverse process, a decrease in the functional capabilities of the body and accelerated aging with a decrease in physical activity.
In the course of physical exercises, the higher nervous activity and the functions of the central nervous system are improved. neuromuscular. cardiovascular, respiratory, excretory and other systems, metabolism and energy, as well as the system of their neurohumoral regulation.
The human body, using the properties of self-regulation of internal processes under external influence, realizes the most important property - adaptation to changing external conditions, which is a determining factor in the ability to develop physical qualities and motor skills during training.
Let us consider in more detail the nature of physiological changes in the process of training.
Physical activity leads to diverse changes in metabolism, the nature of which depends on the duration, power of work and the number of muscles involved. During physical activity, catabolic processes, mobilization and use of energy substrates predominate, and intermediate metabolic products accumulate. The rest period is characterized by the predominance of anabolic processes, the accumulation of a reserve of nutrients, and increased protein synthesis.
The recovery rate depends on the magnitude of the changes that occur during operation, that is, on the magnitude of the load.
During the rest period, the metabolic changes that occurred during muscle activity are eliminated. If during physical activity catabolic processes, mobilization and use of energy substrates predominate, there is an accumulation of intermediate metabolic products, then the rest period is characterized by the predominance of anabolic processes, the accumulation of a reserve of nutrients, and increased protein synthesis.
In the post-working period, the intensity of aerobic oxidation increases, oxygen consumption is increased, i.e. oxygen debt is eliminated. The substrate for oxidation is the intermediate metabolic products formed during muscle activity, lactic acid, ketone bodies, keto acids. Carbohydrate reserves during physical work, as a rule, are significantly reduced, so fatty acids become the main substrate for oxidation. Due to the increased use of lipids during the recovery period, the respiratory quotient decreases.
The recovery period is characterized by increased protein biosynthesis, which is inhibited during physical work, and the formation and excretion of the end products of protein metabolism (urea, etc.) from the body also increases.
The recovery rate depends on the magnitude of the changes that occur during operation, i.e. on the magnitude of the load, which is schematically shown in Fig. one
Fig.1 Scheme of the processes of expenditure and recovery of sources
energy during muscular activity of military intensity
Restoration of changes that occur under the influence of loads of low and medium intensity is slower than after loads of increased and maximum intensity, which is explained by deeper changes during the period of work. After increased intensity loads, the observed metabolic rate, substances not only reaches the initial level, but also exceeds it. This increase above the initial level is called super recovery (super compensation). It is registered only when the load exceeds a certain level in value, i.e. when the resulting changes in metabolism affect the genetic apparatus of the cell. The severity of over-recovery and its duration are directly dependent on the intensity of the load.
The phenomenon of overpowering is an important mechanism of adaptation (of an organ) to changing conditions of functioning and is important for understanding the biochemical foundations of sports training. It should be noted that as a general biological pattern, it extends not only to the accumulation of energy material, but also to the synthesis of proteins, which, in particular, manifests itself in the form of working hypertrophy of skeletal muscles, the heart muscle. After an intense load, the synthesis of a number of enzymes increases (enzyme induction), the concentration of creatine phosphate and myoglobin increases, and a number of other changes occur.
It has been established that active muscular activity causes an increase in the activity of the cardiovascular, respiratory and other body systems. In any human activity, all organs and systems of the body act in concert, in close unity. This relationship is carried out with the help of the nervous system and humoral (fluid) regulation.
The nervous system regulates the activity of the body through bioelectric impulses. The main nervous processes are excitation and inhibition that occur in nerve cells. Excitation- the active state of nerve cells, when they transmit silt, they themselves direct nerve impulses to other cells: nerve, muscle, glandular and others. Braking- the state of nerve cells, when their activity is aimed at recovery. Sleep, for example, is a state of the nervous system, when the vast majority of nerve cells of the central nervous system are inhibited.
Humoral regulation is carried out through the blood by means of special chemicals (hormones) secreted by the endocrine glands, the concentration ratio CO2 and O2 through other mechanisms. For example, in the pre-launch state, when intense physical activity is expected, the endocrine glands (adrenal glands) secrete a special hormone, adrenaline, into the blood, which enhances the activity of the cardiovascular system.
Humoral and nervous regulation are carried out in unity. The leading role is assigned to the central nervous system, the brain, which is, as it were, the central headquarters for controlling the vital activity of the organism.
2.10.1. Reflex nature and reflex mechanisms of motor activity
The nervous system operates on the principle of a reflex. Inherited reflexes, inherent in the nervous system from birth, in its structure, in the connections between nerve cells, are called unconditioned reflexes. Combining in long chains, unconditioned reflexes are the basis of instinctive behavior. In humans and in higher animals, behavior is based on conditioned reflexes developed in the process of life on the basis of unconditioned reflexes.
Sports and labor activity of a person, including the mastery of motor skills, is carried out according to the principle of the relationship of conditioned reflexes and dynamic stereotypes with unconditioned reflexes.
To perform clear targeted movements, it is necessary to continuously receive signals to the central nervous system about the functional state of the muscles, about the degree of their contraction, tension and relaxation, about the posture of the body, about the position of the joints and the angle of bend in them.
All this information is transmitted from the receptors of the sensory systems and especially from the receptors of the motor sensory system, from the so-called proprioreceptors, which are located in muscle tissue, fascia, articular bags and tendons.
From these receptors, by the feedback principle and by the reflex mechanism, the CNS receives complete information about the performance of a given motor action and about its comparison with a given program.
Each, even the simplest movement, needs constant correction, which is provided by information coming from proprioceptors and other sensory systems. With repeated repetition of a motor action, impulses from receptors reach the motor centers in the central nervous system, which accordingly change their impulses going to the muscles in order to improve the movement being learned.
Thanks to such a complex reflex mechanism, motor activity is improved.
Physiological regulation is the control of body functions in order to adapt it to environmental conditions. The regulation of body functions is the basis for ensuring the constancy of the internal environment of the body and its adaptation to changing conditions of existence and is carried out according to the principle of self-regulation through the formation of functional systems. The function of systems and the organism as a whole is called an activity aimed at maintaining the integrity and properties of the system. Functions are characterized quantitatively and qualitatively. The basis of physiological regulation is the transmission and processing of information. The term "information" refers to any communication about facts and events occurring in the environment and the human body. Self-regulation is understood as such a type of regulation, when the deviation of the controlled parameter is a stimulus for its restoration. To implement the principle of self-regulation, the interaction of the following components of functional systems is necessary.
Regulated parameter (object of regulation, constant).
Control devices that monitor the deviation of this parameter under the influence of external and internal factors.
Regulatory apparatuses that provide a directed effect on the activity of organs, on which the restoration of a deviated parameter depends.
Execution devices - organs and systems of organs, the change in the activity of which in accordance with regulatory influences leads to the restoration of the initial value of the parameter. "Reverse afferentation carries information to the regulatory apparatus about the achievement or non-achievement of a useful result, about the return or non-return of the deviated parameter to the norm. Thus, the regulation of functions is carried out by a system that consists of separate elements: a control device (CNS, endocrine cell), communication channels ( nerves, liquid internal environment), sensors that perceive the action of factors of the external and internal environment (receptors), structures that perceive information from output channels (cell receptors) and executive organs.
The regulatory system in the body is a three-level structure. The first level of regulation consists of relatively autonomous local systems that maintain constants. The second level of the regulation system provides adaptive responses in connection with changes in the internal environment; at this level, the optimal mode of operation of physiological systems is provided for adapting the body to the external environment. The third level of regulation is implemented by the behavioral reactions of the organism and ensures the optimization of its vital activity.
There are four types of regulation: mechanical, humoral, nervous, neurohumoral.
Physical (mechanical) regulation It is realized through mechanical, electrical, optical, sound, electromagnetic, thermal and other processes (for example, filling the heart cavities with an additional volume of blood leads to a greater degree of stretching of their walls and to a stronger contraction of the myocardium). The most reliable mechanisms of regulation are local. They are realized through the physicochemical interaction of the structures of the organ. For example, in a working muscle, as a result of the release of chemical metabolites and heat by myocytes, the blood vessels expand, which is accompanied by an increase in the volumetric blood flow velocity and an increase in the supply of myocytes with nutrients and oxygen. Local regulation can be carried out with the help of biologically active substances (histamine), tissue hormones (prostaglandins).
Humoral regulation It is carried out through the liquid media of the body (blood (humor), lymph, intercellular, cerebrospinal fluid) with the help of various biologically active substances that are secreted by specialized cells, tissues or organs. This type of regulation can be carried out at the level of organ structures - local self-regulation, or provide generalized effects through the system of hormonal regulation. The blood receives chemicals that are formed in specialized tissues and have specific functions. Among these substances are distinguished: metabolites, mediators, hormones. They can act locally or remotely. For example, ATP hydrolysis products, the concentration of which increases with an increase in the functional activity of cells, cause the expansion of blood vessels and improve the trophism of these cells. Especially important role is played by hormones - products of secretion of special, endocrine organs. The endocrine glands include: the pituitary gland, the thyroid and parathyroid glands, the islet apparatus of the pancreas, the cortex and medulla of the adrenal glands, the gonads, the placenta and the pineal gland. Hormones affect metabolism, stimulate morphogenesis processes, differentiation, growth, metamorphosis of cells, include a certain activity of the executive organs, change the intensity of the activity of the executive organs and tissues. The humoral pathway of regulation acts relatively slowly, the rate of response depends on the rate of formation and secretion of the hormone, its penetration into the lymph and blood, and the rate of blood flow. The local action of the hormone is determined by the presence of a specific receptor for it. The duration of the action of the hormone depends on the rate of its destruction in the body. In various cells of the body, including the brain, neuropeptides are formed that act on the behavior of the body, a number of different functions and regulate the secretion of hormones.
Nervous regulation It is carried out through the nervous system, based on the processing of information by neurons and its transmission along the nerves. Has the following features:
Greater speed of development of action;
Communication accuracy;
High specificity - a strictly defined number of components required at the moment participate in the reaction.
Nervous regulation is carried out quickly, with the direction of the signal to a specific addressee. The transmission of information (action potentials of neurons) is carried out at a speed of up to 80-120 m/s without a decrease in amplitude and loss of energy. The somatic and vegetative functions of the body are subject to nervous regulation. The basic principle of nervous regulation is reflex. The nervous mechanism of regulation phylogenetically arose later than the local and humoral and provides high accuracy, speed and reliability of the response. It is the most perfect mechanism of regulation.
neurohumoral correlation. In the process of evolution, the nervous and humoral types of correlations were combined into a neurohumoral form, when the urgent involvement of organs in the process of action by means of nervous correlation is supplemented and prolonged by humoral factors.
Nervous and humoral correlations play a leading role in the unification (integration) of the constituent parts (components) of the body into a single organism. At the same time, they seem to complement each other with their own characteristics. The humoral connection has a generalized character. It is simultaneously implemented throughout the body. The nervous connection has a directed character, it is the most selective and is realized in each specific case mainly at the level of certain components of the body.
Creator bonds provide the exchange of macromolecules between cells, which are capable of exerting a regulatory influence on the processes of metabolism, differentiation, growth, development, and functioning of cells and tissues. Keylons, proteins that inhibit the synthesis of nucleic acids and cell division, are influenced by creative bonds.
Metabolites by the feedback mechanism affect intracellular metabolism and cell functions and the functioning of adjacent structures. For example, during intense muscle work, lactic and pyruvic acids, which are formed in the muscle cell under conditions of oxygen deficiency, lead to the expansion of muscle microvessels, to an increase in the flow of blood, nutrients and oxygen, which improves the nutrition of muscle cells. At the same time, they stimulate the metabolic pathways of their use, reduce the contractility of the muscle.
The neuroendocrine system ensures that the metabolic, physical functions and behavioral reactions of the body correspond to environmental conditions, supports the processes of differentiation, growth, development, and regeneration of cells; generally contribute to the preservation and development of both the individual and the biological species as a whole. Dual (nervous and endocrine) regulation provides, through the mechanism of duplication, the reliability of regulation, the high rate of response through the nervous system and the duration of the response in time through the release of hormones. Phylogenetically, the most ancient hormones are produced by nerve cells; the chemical signal and the nerve impulse are often interconvertible. Hormones, being neuromodulators, affect the effects in the central nervous system of many mediators (gastrin, cholecystokinin, VIP, GIP, neurotensin, bombesin, substance P, opiomelanocortins - ACTH, beta-, gamma-lipotropins, alpha-, beta-, gamma-endorphins, prolactin, somatotropin). Hormone-producing neurons have been described.
Nervous and humoral regulation is based on the principle of a circular connection, which was shown as a priority in biological systems by the Soviet physiologist P.K. Anokhin. Positive and negative feedbacks provide an optimal level of functioning - strengthening weak responses and limiting superstrong ones.
The division of regulatory mechanisms into nervous and humoral is conditional. In the body, these mechanisms are inseparable.
1) Information about the state of the external and internal environment, as a rule, is perceived by the elements of the nervous system, and after processing in neurons, both the nervous and humoral pathways of regulation can be used as executive organs.
2) The activity of the endocrine glands is controlled by the nervous system. In turn, the metabolism, development and differentiation of neurons is carried out under the influence of hormones.
3) Action potentials at the points of contact between the neuron and the working cell cause the secretion of a mediator, which, through the humoral link, changes the function of the cell. Thus, in the body there is a single neurohumoral regulation with the priority of the nervous system. The body responds to the action of each stimulus with a complex biological reaction as a whole. This is achieved by the interaction of all systems, tissues and cells of the body. Interaction is provided by local, humoral and nervous mechanisms of regulation
The human nervous system is divided into central (brain and spinal cord) and peripheral. The central nervous system ensures the individual adaptation of the organism to the environment, adaptation of the organism, the behavior of the organism in accordance with the constitution and its needs, ensures the integration and unification of organs into a single whole based on the perception, evaluation, comparison, analysis of information coming from the external and internal environment of the body . The peripheral nervous system provides tissue trophism and has a direct impact on the structure and functional activity of organs.
The most important concepts of the theory of physiological regulation.
Before considering the mechanisms of neurohumoral regulation, let us dwell on the most important concepts of this branch of physiology. Some of them are developed by cybernetics. Knowledge of such concepts facilitates the understanding of the regulation of physiological functions and the solution of a number of problems in medicine.
Physiological function- a manifestation of the vital activity of an organism or its structures (cells, organs, systems of cells and tissues), aimed at preserving life and fulfilling genetically and socially determined programs.
System- a set of interacting elements that perform a function that cannot be performed by one individual element.
Element - structural and functional unit of the system.
Signal - various types of matter and energy that transmit information.
Information information, messages transmitted through communication channels and perceived by the body.
Stimulus- a factor of the external or internal environment, the impact of which on the receptor formations of the body causes a change in the processes of vital activity. Irritants are divided into adequate and inadequate. to perception adequate stimuli the body's receptors are adapted and activated at a very low energy of the influencing factor. For example, to activate the receptors of the retina (rods and cones), 1-4 quantums of light are enough. inadequate are irritants, to the perception of which the sensitive elements of the body are not adapted. For example, cones and rods of the retina of the eye are not adapted to the perception of mechanical influences and do not provide the appearance of a sensation even with a significant impact on them. Only with a very large force of impact (impact) can they be activated and a sensation of light arise.
Irritants are also subdivided according to their strength into subthreshold, threshold and suprathreshold. Strength subthreshold stimuli insufficient for the occurrence of a registered response of the body or its structures. threshold stimulus called such, the minimum force of which is sufficient for the occurrence of a pronounced response. Suprathreshold stimuli are more powerful than threshold stimuli.
Stimulus and signal are similar but not unambiguous concepts. One and the same stimulus may have a different signal value. For example, the squeak of a hare may be a signal that warns of the danger of relatives, but for a fox, the same sound is a signal of the possibility of obtaining food.
Irritation - the impact of environmental or internal factors on the structures of the body. It should be noted that in medicine the term "irritation" is sometimes used in another sense - to refer to the response of the body or its structures to the action of the stimulus.
Receptors molecular or cellular structures that perceive the action of external or internal environmental factors and transmit information about the signal value of the stimulus to subsequent links in the regulatory circuit.
The concept of receptors is considered from two points of view: from molecular biological and morphofunctional. In the latter case, we speak of sensory receptors.
FROM molecular biological point of view, receptors are specialized protein molecules embedded in the cell membrane or located in the cytosol and nucleus. Each type of such receptors is able to interact only with strictly defined signal molecules - ligands. For example, for the so-called adrenoreceptors, the ligands are the hormone molecules of adrenaline and norepinephrine. These receptors are embedded in the membranes of many body cells. The role of ligands in the body is performed by biologically active substances: hormones, neurotransmitters, growth factors, cytokines, prostaglandins. They perform their signaling function, being in biological fluids in very small concentrations. For example, the content of hormones in the blood is found within 10 -7 -10 - 10 mol / l.
FROM morphofunctional point of view, receptors (sensory receptors) are specialized cells or nerve endings, the function of which is to perceive the action of stimuli and ensure the occurrence of excitation in nerve fibers. In this sense, the term "receptor" is most often used in physiology when it comes to the regulation provided by the nervous system.
The set of sensory receptors of the same type and the area of the body in which they are concentrated are called receptor field.
The function of sensory receptors in the body is performed by:
specialized nerve endings. They may be free, not sheathed (eg skin pain receptors) or sheathed (eg skin tactile receptors);
specialized nerve cells (neurosensory cells). In humans, such sensory cells are found in the layer of epithelium lining the surface of the nasal cavity; they provide the perception of odorous substances. In the retina of the eye, neurosensory cells are represented by cones and rods that perceive light rays;
3) specialized epithelial cells are cells developing from epithelial tissue that have acquired a high sensitivity to the action of certain types of stimuli and can transmit information about these stimuli to nerve endings. Such receptors are present in the inner ear, the taste buds of the tongue and the vestibular apparatus, providing the ability to perceive sound waves, taste sensations, body position and movement, respectively.
Regulation constant monitoring and necessary correction of the functioning of the system and its individual structures in order to achieve a useful result.
Physiological regulation- a process that ensures the preservation of relative constancy or a change in the desired direction of homeostasis and vital functions of the body and its structures.
The physiological regulation of the vital functions of the body is characterized by the following features.
The presence of closed control loops. The simplest regulatory circuit (Fig. 2.1) includes blocks: adjustable parameter(e.g. blood glucose level, blood pressure value), control device- in a whole organism it is a nerve center, in a separate cell - a genome, effectors- bodies and systems that, under the influence of signals from the control device, change their work and directly affect the value of the controlled parameter.
The interaction of individual functional blocks of such a regulatory system is carried out through direct and feedback channels. Through direct communication channels, information is transmitted from the control device to effectors, and through feedback channels - from receptors (sensors) that control
Rice. 2.1. Closed Loop Diagram
that determine the value of the controlled parameter - to the control device (for example, from skeletal muscle receptors - to the spinal cord and brain).
Thus, feedback (it is also called reverse afferentation in physiology) ensures that the control device receives a signal about the value (state) of the controlled parameter. It provides control over the response of effectors to the control signal and the result of the action. For example, if the purpose of the movement of a human hand was to open a textbook of physiology, then the feedback is carried out by conducting impulses along the afferent nerve fibers from the receptors of the eyes, skin and muscles to the brain. Such impulsation provides the possibility of tracking the movements of the hand. Thanks to this, the nervous system can carry out movement correction to achieve the desired result of the action.
With the help of feedback (reverse afferentation), the regulatory circuit is closed, its elements are combined into a closed circuit - a system of elements. Only in the presence of a closed control loop is it possible to implement stable regulation of homeostasis parameters and adaptive reactions.
Feedback is divided into negative and positive. In the body, the vast majority of feedbacks are negative. This means that under the influence of the information coming through their channels, the regulatory system returns the deviated parameter to its original (normal) value. Thus, negative feedback is necessary to maintain the stability of the level of the regulated indicator. In contrast, positive feedback contributes to changing the value of the controlled parameter, transferring it to a new level. So, at the beginning of an intense muscular load, impulses from skeletal muscle receptors contribute to the development of an increase in the level of arterial blood pressure.
The functioning of neurohumoral regulatory mechanisms in the body is not always aimed only at maintaining homeostatic constants at an unchanged, strictly stable level. In a number of cases, it is vital for the body that the regulatory systems restructure their work and change the value of the homeostatic constant, change the so-called "set point" of the controlled parameter.
Set point(English) set point). This is the level of the controlled parameter at which the regulatory system seeks to maintain the value of this parameter.
Understanding the presence and direction of changes in the homeostatic regulation set point helps to determine the cause of pathological processes in the body, predict their development and find the right way of treatment and prevention.
Consider this using the example of assessing the body's temperature reactions. Even when a person is healthy, the temperature of the core of the body during the day fluctuates between 36 ° C and 37 ° C, and in the evening hours it is closer to 37 ° C, at night and in the early morning - to 36 ° C. This indicates the presence of a circadian rhythm of change in the value of the set point of thermoregulation. But the presence of changes in the set point of the temperature of the core of the body in a number of human diseases manifests itself especially clearly. For example, with the development of infectious diseases, the thermoregulatory centers of the nervous system receive a signal about the appearance of bacterial toxins in the body and restructure their work in such a way as to increase the level of body temperature. Such a reaction of the body to the introduction of infection is developed phylogenetically. It is useful, since at elevated temperatures the immune system functions more actively, and the conditions for the development of infection worsen. That is why it is not always necessary to prescribe antipyretics when fever develops. But since a very high temperature of the core of the body (more than 39 ° C, especially in children) can be dangerous for the body (primarily in terms of damage to the nervous system), the doctor must make an individual decision in each individual case. If at a body temperature of 38.5 - 39 ° C there are signs such as muscle tremors, chills, when a person wraps himself in a blanket, seeks to warm up, then it is clear that the mechanisms of thermoregulation continue to mobilize all sources of heat production and ways to save heat in the body. This means that the set point has not yet been reached and in the near future the body temperature will rise, reaching dangerous limits. But if, at the same temperature, the patient develops profuse sweating, muscle tremors disappear and he opens up, then it is clear that the set point has already been reached and the mechanisms of thermoregulation will prevent a further increase in temperature. In such a situation, the doctor for a certain time in some cases may refrain from prescribing antipyretics.
Levels of regulatory systems. There are the following levels:
subcellular (for example, self-regulation of chains of biochemical reactions combined into biochemical cycles);
cellular - regulation of intracellular processes with the help of biologically active substances (autocrinia) and metabolites;
tissue (paracrinia, creative connections, regulation of cell interaction: adhesion, integration into tissue, synchronization of division and functional activity);
organ - self-regulation of individual organs, their functioning as a whole. Such regulation is carried out both due to humoral mechanisms (paracrinia, creative connections), and nerve cells, the bodies of which are located in the intraorgan autonomic ganglia. These neurons interact to form intraorganic reflex arcs. At the same time, the regulatory influences of the central nervous system on the internal organs are also realized through them;
organismic regulation of homeostasis, integrity of the organism, formation of regulatory functional systems that provide appropriate behavioral responses, adaptation of the organism to changes in environmental conditions.
Thus, there are many levels of regulatory systems in the body. The simplest systems of the body are combined into more complex ones capable of performing new functions. In this case, simple systems, as a rule, obey control signals from more complex systems. This subordination is called the hierarchy of regulatory systems.
The mechanisms for implementing these regulations will be discussed in more detail below.
Unity and distinctive features of nervous and humoral regulation. The mechanisms of regulation of physiological functions are traditionally divided into nervous and humoral.
although in reality they form a single regulatory system that ensures the maintenance of homeostasis and the adaptive activity of the body. These mechanisms have numerous connections both at the level of functioning of nerve centers and in the transmission of signal information to effector structures. Suffice it to say that during the implementation of the simplest reflex as an elementary mechanism of nervous regulation, the transmission of signaling from one cell to another is carried out through humoral factors - neurotransmitters. The sensitivity of sensory receptors to the action of stimuli and the functional state of neurons are changed under the influence of hormones, neurotransmitters, a number of other biologically active substances, as well as the simplest metabolites and mineral ions (K + Na + CaCI -). In turn, the nervous system can trigger or correct humoral regulation. Humoral regulation in the body is under the control of the nervous system.
Features of nervous and humoral regulation in the body. Humoral mechanisms are phylogenetically older; they are present even in unicellular animals and acquire great diversity in multicellular organisms, and especially in humans.
The nervous mechanisms of regulation were formed phylogenetically later and are formed gradually in human ontogenesis. Such regulation is possible only in multicellular structures that have nerve cells that combine into nerve circuits and make up reflex arcs.
Humoral regulation is carried out by the distribution of signal molecules in body fluids according to the principle "everyone, everything, everyone", or the principle of "radio communication"
Nervous regulation is carried out according to the principle of "letter with an address", or "telegraph communication". Signaling is transmitted from the nerve centers to strictly defined structures, for example, to precisely defined muscle fibers or their groups in a particular muscle. Only in this case purposeful, coordinated human movements are possible.
Humoral regulation, as a rule, is carried out more slowly than nervous regulation. The speed of the signal (action potential) in fast nerve fibers reaches 120 m / s, while the speed of transport of the signal molecule
kula with blood flow in the arteries approximately 200 times, and in the capillaries - a thousand times less.
The arrival of a nerve impulse to an effector organ almost instantly causes a physiological effect (for example, contraction of a skeletal muscle). The response to many hormonal signals is slower. For example, the manifestation of a response to the action of thyroid hormones and the adrenal cortex occurs after tens of minutes and even hours.
Humoral mechanisms are of primary importance in the regulation of metabolic processes, the rate of cell division, the growth and specialization of tissues, puberty, and adaptation to changing environmental conditions.
The nervous system in a healthy organism influences all humoral regulation and corrects them. However, the nervous system has its own specific functions. It regulates vital processes that require quick reactions, provides the perception of signals coming from the sensory receptors of the sense organs, skin and internal organs. Regulates the tone and contractions of the skeletal muscles, which ensure the maintenance of the posture and the movement of the body in space. The nervous system provides the manifestation of such mental functions as sensation, emotions, motivation, memory, thinking, consciousness, regulates behavioral reactions aimed at achieving a useful adaptive result.
Despite the functional unity and numerous interrelations of nervous and humoral regulations in the body, for the sake of convenience in studying the mechanisms for implementing these regulations, we will consider them separately.
Characterization of the mechanisms of humoral regulation in the body. Humoral regulation is carried out due to the transmission of signals with the help of biologically active substances through the liquid media of the body. The biologically active substances of the body include: hormones, neurotransmitters, prostaglandins, cytokines, growth factors, endothelium, nitric oxide and a number of other substances. To perform their signaling function, a very small amount of these substances is sufficient. For example, hormones perform their regulatory role when their concentration in the blood is in the range of 10 -7 -10 0 mol / l.
Humoral regulation is divided into endocrine and local.
Endocrine regulation are carried out due to the functioning of the endocrine glands (endocrine glands), which are specialized organs that secrete hormones. Hormones- biologically active substances produced by the endocrine glands, carried by the blood and having specific regulatory effects on the vital activity of cells and tissues. A distinctive feature of endocrine regulation is that the endocrine glands secrete hormones into the blood and in this way these substances are delivered to almost all organs and tissues. However, the response to the action of the hormone can only be from those cells (targets) on the membranes, in the cytosol or nucleus of which there are receptors for the corresponding hormone.
Distinctive feature local humoral regulation is that the biologically active substances produced by the cell do not enter the bloodstream, but act on the cell producing them and its immediate environment, spreading through the intercellular fluid due to diffusion. Such regulation is subdivided into the regulation of metabolism in the cell due to metabolites, autocrinia, paracrinia, juxtacrinia, interactions through intercellular contacts.
Regulation of metabolism in the cell due to metabolites. Metabolites are the end and intermediate products of metabolic processes in the cell. The participation of metabolites in the regulation of cellular processes is due to the presence in the metabolism of chains of functionally related biochemical reactions - biochemical cycles. It is characteristic that already in such biochemical cycles there are the main signs of biological regulation, the presence of a closed control loop and negative feedback, which ensures the closure of this loop. For example, chains of such reactions are used in the synthesis of enzymes and substances involved in the formation of adenosine triphosphate (ATP). ATP is a substance in which energy is accumulated, which is easily used by cells for a variety of life processes: movement, synthesis of organic substances, growth, transport of substances through cell membranes.
autocrine mechanism. With this type of regulation, the signal molecule synthesized in the cell is released through
Receptor r t Endocrine
about? m ooo
Augocrinia Paracrinia Yuxtacrinia t
Rice. 2.2. Types of humoral regulation in the body
cell membrane into the intercellular fluid and binds to the receptor on the outer surface of the membrane (Fig. 2.2). Thus, the cell reacts to the signal molecule synthesized in it - the ligand. The attachment of a ligand to a receptor on the membrane causes the activation of this receptor, and it triggers a whole cascade of biochemical reactions in the cell, which provide a change in its vital activity. Autocrine regulation is often used by cells of the immune and nervous systems. This autoregulatory pathway is necessary to maintain a stable level of secretion of certain hormones. For example, in preventing excessive secretion of insulin by P-cells of the pancreas, the inhibitory effect of the hormone secreted by them on the activity of these cells is important.
paracrine mechanism. It is carried out by the secretion of signal molecules by the cell, which go into the intercellular fluid and affect the vital activity of neighboring cells (Fig. 2.2). A distinctive feature of this type of regulation is that in signal transmission there is a stage of diffusion of the ligand molecule through the intercellular fluid from one cell to other neighboring cells. Thus, cells of the pancreas that secrete insulin affect the cells of this gland that secrete another hormone, glucagon. Growth factors and interleukins affect cell division, prostaglandins - on smooth muscle tone, Ca 2+ mobilization. This type of signaling is important in regulating tissue growth during embryonic development, wound healing, for the growth of damaged nerve fibers and in the transmission of excitation in synapses.
Recent studies have shown that some cells (especially nerve cells) must constantly receive specific signals in order to maintain their vital activity.
L1 from neighboring cells. Among these specific signals, growth factors (NGFs) are especially important. In the absence of exposure to these signaling molecules for a long time, nerve cells start a program of self-destruction. This mechanism of cell death is called apoptosis.
Paracrine regulation is often used simultaneously with autocrine regulation. For example, during the transmission of excitation in synapses, the signal molecules released by the nerve ending bind not only to the receptors of the neighboring cell (on the postsynaptic membrane), but also to the receptors on the membrane of the same nerve ending (i.e., the presynaptic membrane).
Juxtacrine mechanism. It is carried out by transferring signal molecules directly from the outer surface of the membrane of one cell to the membrane of another. This occurs under the condition of direct contact (attachment, adhesive bonding) of the membranes of two cells. Such attachment occurs, for example, when leukocytes and platelets interact with the endothelium of blood capillaries in a place where there is an inflammatory process. On the membranes lining the capillaries of cells, signaling molecules appear at the site of inflammation, which bind to receptors of certain types of leukocytes. This connection leads to activation of the attachment of leukocytes to the surface of the blood vessel. This can be followed by a whole complex of biological reactions that ensure the transition of leukocytes from the capillary to the tissue and suppression of the inflammatory reaction by them.
Interactions through intercellular contacts. Carried out through intermembrane connections (insert disks, nexuses). In particular, the transmission of signaling molecules and some metabolites through gap junctions - nexuses - is very common. During the formation of nexuses, special protein molecules (connexons) of the cell membrane are combined in 6 pieces so that they form a ring with a pore inside. On the membrane of a neighboring cell (exactly opposite), the same ring-shaped formation with a pore is formed. Two central pores unite to form a channel penetrating the membranes of neighboring cells. The channel width is sufficient for the passage of many biologically active substances and metabolites. Ca 2+ ions pass freely through the nexus, being powerful regulators of intracellular processes.
Due to their high electrical conductivity, nexuses contribute to the propagation of local currents between neighboring cells and the formation of the functional unity of the tissue. Such interactions are especially pronounced in the cells of the cardiac muscle and smooth muscles. Violation of the state of intercellular contacts leads to pathology of the heart, changes
increase in vascular muscle tone, weakness of uterine contraction, and changes in a number of other regulations.
Cell-to-cell contacts that serve to strengthen the physical connection between membranes are called tight junctions and adhesive belts. Such contacts may take the form of a circular belt passing between the side surfaces of the cell. The compaction and increase in the strength of these compounds is ensured by the attachment of myosin, actinin, tropomyosin, vinculin, etc. proteins to the surface of the membranes. Tight junctions contribute to the integration of cells into tissue, their adhesion and tissue resistance to mechanical stress. They are also involved in the formation of barrier formations in the body. Tight junctions are especially pronounced between the endothelium lining the vessels of the brain. They reduce the permeability of these vessels for substances circulating in the blood.
Cellular and intracellular membranes play an important role in all humoral regulation involving specific signaling molecules. Therefore, to understand the mechanism of humoral regulation, it is necessary to know the elements of the physiology of cell membranes.
Rice. 2.3. Scheme of the structure of the cell membrane
Carrier protein
(secondary-active
transport)
Membrane protein
Protein PKC
double layer of phospholipids
Antigens
Extracellular surface
Intracellular environment
Features of the structure and properties of cell membranes. All cell membranes are characterized by one principle of structure (Fig. 2.3). They are based on two layers of lipids (fat molecules, most of which are phospholipids, but there are also cholesterol and glycolipids). Membrane lipid molecules have a head (a site that attracts water and seeks to interact with it, called a guideprofile) and a tail that is hydrophobic (repels water molecules, avoids their proximity). As a result of this difference in the properties of the head and tail of lipid molecules, when they hit the surface of the water, they line up in rows: head to head, tail to tail and form a double layer in which the hydrophilic heads face the water, and the hydrophobic tails face each other. The tails are inside this double layer. The presence of the lipid layer forms a closed space, isolates the cytoplasm from the surrounding aquatic environment and creates an obstacle for the passage of water and substances soluble in it through the cell membrane. The thickness of such a lipid bilayer is about 5 nm.
Membrane also contains proteins. Their molecules by volume and mass are 40-50 times larger than the molecules of membrane lipids. Due to proteins, the thickness of the membrane reaches? -10 nm. Despite the fact that the total masses of proteins and lipids in most membranes are almost equal, the number of protein molecules in the membrane is ten times less than that of lipid molecules. Typically, protein molecules are scattered. They are, as it were, dissolved in the membrane, they can move in it and change their position. This was the reason that the structure of the membrane was called liquid mosaic. Lipid molecules can also move along the membrane and even jump from one lipid layer to another. Consequently, the membrane has signs of fluidity and, at the same time, has the property of self-assembly, can recover from damage due to the property of lipid molecules to line up in a double lipid layer.
Protein molecules can penetrate the entire membrane so that their end sections protrude beyond its transverse limits. Such proteins are called transmembrane or integral. There are also proteins that are only partially immersed in the membrane or located on its surface.
Cell membrane proteins perform numerous functions. For the implementation of each function, the cell genome provides the trigger for the synthesis of a specific protein. Even in a relatively simple erythrocyte membrane, there are about 100 different proteins. Among the most important functions of membrane proteins are: 1) receptor - interaction with signaling molecules and signal transmission into the cell; 2) transport - the transfer of substances through membranes and ensuring the exchange between the cytosol and the environment. There are several types of protein molecules (translocases) that provide transmembrane transport. Among them are proteins that form channels that penetrate the membrane and through them diffusion of certain substances occurs between the cytosol and the extracellular space. Such channels are most often ion-selective; pass ions of only one substance. There are also channels whose selectivity is less, for example, they pass Na + and K +, K + and C1 ~ ions. There are also carrier proteins that ensure the transport of a substance across the membrane by changing its position in this membrane; 3) adhesive - proteins together with carbohydrates are involved in the implementation of adhesion (sticking together, gluing cells during immune reactions, combining cells into layers and tissues); 4) enzymatic - some proteins embedded in the membrane act as catalysts for biochemical reactions, the course of which is possible only in contact with cell membranes; 5) mechanical - proteins provide strength and elasticity of membranes, their connection with the cytoskeleton. For example, in erythrocytes, this role is played by the spectrin protein, which is attached to the inner surface of the erythrocyte membrane in the form of a mesh structure and has a connection with intracellular proteins that make up the cytoskeleton. This gives the erythrocytes elasticity, the ability to change and restore shape when passing through the blood capillaries.
Carbohydrates make up only 2-10% of the membrane mass, their amount in different cells is variable. Thanks to carbohydrates, some types of intercellular interactions are carried out, they take part in the recognition of foreign antigens by the cell and, together with proteins, create a kind of antigenic structure of the surface membrane of their own cell. By such antigens, cells recognize each other, unite into tissue and stick together for a short time to transmit signaling molecules. Compounds of proteins with sugars are called glycoproteins. If carbohydrates are combined with lipids, then such molecules are called glycolipids.
Due to the interaction of the substances included in the membrane and the relative orderliness of their arrangement, the cell membrane acquires a number of properties and functions that cannot be reduced to a simple sum of the properties of the substances that form it.
Functions of cell membranes and mechanisms for their implementation
To the mainfunctions of cell membranes attributed to the creation of a membrane (barrier) that separates the cytosol from
^pressing environment, And demarcation And the shape of the cell; about the provision of intercellular contacts, accompanied by panie membranes (adhesion). Intercellular adhesion is important ° I combine the same type of cells into tissue, the formation of gis- hematic barriers, implementation of immune reactions; And interaction with them, as well as the transmission of signals into the cell; 4) providing membrane proteins-enzymes for catalysis of biochemical reactions, going in the near-membrane layer. Some of these proteins also act as receptors. The binding of the ligand to the stakimireceptor activates its enzymatic properties; 5) Ensuring membrane polarization, generating a difference electrical potentials between outdoor And internal side membranes; 6) creation of the immune specificity of the cell due to the presence of antigens in the membrane structure. The role of antigens, as a rule, is performed by sections of protein molecules protruding above the membrane surface and carbohydrate molecules associated with them. Immune specificity matters when cells combine into tissue and interact with immune surveillance cells in the body; 7) ensuring the selective permeability of substances through the membrane and their transport between the cytosol and the environment (see below).
The above list of functions of cell membranes indicates that they take a multifaceted part in the mechanisms of neurohumoral regulation in the body. Without knowledge of a number of phenomena and processes provided by membrane structures, it is impossible to understand and consciously perform certain diagnostic procedures and therapeutic measures. For example, for the correct use of many medicinal substances, it is necessary to know to what extent each of them penetrates from the blood into the tissue fluid and into the cytosol.
diffuse and I and transport of substances through cellular membranes. The transition of substances through cell membranes is carried out due to different types of diffusion, or active
transport.
simple diffusion is carried out due to concentration gradients of a certain substance, electric charge or osmotic pressure between the sides of the cell membrane. For example, the average content of sodium ions in blood plasma is 140 mM / l, and in erythrocytes - approximately 12 times less. This concentration difference (gradient) creates a driving force that ensures the transition of sodium from plasma to red blood cells. However, the rate of such a transition is low, since the membrane has a very low permeability for Na + ions. The permeability of this membrane for potassium is much greater. The energy of cellular metabolism is not spent on the processes of simple diffusion. The increase in the rate of simple diffusion is directly proportional to the concentration gradient of the substance between the sides of the membrane.
Facilitated diffusion, like a simple one, it follows a concentration gradient, but differs from a simple one in that specific carrier molecules are necessarily involved in the passage of a substance through the membrane. These molecules permeate the membrane (may form channels) or at least are associated with it. The substance being transported must contact the carrier. After that, the transporter changes its localization in the membrane or its conformation in such a way that it delivers the substance to the other side of the membrane. If the participation of a carrier is necessary for the transmembrane transition of a substance, then the term "diffusion" is often used instead of the term transport of a substance across a membrane.
With facilitated diffusion (as opposed to simple diffusion), if there is an increase in the gradient of the transmembrane concentration of a substance, then the rate of its passage through the membrane increases only until all membrane carriers are involved. With a further increase in such a gradient, the speed of transport will remain unchanged; it's called saturation phenomenon. Examples of the transport of substances by facilitated diffusion are: the transfer of glucose from the blood to the brain, the reabsorption of amino acids and glucose from primary urine into the blood in the renal tubules.
Exchange diffusion - transport of substances, in which there can be an exchange of molecules of the same substance located on opposite sides of the membrane. The concentration of the substance on each side of the membrane remains unchanged.
A variation of exchange diffusion is the exchange of a molecule of one substance for one or more molecules of another substance. For example, in the smooth muscle fibers of blood vessels and bronchi, one of the ways to remove Ca 2+ ions from the cell is to exchange them for extracellular Na + ions. For three incoming sodium ions, one calcium ion is removed from the cell. An interdependent movement of sodium and calcium through the membrane in opposite directions is created (this type of transport is called antiport). Thus, the cell is freed from excess Ca 2+ , and this is a necessary condition for smooth muscle fiber relaxation. Knowledge of the mechanisms of ion transport through membranes and methods of influencing this transport is an indispensable condition not only for understanding the mechanisms of regulation of vital functions, but also for the correct choice of drugs for the treatment of a large number of diseases (hypertension, bronchial asthma, cardiac arrhythmias, water-salt metabolism disorders). and etc.).
active transport differs from passive in that it goes against the concentration gradients of a substance, using the energy of ATP, which is formed due to cellular metabolism. Thanks to active transport, the forces of not only the concentration but also the electrical gradient can be overcome. For example, with active transport of Na + from the cell, not only the concentration gradient is overcome (outside, the content of Na + is 10-15 times greater), but also the resistance of the electric charge (outside, the cell membrane in the vast majority of cells is positively charged, and this creates a counteraction to the release of positively charged Na + from the cell).
Active transport of Na + is provided by protein Na + , K + dependent ATPase. In biochemistry, the ending "aza" is added to the name of a protein if it has enzymatic properties. Thus, the name Na + , K + -dependent ATPase means that this substance is a protein that cleaves adenosine triphosphoric acid only if there is an obligatory interaction with Na + and K + ions. sodium ions and the transport of two potassium ions into the cell.
There are also proteins that actively transport hydrogen, calcium and chlorine ions. In skeletal muscle fibers, Ca 2+ -dependent ATPase is built into the membranes of the sarcoplasmic reticulum, which forms intracellular containers (cistern, longitudinal tubes) that accumulate Ca 2+. The calcium pump, due to the energy of ATP splitting, transfers Ca 2+ ions from the sarcoplasm to the reticulum cisterns and can create in them a concentration of Ca + approaching 1 (G 3 M, i.e. 10,000 times greater than in the sarcoplasm of the fiber.
secondary active transport characterized by the fact that the transfer of a substance across the membrane is due to the concentration gradient of another substance for which there is an active transport mechanism. Most often, secondary active transport occurs through the use of a sodium gradient, i.e. Na + goes through the membrane towards its lower concentration and pulls another substance with it. In this case, a specific carrier protein built into the membrane is usually used.
For example, the transport of amino acids and glucose from the primary urine into the blood, carried out in the initial section of the renal tubules, occurs due to the fact that the tubular membrane transport protein epithelium binds to the amino acid and sodium ion, and only then changes its position in the membrane in such a way that it transfers the amino acid and sodium to the cytoplasm. For the presence of such transport, it is necessary that the sodium concentration outside the cell be much higher than inside.
To understand the mechanisms of humoral regulation in the body, it is necessary to know not only the structure and permeability of cell membranes for various substances, but also the structure and permeability of more complex formations located between the blood and tissues of various organs.
Physiology of histohematic barriers (HGB). Histo-hematic barriers are a combination of morphological, physiological and physico-chemical mechanisms that function as a whole and regulate the interactions of blood and organs. Histohematic barriers are involved in the creation of homeostasis of the body and individual organs. Due to the presence of HGB, each organ lives in its own special environment, which can differ significantly from blood plasma in terms of the composition of individual ingredients. Particularly powerful barriers exist between the blood and the brain, the blood and tissue of the gonads, the blood and chamber moisture of the eye. Direct contact with the blood has a barrier layer formed by the endothelium of the blood capillaries, followed by the basement membrane with spericytes (middle layer) and then adventitial cells of organs and tissues (outer layer). Histohematic barriers, changing their permeability to various substances, can limit or facilitate their delivery to the organ. For a number of toxic substances, they are impenetrable. This is their protective function.
Blood-brain barrier (BBB) - it is a set of morphological structures, physiological and physicochemical mechanisms that function as a whole and regulate the interaction of blood and brain tissue. The morphological basis of the BBB is the endothelium and the basement membrane of the cerebral capillaries, interstitial elements and glycocalyx, neuroglia, whose peculiar cells (astrocytes) cover the entire surface of the capillary with their legs. The barrier mechanisms also include transport systems of the endothelium of the capillary walls, including pino- and exocytosis, endoplasmic reticulum, channel formation, enzyme systems that modify or destroy incoming substances, as well as proteins that act as carriers. In the structure of brain capillary endothelial membranes, as well as in a number of other organs, aquaporin proteins were found that create channels that selectively let water molecules through.
Brain capillaries differ from capillaries in other organs in that endothelial cells form a continuous wall. At the points of contact, the outer layers of endothelial cells merge, forming the so-called tight junctions.
Among the functions of the BBB are protective and regulatory. It protects the brain from the action of foreign and toxic substances, participates in the transport of substances between the blood and the brain, and thereby creates homeostasis of the intercellular fluid of the brain and cerebrospinal fluid.
The blood-brain barrier is selectively permeable to various substances. Some biologically active substances (for example, catecholamines) practically do not pass through this barrier. The exception is only small areas of the barrier on the border with the pituitary gland, epiphysis and some areas of the hypothalamus, where the permeability of the BBB for all substances is high. In these areas, gaps or channels penetrating the endothelium were found, through which substances from the blood penetrate into the extracellular fluid of the brain tissue or into the neurons themselves.
The high permeability of the BBB in these areas allows biologically active substances to reach those neurons of the hypothalamus and glandular cells, on which the regulatory circuit of the neuroendocrine systems of the body closes.
A characteristic feature of the functioning of the BBB is the regulation of permeability for substances adequately to the prevailing conditions. Regulation is due to: 1) changes in the area of open capillaries, 2) changes in blood flow velocity, 3) changes in the state of cell membranes and intercellular substance, activity of cellular enzyme systems, pinot and exocytosis.
It is believed that the BBB, while creating a significant obstacle to the penetration of substances from the blood into the brain, at the same time well passes these substances in the opposite direction from the brain to the blood.
The permeability of the BBB for various substances varies greatly. Fat-soluble substances, as a rule, penetrate the BBB more easily than water-soluble substances. Oxygen, carbon dioxide, nicotine, ethyl alcohol, heroin, fat-soluble antibiotics (chloramphenicol, etc.) penetrate relatively easily.
Lipid-insoluble glucose and some essential amino acids cannot pass into the brain by simple diffusion. They are recognized and transported by special carriers. The transport system is so specific that it distinguishes stereoisomers of D- and L-glucose. D-glucose is transported, while L-glucose is not. This transport is provided by carrier proteins built into the membrane. Transport is insulin insensitive, but inhibited by cytocholasin B.
Large neutral amino acids (eg, phenylalanine) are transported similarly.
There is also active transport. For example, due to active transport against concentration gradients, Na + K + ions, the amino acid glycine, which acts as an inhibitory mediator, are transported.
The given materials characterize the methods of penetration of biologically important substances through biological barriers. They are essential for understanding the humoral rations in organism.
Control questions and tasks
What are the basic conditions for maintaining the vital activity of an organism?
What is the interaction of the organism with the external environment? Define the concept of adaptation to the environment of existence.
What is the internal environment of the body and its components?
What is homeostasis and homeostatic constants?
Name the limits of fluctuations of rigid and plastic homeostatic constants. Define the concept of their circadian rhythms.
List the most important concepts of the theory of homeostatic regulation.
7 Define irritation and irritants. How are stimuli classified?
What is the difference between the concept of "receptor" from a molecular biological and morphofunctional point of view?
Define the concept of ligands.
What are physiological regulation and closed loop regulation? What are its components?
Name the types and role of feedback.
Give a definition of the concept of the set point of homeostatic regulation.
What are the levels of regulatory systems?
What is the unity and distinctive features of nervous and humoral regulation in the body?
What are the types of humoral regulation? Give them a description.
What is the structure and properties of cell membranes?
17 What are the functions of cell membranes?
What is the diffusion and transport of substances across cell membranes?
Give a description and give examples of active membrane transport.
Define the concept of histohematic barriers.
What is the blood-brain barrier and what is its role? t;
Regulation of the functions of cells, tissues and organs, the relationship between them, i.e. the integrity of the organism, and the unity of the organism and the external environment is carried out by the nervous system and humoral way. In other words, we have two mechanisms of regulation of functions - nervous and humoral.
Nervous regulation is carried out by the nervous system, the brain and spinal cord through the nerves that are supplied to all organs of our body. The body is constantly affected by certain stimuli. The body responds to all these stimuli with a certain activity or, as it is customary to create, the body functions adapt to constantly changing environmental conditions. Thus, a decrease in air temperature is accompanied not only by a narrowing of blood vessels, but also by an increase in metabolism in cells and tissues and, consequently, an increase in heat generation. Due to this, a certain balance is established between heat transfer and heat generation, hypothermia of the body does not occur, and the constancy of body temperature is maintained. Food irritation of the taste buds of the mouth strips causes the separation of saliva and other digestive juices. under the influence of which the digestion of food occurs. Thanks to this, the necessary substances enter the cells and tissues, and a certain balance is established between dissimilation and assimilation. According to this principle, the regulation of other functions of the body occurs.
Nervous regulation is reflex in nature. Various stimuli are perceived by receptors. The resulting excitation from the receptors is transmitted through the sensory nerves to the central nervous system, and from there through the motor nerves to the organs that carry out certain activities. Such responses of the body to stimuli carried out through the central nervous system. called reflexes. The path along which excitation is transmitted during a reflex is called the reflex arc. Reflexes are varied. I.P. Pavlov divided all reflexes into unconditional and conditional. Unconditioned reflexes are congenital reflexes that are inherited. An example of such reflexes are vasomotor reflexes (constriction or expansion of blood vessels in response to skin irritation with cold or heat), salivation reflex (saliva when the taste buds are irritated by food) and many others.
Conditioned reflexes are acquired reflexes, they are developed throughout the life of an animal or person. These reflexes occur
only under certain conditions and can disappear. An example of conditioned reflexes is the separation of saliva at the sight of food, when smelling food, and in a person even when talking about it.
Humoral regulation (Humor - liquid) is carried out through the blood and other liquid and, constituting the internal environment of the body, various chemicals that are produced in the body itself or come from the external environment. Examples of such substances are hormones secreted by the endocrine glands, and vitamins that enter the body with food. Chemicals are carried by the blood throughout the body and affect various functions, in particular the metabolism in cells and tissues. Moreover, each substance affects a certain process that occurs in a particular organ.
Nervous and humoral mechanisms of regulation of functions are interconnected. Thus, the nervous system exerts a regulating influence on the organs not only directly through the nerves, but also through the endocrine glands, changing the intensity of the formation of hormones in these organs and their entry into the blood.
In turn, many hormones and other substances affect the nervous system.
In a living organism, the nervous and humoral regulation of various functions is carried out according to the principle of self-regulation, i.e. automatically. According to this principle of regulation, blood pressure, the constancy of the composition and physico-chemical properties of blood, and body temperature are maintained at a certain level. metabolism, the activity of the heart, respiratory and other organ systems during physical work, etc. change in a strictly coordinated manner.
Due to this, certain relatively constant conditions are maintained in which the activity of the cells and tissues of the body proceeds, or in other words, the constancy of the internal environment is maintained.
It should be noted that in humans, the nervous system plays a leading role in the regulation of the vital activity of the body.
Thus, the human body is a single, integral, complex, self-regulating and self-developing biological system with certain reserve capabilities. Wherein
know that the ability to perform physical work can increase many times, but up to a certain limit. Whereas mental activity actually has no restrictions in its development.
Systematic muscular activity allows, by improving physiological functions, to mobilize the reserves of the body, the existence of which many do not even know. It should be noted that there is a reverse process, a decrease in the functional capabilities of the body and accelerated aging with a decrease in physical activity.
In the course of physical exercises, the higher nervous activity and the functions of the central nervous system are improved. neuromuscular. cardiovascular, respiratory, excretory and other systems, metabolism and energy, as well as the system of their neurohumoral regulation.
The human body, using the properties of self-regulation of internal processes under external influence, realizes the most important property - adaptation to changing external conditions, which is a determining factor in the ability to develop physical qualities and motor skills during training.
Let us consider in more detail the nature of physiological changes in the process of training.
Physical activity leads to diverse changes in metabolism, the nature of which depends on the duration, power of work and the number of muscles involved. During physical activity, catabolic processes, mobilization and use of energy substrates predominate, and intermediate metabolic products accumulate. The rest period is characterized by the predominance of anabolic processes, the accumulation of a reserve of nutrients, and increased protein synthesis.
The recovery rate depends on the magnitude of the changes that occur during operation, that is, on the magnitude of the load.
During the rest period, the metabolic changes that occurred during muscle activity are eliminated. If during physical activity catabolic processes, mobilization and use of energy substrates predominate, there is an accumulation of intermediate metabolic products, then the rest period is characterized by the predominance of anabolic processes, the accumulation of a reserve of nutrients, and increased protein synthesis.
In the post-working period, the intensity of aerobic oxidation increases, oxygen consumption is increased, i.e. oxygen debt is eliminated. The substrate for oxidation is the intermediate metabolic products formed during muscle activity, lactic acid, ketone bodies, keto acids. Carbohydrate reserves during physical work, as a rule, are significantly reduced, so fatty acids become the main substrate for oxidation. Due to the increased use of lipids during the recovery period, the respiratory quotient decreases.
The recovery period is characterized by increased protein biosynthesis, which is inhibited during physical work, and the formation and excretion of the end products of protein metabolism (urea, etc.) from the body also increases.
The recovery rate depends on the magnitude of the changes that occur during operation, i.e. on the magnitude of the load, which is schematically shown in Fig. one
Fig.1 Scheme of the processes of expenditure and recovery of sources
energy during muscular activity of military intensity
Restoration of changes that occur under the influence of loads of low and medium intensity is slower than after loads of increased and maximum intensity, which is explained by deeper changes during the period of work. After increased intensity loads, the observed metabolic rate, substances not only reaches the initial level, but also exceeds it. This increase above the initial level is called over recovery (super compensation). It is registered only when the load exceeds a certain level in value, i.e. when the resulting changes in metabolism affect the genetic apparatus of the cell. The severity of over-recovery and its duration are directly dependent on the intensity of the load.
The phenomenon of overpowering is an important mechanism of adaptation (of an organ) to changing conditions of functioning and is important for understanding the biochemical foundations of sports training. It should be noted that as a general biological pattern, it extends not only to the accumulation of energy material, but also to the synthesis of proteins, which, in particular, manifests itself in the form of working hypertrophy of skeletal muscles, the heart muscle. After an intense load, the synthesis of a number of enzymes increases (enzyme induction), the concentration of creatine phosphate and myoglobin increases, and a number of other changes occur.
It has been established that active muscular activity causes an increase in the activity of the cardiovascular, respiratory and other body systems. In any human activity, all organs and systems of the body act in concert, in close unity. This relationship is carried out with the help of the nervous system and humoral (fluid) regulation.
The nervous system regulates the activity of the body through bioelectric impulses. The main nervous processes are excitation and inhibition that occur in nerve cells. Excitation- the active state of nerve cells, when they transmit silt, they themselves direct nerve impulses to other cells: nerve, muscle, glandular and others. Braking- the state of nerve cells, when their activity is aimed at recovery. Sleep, for example, is a state of the nervous system, when the vast majority of nerve cells of the central nervous system are inhibited.
Humoral regulation is carried out through the blood by means of special chemicals (hormones) secreted by the endocrine glands, the concentration ratio CO2 and O2 through other mechanisms. For example, in the pre-launch state, when intense physical activity is expected, the endocrine glands (adrenal glands) secrete a special hormone, adrenaline, into the blood, which enhances the activity of the cardiovascular system.
Humoral and nervous regulation are carried out in unity. The leading role is assigned to the central nervous system, the brain, which is, as it were, the central headquarters for controlling the vital activity of the organism.
The complex structure of the human body is currently the pinnacle of evolutionary transformation. Such a system needs special ways of coordinating. Humoral regulation is carried out with the help of hormones. But the nervous one is the coordination of activity with the help of the organ system of the same name.
What is the regulation of body functions
The human body has a very complex structure. From cells to organ systems, it is an interconnected system, for the normal functioning of which a clear regulatory mechanism must be created. It is carried out in two ways. The first way is the fastest. It's called neural regulation. This process is implemented by the system of the same name. There is an erroneous opinion that humoral regulation is carried out with the help of nerve impulses. However, this is not at all the case. Humoral regulation is carried out with the help of hormones that enter the fluid environment of the body.
Features of nervous regulation
This system includes the central and peripheral department. If the humoral regulation of body functions is carried out with the help of chemicals, then this method is a "traffic highway", linking the body into a single whole. This process happens quite quickly. Just imagine that you touched a hot iron with your hand or went barefoot in the snow in winter. The reaction of the body will be almost instantaneous. It has the most important protective value, promotes both adaptation and survival in various conditions. The nervous system underlies the innate and acquired reactions of the body. The first are unconditioned reflexes. These include respiratory, sucking, blinking. And over time, a person develops acquired reactions. These are unconditioned reflexes.
Features of humoral regulation
Humoral is carried out with the help of specialized organs. They are called glands and are combined into a separate system called the endocrine system. These organs are formed by a special type of epithelial tissue and are capable of regeneration. The action of hormones is long-term and continues throughout a person's life.
What are hormones
The glands secrete hormones. Due to their special structure, these substances accelerate or normalize various physiological processes in the body. For example, at the base of the brain is the pituitary gland. It produces as a result of which the human body increases in size for more than twenty years.
Glands: features of the structure and functioning
So, humoral regulation in the body is carried out with the help of special organs - glands. They ensure the constancy of the internal environment, or homeostasis. Their action is in the nature of feedback. For example, such an important indicator for the body as the level of sugar in the blood is regulated by the hormone insulin in the upper limit and glucagon in the lower. This is the mechanism of action of the endocrine system.
Exocrine glands
Humoral regulation is carried out with the help of glands. However, depending on the structural features, these organs are combined into three groups: external (exocrine), internal (endocrine) and mixed secretion. Examples of the first group are salivary, sebaceous and lacrimal. They are characterized by the presence of their own excretory ducts. Exocrine glands secrete on the surface of the skin or in body cavities.
Endocrine glands
Endocrine glands secrete hormones into the blood. They do not have their own excretory ducts, so humoral regulation is carried out with the help of body fluids. Getting into the blood or lymph, they are carried throughout the body, come to each of its cells. And the result of this is the acceleration or deceleration of various processes. This may be growth, sexual and psychological development, metabolism, the activity of individual organs and their systems.
Hypo- and hyperfunctions of the endocrine glands
The activity of each endocrine gland has "two sides of the coin." Let's look at this with specific examples. If the pituitary gland secretes an excess amount of growth hormone, gigantism develops, and with a lack of this substance, dwarfism is observed. Both are deviations from normal development.
The thyroid gland secretes several hormones at once. These are thyroxine, calcitonin and triiodothyronine. With their insufficient number, infants develop cretinism, which manifests itself in mental retardation. If hypofunction manifests itself in adulthood, it is accompanied by swelling of the mucous membrane and subcutaneous tissue, hair loss and drowsiness. If the amount of hormones of this gland exceeds the normal limit, a person may develop Graves' disease. It manifests itself in increased excitability of the nervous system, trembling of the limbs, causeless anxiety. All this inevitably leads to emaciation and loss of vitality.
The endocrine glands also include the parathyroid, thymus, and adrenal glands. The last glands at the time of a stressful situation secrete the hormone adrenaline. Its presence in the blood ensures the mobilization of all vital forces and the ability to adapt and survive in non-standard conditions for the body. First of all, this is expressed in providing the muscular system with the necessary amount of energy. The reverse-acting hormone, which is also secreted by the adrenal glands, is called norepinephrine. It is also of great importance for the body, since it protects it from excessive excitability, loss of strength, energy, and rapid wear. This is another example of the reverse action of the human endocrine system.
Glands of mixed secretion
These include the pancreas and gonads. The principle of their work is twofold. just two types and glucagon. They, respectively, lower and increase the level of glucose in the blood. In a healthy human body, this regulation goes unnoticed. However, if this function is violated, a serious disease occurs, which is called diabetes mellitus. People with this diagnosis need artificial insulin administration. As an external secretion gland, the pancreas secretes digestive juice. This substance is secreted into the first section of the small intestine - the duodenum. Under its influence, there is a process of splitting complex biopolymers to simple ones. It is in this section that proteins and lipids break down into their constituent parts.
The gonads also secrete various hormones. These are male testosterone and female estrogen. These substances begin to act even in the course of embryonic development, sex hormones affect the formation of sex, and then form certain sexual characteristics. Like exocrine glands, they form gametes. Man, like all mammals, is a dioecious organism. Its reproductive system has a general structural plan and is represented by the gonads, their ducts and cells directly. In women, these are paired ovaries with their tracts and eggs. In men, the reproductive system consists of testes, excretory canals and sperm cells. In this case, these glands act as glands of external secretion.
Nervous and humoral regulation are closely interrelated. They work as a single mechanism. Humoral is more ancient in origin, has a long-term effect and acts on the entire body, since hormones are carried by the blood and enter every cell. And the nervous one works pointwise, at a specific time and in a specific place, according to the "here and now" principle. After changing the conditions, its action is terminated.
So, the humoral regulation of physiological processes is carried out with the help of the endocrine system. These organs are able to secrete special biologically active substances into liquid media, which are called hormones.
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