The practical significance of the discovery of homeostasis. The concept of homeostasis
In his book The Wisdom of the Body, he proposed the term as a name for "the coordinated physiological processes that maintain the body's most stable states." In the future, this term was extended to the ability to dynamically maintain the constancy of its internal state of any open system. However, the concept of the constancy of the internal environment was formulated as early as 1878 by the French scientist Claude Bernard.
General information
The term "homeostasis" is most commonly used in biology. For multicellular organisms to exist, it is necessary to maintain the constancy of the internal environment. Many ecologists are convinced that this principle also applies to the external environment. If the system is unable to restore its balance, it may eventually cease to function.
Complex systems - for example, the human body - must have homeostasis in order to maintain stability and exist. These systems not only have to strive to survive, they also have to adapt to environmental changes and evolve.
properties of homeostasis
Homeostatic systems have the following properties:
- instability system: tests how it can best adapt.
- Striving for balance: all the internal, structural and functional organization of systems contributes to maintaining balance.
- unpredictability: The resultant effect of a certain action can often be different from what was expected.
- Regulation of the amount of micronutrients and water in the body - osmoregulation. Carried out in the kidneys.
- Removal of waste products of the metabolic process - isolation. It is carried out by exocrine organs - kidneys, lungs, sweat glands and gastrointestinal tract.
- Body temperature regulation. Lowering the temperature through sweating, a variety of thermoregulatory reactions.
- Regulation of blood glucose levels. Mainly carried out by the liver, insulin and glucagon secreted by the pancreas.
It is important to note that although the body is in balance, its physiological state can be dynamic. Many organisms exhibit endogenous changes in the form of circadian, ultradian, and infradian rhythms. So, even while in homeostasis, body temperature, blood pressure, heart rate and most metabolic indicators are not always at a constant level, but change over time.
Mechanisms of homeostasis: feedback
When there is a change in variables, there are two main types of feedback that the system responds to:
- Negative feedback, expressed as a reaction in which the system responds in such a way as to reverse the direction of change. Since the feedback serves to maintain the constancy of the system, it allows you to maintain homeostasis.
- For example, when the concentration of carbon dioxide in the human body increases, the lungs are signaled to increase their activity and exhale more carbon dioxide.
- Thermoregulation is another example of negative feedback. When body temperature rises (or falls), thermoreceptors in the skin and hypothalamus register the change, triggering a signal from the brain. This signal, in turn, causes a response - a decrease in temperature (or increase).
- Positive feedback, which is expressed as an amplification of the change in a variable. It has a destabilizing effect, so it does not lead to homeostasis. Positive feedback is less common in natural systems, but also has its uses.
- For example, in nerves, a threshold electrical potential causes the generation of a much larger action potential. Blood clotting and birth events are other examples of positive feedback.
Stable systems need combinations of both types of feedback. While negative feedback allows you to return to a homeostatic state, positive feedback is used to move to a completely new (and quite possibly less desirable) state of homeostasis, a situation called "metastability". Such catastrophic changes can occur, for example, with an increase in nutrients in rivers with clear water, which leads to a homeostatic state of high eutrophication (algae overgrowth of the channel) and turbidity.
Ecological homeostasis
In disturbed ecosystems, or subclimax biological communities - like, for example, the island of Krakatoa, after a strong volcanic eruption in - the state of homeostasis of the previous forest climax ecosystem was destroyed, like all life on this island. Krakatoa has gone through a chain of ecological changes in the years since the eruption, in which new plant and animal species replaced each other, which led to biodiversity and, as a result, a climax community. Ecological succession in Krakatoa took place in several stages. A complete chain of successions leading to a climax is called a preserie. In the example of Krakatau, this island developed a climax community with eight thousand different species recorded in , a hundred years after the eruption destroyed life on it. The data confirm that the position is maintained in homeostasis for some time, while the emergence of new species very quickly leads to the rapid disappearance of old ones.
The case of Krakatoa and other disturbed or intact ecosystems shows that the initial colonization by pioneer species occurs through positive feedback reproduction strategies in which the species disperse, producing as many offspring as possible, but with little or no investment in the success of each individual. . In such species, there is a rapid development and an equally rapid collapse (for example, through an epidemic). As an ecosystem approaches climax, such species are replaced by more complex climax species that adapt through negative feedback to the specific conditions of their environment. These species are carefully controlled by the potential capacity of the ecosystem and follow a different strategy - producing smaller offspring, in the reproductive success of which in the conditions of the microenvironment of its specific ecological niche, more energy is invested.
Development begins with the pioneer community and ends with the climax community. This climax community is formed when flora and fauna come into balance with the local environment.
Such ecosystems form heterarchies, in which homeostasis at one level contributes to homeostatic processes at another complex level. For example, the loss of leaves on a mature tropical tree makes room for new growth and enriches the soil. Equally, the tropical tree reduces the access of light to lower levels and helps prevent other species from invading. But trees also fall to the ground and the development of the forest depends on the constant change of trees, the cycle of nutrients carried out by bacteria, insects, fungi. Similarly, such forests contribute to ecological processes, such as the regulation of microclimates or ecosystem hydrological cycles, and several different ecosystems may interact to maintain river drainage homeostasis within a biological region. The variability of bioregions also plays a role in the homeostatic stability of a biological region, or biome.
Biological homeostasis
Homeostasis acts as a fundamental characteristic of living organisms and is understood as maintaining the internal environment within acceptable limits.
The internal environment of the body includes body fluids - blood plasma, lymph, intercellular substance and cerebrospinal fluid. Maintaining the stability of these fluids is vital for organisms, while its absence leads to damage to the genetic material.
Homeostasis in the human body
Various factors affect the ability of body fluids to support life. Among them are parameters such as temperature, salinity, acidity and the concentration of nutrients - glucose, various ions, oxygen, and waste products - carbon dioxide and urine. Since these parameters affect the chemical reactions that keep the organism alive, there are built-in physiological mechanisms to keep them at the required level.
Homeostasis cannot be considered the cause of the processes of these unconscious adaptations. It should be taken as a general characteristic of many normal processes acting together, and not as their root cause. Moreover, there are many biological phenomena that do not fit this model - for example, anabolism.
Other areas
The concept of "homeostasis" is also used in other areas.
The actuary can talk about risk homeostasis, in which, for example, people who have non-stick brakes on their cars are not in a safer position than those who do not, because these people unconsciously compensate for a safer car by risky driving. This happens because some of the holding mechanisms - such as fear - stop working.
Sociologists and psychologists can talk about stress homeostasis- the desire of a population or individual to remain at a certain stress level, often artificially causing stress if the "natural" level of stress is not enough.
Examples
- thermoregulation
- Skeletal muscle trembling may begin if the body temperature is too low.
- Another type of thermogenesis involves the breakdown of fats to release heat.
- Sweating cools the body through evaporation.
- Chemical regulation
- The pancreas secretes insulin and glucagon to control blood glucose levels.
- The lungs take in oxygen and release carbon dioxide.
- The kidneys excrete urine and regulate the level of water and a number of ions in the body.
Many of these organs are controlled by hormones from the hypothalamic-pituitary system.
see also
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Synonyms:See what "Homeostasis" is in other dictionaries:
Homeostasis... Spelling Dictionary
homeostasis- The general principle of self-regulation of living organisms. Perls strongly emphasizes the importance of this concept in his work The Gestalt Approach and Eye Witness to Therapy. Brief explanatory psychological and psychiatric dictionary. Ed. igisheva. 2008 ... Great Psychological Encyclopedia
Homeostasis (from the Greek. similar, identical and state), the property of the body to maintain its parameters and physiological. functions in def. range, based on the stability of the internal. body environment in relation to perturbing influences ... Philosophical Encyclopedia
- (from the Greek homoios the same, similar and Greek stasis immobility, standing), homeostasis, the ability of an organism or system of organisms to maintain a stable (dynamic) balance in changing environmental conditions. Homeostasis in a population Ecological dictionary
Homeostasis (from homeo... and Greek stasis immobility, state), the ability of biol. systems to resist change and remain dynamic. refers to the constancy of the composition and properties. The term "G." proposed by W. Kennon in 1929 to characterize states ... Biological encyclopedic dictionary
Homeostasis is a self-regulating process in which all biological systems strive to maintain stability during the period of adaptation to certain conditions that are optimal for survival. Any system, being in dynamic equilibrium, strives to achieve a stable state that resists external factors and stimuli.
The concept of homeostasis
All body systems must work together to maintain proper homeostasis within the body. Homeostasis is the regulation of body temperature, water content, and carbon dioxide levels. For example, diabetes mellitus is a condition in which the body cannot regulate blood glucose levels.
Homeostasis is a term that is used both to describe the existence of organisms in an ecosystem and to describe the successful functioning of cells within an organism. Organisms and populations can maintain homeostasis while maintaining stable birth and death rates.
Feedback
Feedback is a process that occurs when the body's systems need to be slowed down or completely stopped. When a person eats, food enters the stomach and digestion begins. In between meals, the stomach should not work. The digestive system works with a series of hormones and nerve impulses to stop and start acid production in the stomach.
Another example of negative feedback can be observed in the case of an increase in body temperature. The regulation of homeostasis is manifested by sweating, a protective reaction of the body to overheating. In this way, the rise in temperature is stopped and the problem of overheating is neutralized. In case of hypothermia, the body also provides for a number of measures taken in order to warm up.
Maintaining internal balance
Homeostasis can be defined as a property of an organism or system that helps it to maintain given parameters within the normal range of values. This is the key to life, and the wrong balance in maintaining homeostasis can lead to diseases such as hypertension and diabetes.
Homeostasis is a key element in understanding how the human body works. Such a formal definition characterizes a system that regulates its internal environment and seeks to maintain the stability and regularity of all processes occurring in the body.
Homeostatic regulation: body temperature
Body temperature control in humans is a good example of homeostasis in a biological system. When a person is healthy, their body temperature fluctuates around + 37°C, but various factors can affect this value, including hormones, metabolic rate, and various diseases that cause fever.
In the body, temperature regulation is controlled in a part of the brain called the hypothalamus. Through the bloodstream to the brain, temperature signals are received, as well as the analysis of the results of data on the frequency of respiration, blood sugar and metabolism. The loss of heat in the human body also contributes to reduced activity.
Water-salt balance
No matter how much water a person drinks, the body does not swell like a balloon, and the human body does not shrink like raisins if you drink very little. Probably, someone once thought about it at least once. One way or another, the body knows how much fluid needs to be stored to maintain the desired level.
The concentration of salt and glucose (sugar) in the body is maintained at a constant level (in the absence of negative factors), the amount of blood in the body is about 5 liters.
Blood sugar regulation
Glucose is a type of sugar found in the blood. The human body must maintain proper glucose levels in order for a person to remain healthy. When glucose levels get too high, the pancreas releases the hormone insulin.
If the blood glucose level drops too low, the liver converts the glycogen in the blood, thereby raising the sugar level. When pathogenic bacteria or viruses enter the body, it begins to fight the infection before the pathogenic elements can lead to any health problems.
Pressure under control
Maintaining healthy blood pressure is also an example of homeostasis. The heart can sense changes in blood pressure and send signals to the brain for processing. Next, the brain sends a signal back to the heart with instructions on how to respond correctly. If the blood pressure is too high, it must be lowered.
How is homeostasis achieved?
How does the human body regulate all systems and organs and compensate for the ongoing changes in the environment? This is due to the presence of many natural sensors that control temperature, blood salt composition, blood pressure and many other parameters. These detectors send signals to the brain, to the main control center, in case some values deviate from the norm. After that, compensatory measures are launched to restore the normal state.
Maintaining homeostasis is incredibly important for the body. The human body contains a certain amount of chemicals known as acids and bases, and their proper balance is essential for the optimal functioning of all organs and body systems. The level of calcium in the blood must be maintained at the proper level. Because breathing is involuntary, the nervous system provides the body with much-needed oxygen. When toxins enter your bloodstream, they disrupt the body's homeostasis. The human body responds to this disturbance with the help of the urinary system.
It is important to emphasize that the body's homeostasis works automatically if the system functions normally. For example, a reaction to heat - the skin turns red, because its small blood vessels automatically dilate. Trembling is a response to being cold. Thus, homeostasis is not a set of organs, but the synthesis and balance of bodily functions. Together, this allows you to maintain the entire body in a stable state.
Homeostasis - maintenance of the body's internal environment
The world around us is constantly changing. Winter winds force us to put on warm clothes and gloves, while central heating encourages us to take them off. The summer sun reduces the need for heat retention, at least until efficient air conditioning does the opposite. And yet, regardless of the ambient temperature, the individual body temperature of healthy people you know is unlikely to differ by much more than one tenth of a degree. In humans and other warm-blooded animals, the temperature of the internal regions of the body is kept at a constant level somewhere around 37 ° C, although it may rise and fall somewhat in connection with the daily rhythm.
Most people eat differently. Some prefer a good breakfast, a light lunch and a hearty lunch with the obligatory dessert. Others don't eat most of the day, but at noon they like to have a good snack and a little nap. Some only do what they chew, others seem not to care about food at all. And yet, if you measure the blood sugar content of the students in your class, then it will all be close to 0.001 g (1 mg) per milliliter of blood, despite the large difference in the diet and distribution of meals.
Precise regulation of body temperature and blood glucose are just two examples of the most important functions under the control of the nervous system. The composition of the fluids that surround all our cells is continuously regulated, which allows for its amazing constancy.
Maintaining a constant internal environment is called homeostasis (homeo - the same, similar; stasis - stability, balance). The main responsibility for homeostatic regulation is borne by the autonomic (autonomous) and intestinal sections of the peripheral nervous system, as well as the central nervous system, which gives orders to the body through the pituitary gland and other endocrine organs. Working together, these systems coordinate the needs of the body with environmental conditions. (If this statement sounds familiar to you, remember that we used exactly the same words to describe the main function of the brain.)
The French physiologist Claude Bernard, who lived in the 19th century and devoted himself entirely to the study of the processes of digestion and the regulation of blood flow, considered body fluids as an “internal environment” ( milieu interne). In different organisms, the concentration of certain salts and the normal temperature may be somewhat different, but within a species, the internal environment of individuals corresponds to the standards characteristic of this species. Only short-term and not very large deviations from these standards are allowed, otherwise the organism cannot remain healthy and contribute to the survival of the species. Walter B. Cannon, the foremost American physiologist of the middle of this century, extended Bernard's concept of the internal environment. He believed that the independence of the individual from continuous changes in external conditions is ensured by the work homeostatic mechanisms that maintain the constancy of the internal environment.
The ability of an organism to cope with the demands of its environment varies greatly from species to species. A person who uses complex types of behavior in addition to the internal mechanisms of homeostasis, apparently, has the greatest independence from external conditions. Nevertheless, many animals surpass it in certain species-specific capabilities. For example, polar bears are more resistant to cold; some species of spiders and lizards living in deserts tolerate heat better; camels can go longer without water. In this chapter, we will consider a number of structures that allow us to gain some degree of independence from the changing physical conditions of the external world. We will also take a closer look at the regulatory mechanisms that maintain the constancy of our internal environment.
Astronauts wear special suits (suits) that allow them to maintain normal body temperature, sufficient oxygen tension in the blood and blood pressure when working in an environment close to vacuum. Special sensors built into these suits record oxygen concentration, body temperature, and heart rate indicators and report these data to the spacecraft computers, which, in turn, to ground control computers. The computers of a controlled spacecraft can cope with almost any of the predictable situations regarding the needs of the organism. If any unforeseen problem arises, computers located on Earth are connected to solve it, which send new commands directly to the suit's instruments.
In the body, registration of sensory data and local control is carried out by the autonomic nervous system with the participation of the endocrine system, which assumes the function of general coordination.
autonomic nervous system
Some general principles of organization of sensory and motor systems will be very useful to us in the study of systems of internal regulation. All three divisions autonomic (autonomous) nervous system have " sensory" and " motor" Components. While the former register indicators of the internal environment, the latter enhance or inhibit the activity of those structures that carry out the process of regulation itself.
Intramuscular receptors, along with receptors located in tendons and some other places, respond to pressure and stretch. Together, they make up a special kind of internal sensory system that helps control our movements.
The receptors involved in homeostasis act in a different way: they sense changes in blood chemistry or pressure fluctuations in the vascular system and in hollow internal organs such as the digestive tract and bladder. These sensory systems, which collect information about the internal environment, are very similar in their organization to systems that receive signals from the surface of the body. Their receptor neurons form the first synaptic switches inside the spinal cord. Along the motor pathways of the autonomic system go commands to the bodies directly regulating the internal environment. These paths begin with special autonomic preganglionic neurons
spinal cord. Such an organization is somewhat reminiscent of the organization of the spinal level of the motor system.
The focus of this chapter will be on those motor components of the autonomic system that innervate the muscles of the heart, blood vessels, and intestines, causing them to contract or relax. The same fibers also innervate the glands, causing the process of secretion.
autonomic nervous system consists of two large sections sympathetic and parasympathetic. Both divisions have one structural feature that we have not encountered before: the neurons that control the muscles of the internal organs and glands lie outside the central nervous system, forming small encapsulated clusters of cells called ganglia. Thus, in the autonomic nervous system there is an additional link between the spinal cord and the terminal working organ (effector).
Autonomic neurons of the spinal cord combine sensory information from internal organs and other sources. On this basis, they then regulate the activity autonomic ganglion neurons. The connections between the ganglia and the spinal cord are called preganglionic fibers . The neurotransmitter used to transmit impulses from the spinal cord to ganglion neurons in both the sympathetic and parasympathetic regions is almost always acetylcholine, the same neurotransmitter by which the motor neurons of the spinal cord directly control the skeletal muscles. As in the fibers that innervate skeletal muscles, the action of acetylcholine can be enhanced in the presence of nicotine and blocked by curare. Axons going from autonomic ganglion neurons, or postganglionic fibers , then go to the target organs, forming many branches there.
The sympathetic and parasympathetic divisions of the autonomic nervous system are different
1) according to the levels at which preganglionic fibers exit the spinal cord;
2) by the proximity of the location of the ganglia to the target organs;
3) by the neurotransmitter that postganglionic neurons use to regulate the functions of these target organs.
We will now consider these features.
Sympathetic nervous system
In the sympathetic system, preganglionic fibers exit from the thoracic and lumbar spinal cord. Its ganglia are located quite close to the spinal cord, and very long postganglionic fibers run from them to the target organs (see Fig. 63). The main mediator of the sympathetic nerves is norepinephrine, one of the catecholamines, which also serves as a mediator in the central nervous system.
Rice. 63. The sympathetic and parasympathetic divisions of the autonomic nervous system, the organs they innervate, and their effect on each organ.
To understand which organs are affected by the sympathetic nervous system, it is easiest to imagine what happens to an excited animal, ready for a fight or flight response.
The pupils dilate to let in more light; the frequency of heart contractions increases, and each contraction becomes more powerful, which leads to an increase in overall blood flow. Blood drains from the skin and internal organs to the muscles and brain. Motility of the gastrointestinal system weakens, digestion processes slow down. Muscles along the airways leading to the lungs relax, allowing for faster breathing and increased gas exchange. The cells of the liver and adipose tissue give more glucose and fatty acids into the blood - high-energy fuel, and the pancreas is instructed to produce less insulin. This allows the brain to receive a greater proportion of the glucose circulating in the bloodstream, since unlike other organs, the brain does not require insulin to utilize blood sugar. The mediator of the sympathetic nervous system, which carries out all these changes, is norepinephrine.
There is an additional system that has an even more generalized effect in order to better ensure all these changes. They sit on the tops of the kidneys like two small caps, adrenal glands . In their inner part - the medulla - there are special cells innervated by preganglionic sympathetic fibers. These cells in the process of embryonic development are formed from the same neural crest cells from which the sympathetic ganglia are formed. Thus, the medulla is a component of the sympathetic nervous system. When activated by preganglionic fibers, medulla cells release their own catecholamines (norepinephrine and epinephrine) directly into the blood for delivery to target organs (Fig. 64). Circulating hormone mediators - serve as an example of how the regulation of endocrine organs is carried out (see p. 89).
parasympathetic nervous system
In the parasympathetic preganglionic fibers go from the brain stem("cranial component") and from the lower, sacral segments of the spinal cord(see Fig. 63 above). They form, in particular, a very important nerve trunk called vagus nerve , whose numerous branches carry out all the parasympathetic innervation of the heart, lungs and intestinal tract. (The vagus nerve also transmits sensory information from these organs back to the central nervous system.) Preganglionic parasympathetic axons very long, because ganglia are usually located near or within the tissues they innervate.
At the ends of the fibers of the parasympathetic system, a neurotransmitter is used acetylcholine. The response of the respective target cells to acetylcholine is insensitive to the action of nicotine or curare. Instead, acetylcholine receptors are activated by muscarine and blocked by atropine.
The predominance of parasympathetic activity creates conditions for " rest and recovery» organism. At its extreme, the general pattern of parasympathetic activation is reminiscent of the resting state that comes after a hearty meal. Increased blood flow to the digestive tract accelerates the movement of food through the intestines and enhances the secretion of digestive enzymes. The frequency and strength of heart contractions decrease, the pupils constrict, the lumen of the airways decreases, and the formation of mucus in them increases. The bladder contracts. Taken together, these changes return the body to that peaceful state that preceded the "fight or flight" response. (All of this is illustrated in Figure 63; see also Chapter 6.)
Comparative characteristics of the departments of the autonomic nervous system
The sympathetic system, with its extremely long postganglionic fibers, is very different from the parasympathetic system, in which, on the contrary, the preganglionic fibers are longer and the ganglia are located near or inside the target organs. Many internal organs, such as the lungs, heart, salivary glands, bladder, gonads, receive innervation from both parts of the autonomic system (they are said to have " double innervation"). Other tissues and organs, such as muscle arteries, receive only sympathetic innervation. On the whole, it can be said that two departments work alternately: depending on the activity of the organism and on the commands of the higher vegetative centers, one or the other of them dominates.
This characterization, however, is not entirely correct. Both systems are constantly in a state of varying degrees of activity.. The fact that target organs such as the heart or the iris can respond to impulses from both areas simply reflects their complementary role. For example, when you are very angry, your blood pressure rises, which excites the corresponding receptors located in the carotid arteries. These signals are received by the integrating center of the cardiovascular system, located in the lower part of the brainstem and known as the nuclei of the solitary tract. Excitation of this center activates the preganglionic parasympathetic fibers of the vagus nerve, which leads to a decrease in the frequency and strength of heart contractions. At the same time, under the influence of the same coordinating vascular center, sympathetic activity is inhibited, counteracting an increase in blood pressure.
How essential is the functioning of each of the departments for adaptive reactions? Surprisingly, not only animals, but also people can endure almost complete shutdown of the sympathetic nervous system with no visible ill effects. This shutdown is recommended for some forms of persistent hypertension.
And here it's not so easy to do without the parasympathetic nervous system. People who have undergone such an operation and found themselves outside the protective conditions of a hospital or laboratory adapt very poorly to the environment. They cannot regulate body temperature when exposed to heat or cold; with blood loss, their blood pressure regulation is disturbed, and with any intense muscle load, fatigue quickly develops.
Diffuse intestinal nervous system
Recent studies have revealed the existence third important division of the autonomic nervous system - diffuse intestinal nervous system . This department is responsible for the innervation and coordination of the digestive organs. Its work is independent of the sympathetic and parasympathetic systems, but can be modified under their influence. This is an additional link that connects the autonomic postganglionic nerves with the glands and muscles of the gastrointestinal tract.
The ganglia of this system innervate the walls of the intestines. Axons from the cells of these ganglia cause contractions of the annular and longitudinal muscles, pushing food through the gastrointestinal tract, a process called peristalsis. Thus, these ganglia determine the features of local peristaltic movements. When the food mass is inside the intestine, it slightly stretches its walls, which causes a narrowing of the area located slightly higher along the course of the intestine, and relaxation of the area located slightly below. As a result, the food mass is pushed further. However, under the influence of parasympathetic or sympathetic nerves, the activity of the intestinal ganglia can change. Activation of the parasympathetic system enhances peristalsis, and activation of the sympathetic system weakens it.
Acetylcholine serves as a mediator that excites the smooth muscles of the intestine. However, inhibitory signals leading to relaxation appear to be transmitted by various substances, of which only a few have been studied. Among the gut neurotransmitters, there are at least three that also act in the central nervous system: somatostatin (see below), endorphins, and substance P (see Chapter 6).
Central regulation of the functions of the autonomic nervous system
The central nervous system exercises control over the autonomic system to a much lesser extent than over the sensory or skeletal motor system. Areas of the brain that are most associated with autonomic functions are hypothalamus and brain stem, especially that part of it that is located directly above the spinal cord - the medulla oblongata. It is from these areas that the main pathways go to sympathetic and parasympathetic preganglionic autonomic neurons at the spinal level.
Hypothalamus. The hypothalamus is one of the areas of the brain, the general structure and organization of which is more or less similar in representatives of various classes of vertebrates.
In general, it is considered that hypothalamus is the focus of visceral integrative functions. Signals from the neuronal systems of the hypothalamus directly enter the networks that excite the preganglionic sections of the autonomic nerve pathways. In addition, this region of the brain exercises direct control over the entire endocrine system through specific neurons that regulate the secretion of hormones from the anterior pituitary gland, and the axons of other hypothalamic neurons terminate in the posterior pituitary gland. Here, these endings secrete mediators that circulate in the blood as hormones: 1) vasopressin, which increases blood pressure in emergency cases, when there is a loss of fluid or blood; it also reduces the excretion of water in the urine (which is why vasopressin is also called antidiuretic hormone); 2) oxytocin, stimulating uterine contractions at the final stage of childbirth.
Rice. 65. Hypothalamus and pituitary gland. Schematically shows the main functional areas of the hypothalamus.
Although among the clusters of hypothalamic neurons there are several clearly demarcated nuclei, most of the hypothalamus is a collection of zones with blurred boundaries (Fig. 65). However, there are quite pronounced nuclei in three zones. We will now consider the functions of these structures.
1. Periventricular zone directly adjacent to the third cerebral ventricle, which passes through the center of the hypothalamus. Cells lining the ventricle relay information to neurons in the periventricular zone about important internal parameters that may need to be regulated, such as temperature, salt concentration, and levels of hormones secreted by the thyroid, adrenals, or gonads, as instructed by the pituitary gland.
2. Medial zone contains most of the pathways by which the hypothalamus exercises endocrine control through the pituitary gland. It can be said very approximately that the cells of the periventricular zone control the actual execution of commands given to the pituitary gland by the cells of the medial zone.
3. Through lateral zone cells control over the hypothalamus from the higher instances of the cerebral cortex and the limbic system. It also receives sensory information from the centers of the medulla oblongata, which coordinate respiratory and cardiovascular activity. The lateral zone is where higher brain centers can make adjustments to the reactions of the hypothalamus to changes in the internal environment. In the cortex, for example, comparison of information coming from two sources - internal and external environment. If, say, the cortex decides that the time and circumstances are not suitable for eating, the sensory reports of low blood sugar and an empty stomach will be put aside until a more favorable moment. Ignoring the hypothalamus by the limbic system is less likely. Rather, this system can add emotional and motivational coloring to the interpretation of external sensory cues, or compare perceptions of the environment based on these cues with similar situations in the past.
Together with the cortical and limbic components, the hypothalamus also performs many routine integrating actions, and over much longer periods of time than during the implementation of short-term regulatory functions. The hypothalamus “knows” in advance what needs the body will have in a normal daily rhythm of life. He, for example, brings the endocrine system into full readiness for action as soon as we wake up. It also monitors the hormonal activity of the ovaries throughout the menstrual cycle; takes steps to prepare the uterus for the arrival of a fertilized egg. In migratory birds and hibernating mammals, the hypothalamus, with its ability to determine the length of daylight hours, coordinates the life of the organism during cycles lasting several months. (These aspects of centralized regulation of internal functions will be discussed in Chapters 5 and 6.)
Medulla(thalamus and hypothalamus)
The hypothalamus makes up less than 5% of the entire brain mass. However, this small amount of tissue contains centers that support all the functions of the body, with the exception of spontaneous respiratory movements, the regulation of blood pressure and heart rhythm. These last functions depend on the medulla oblongata (see Fig. 66). With traumatic brain injury, the so-called “brain death” occurs when all signs of electrical activity of the cortex disappear and control from the hypothalamus and medulla oblongata is lost, although artificial respiration can still maintain sufficient saturation of the circulating blood with oxygen.
continuation
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As you know, a living cell is a mobile, self-regulating system. Its internal organization is supported by active processes aimed at limiting, preventing or eliminating shifts caused by various influences from the environment and the internal environment. The ability to return to the original state after a deviation from a certain average level, caused by one or another "disturbing" factor, is the main property of the cell. A multicellular organism is a holistic organization, the cellular elements of which are specialized to perform various functions. Interaction within the body is carried out by complex regulatory, coordinating and correlating mechanisms with the participation of nervous, humoral, metabolic and other factors. Many individual mechanisms that regulate intra- and intercellular relationships, in some cases, have mutually opposite (antagonistic) effects that balance each other. This leads to the establishment of a mobile physiological background (physiological balance) in the body and allows the living system to maintain relative dynamic constancy, despite changes in the environment and shifts that occur during the life of the organism.
The term "homeostasis" was proposed in 1929 by the physiologist W. Cannon, who believed that the physiological processes that maintain stability in the body are so complex and diverse that it is advisable to combine them under the general name of homeostasis. However, back in 1878, K. Bernard wrote that all life processes have only one goal - to maintain the constancy of living conditions in our internal environment. Similar statements are found in the works of many researchers of the 19th and the first half of the 20th century. (E. Pfluger, S. Richet, L.A. Fredericq, I.M. Sechenov, I.P. Pavlov, K.M. Bykov and others). The works of L.S. Stern (with collaborators), devoted to the role of barrier functions that regulate the composition and properties of the microenvironment of organs and tissues.
The very idea of homeostasis does not correspond to the concept of stable (non-fluctuating) balance in the body - the principle of balance is not applicable to complex physiological and biochemical processes occurring in living systems. It is also wrong to oppose homeostasis to rhythmic fluctuations in the internal environment. Homeostasis in a broad sense covers the issues of cyclic and phase flow of reactions, compensation, regulation and self-regulation of physiological functions, the dynamics of the interdependence of nervous, humoral and other components of the regulatory process. The boundaries of homeostasis can be rigid and plastic, vary depending on individual age, gender, social, professional and other conditions.
Of particular importance for the life of the organism is the constancy of the composition of the blood - the liquid basis of the body (fluid matrix), according to W. Cannon. The stability of its active reaction (pH), osmotic pressure, ratio of electrolytes (sodium, calcium, chlorine, magnesium, phosphorus), glucose content, number of formed elements, and so on are well known. So, for example, blood pH, as a rule, does not go beyond 7.35-7.47. Even severe disorders of acid-base metabolism with a pathology of acid accumulation in the tissue fluid, for example, in diabetic acidosis, have very little effect on the active reaction of the blood. Despite the fact that the osmotic pressure of blood and tissue fluid is subject to continuous fluctuations due to the constant supply of osmotically active products of interstitial metabolism, it remains at a certain level and changes only in some severe pathological conditions.
Maintaining a constant osmotic pressure is of paramount importance for water metabolism and maintaining ionic balance in the body (see Water-salt metabolism). The greatest constancy is the concentration of sodium ions in the internal environment. The content of other electrolytes also fluctuates within narrow limits. The presence of a large number of osmoreceptors in tissues and organs, including in the central nervous formations (hypothalamus, hippocampus), and a coordinated system of regulators of water metabolism and ionic composition allows the body to quickly eliminate shifts in the osmotic blood pressure that occur, for example, when water is introduced into the body .
Despite the fact that blood represents the general internal environment of the body, the cells of organs and tissues do not directly come into contact with it.
In multicellular organisms, each organ has its own internal environment (microenvironment) corresponding to its structural and functional features, and the normal state of organs depends on the chemical composition, physicochemical, biological and other properties of this microenvironment. Its homeostasis is determined by the functional state of histohematic barriers and their permeability in the directions of blood→tissue fluid, tissue fluid→blood.
Of particular importance is the constancy of the internal environment for the activity of the central nervous system: even minor chemical and physicochemical shifts that occur in the cerebrospinal fluid, glia, and pericellular spaces can cause a sharp disruption in the course of life processes in individual neurons or in their ensembles. A complex homeostatic system, including various neurohumoral, biochemical, hemodynamic and other regulatory mechanisms, is the system for ensuring the optimal level of blood pressure. At the same time, the upper limit of the level of arterial pressure is determined by the functionality of the baroreceptors of the vascular system of the body, and the lower limit is determined by the body's needs for blood supply.
The most perfect homeostatic mechanisms in the body of higher animals and humans include the processes of thermoregulation; in homoiothermic animals, fluctuations in temperature in the internal parts of the body during the most dramatic changes in temperature in the environment do not exceed tenths of a degree.
Various researchers explain the mechanisms of a general biological nature that underlie homeostasis in different ways. So, W. Cannon attached special importance to the higher nervous system, L. A. Orbeli considered the adaptive-trophic function of the sympathetic nervous system to be one of the leading factors of homeostasis. The organizing role of the nervous apparatus (the principle of nervism) underlies the well-known ideas about the essence of the principles of homeostasis (I. M. Sechenov, I. P. Pavlov, A. D. Speransky and others). However, neither the dominant principle (A. A. Ukhtomsky), nor the theory of barrier functions (L. S. Stern), nor the general adaptation syndrome (G. Selye), nor the theory of functional systems (P. K. Anokhin), nor the hypothalamic regulation of homeostasis (N. I. Grashchenkov) and many other theories do not completely solve the problem of homeostasis.
In some cases, the concept of homeostasis is not quite rightly used to explain isolated physiological states, processes, and even social phenomena. This is how the terms “immunological”, “electrolyte”, “systemic”, “molecular”, “physico-chemical”, “genetic homeostasis” and the like appeared in the literature. Attempts have been made to reduce the problem of homeostasis to the principle of self-regulation. An example of solving the problem of homeostasis from the point of view of cybernetics is Ashby's attempt (W. R. Ashby, 1948) to design a self-regulating device that simulates the ability of living organisms to maintain the level of certain quantities within physiologically acceptable limits. Some authors consider the internal environment of the body as a complex chain system with many "active inputs" (internal organs) and individual physiological indicators (blood flow, blood pressure, gas exchange, etc.), the value of each of which is due to the activity of the "inputs".
In practice, researchers and clinicians face the issues of assessing the adaptive (adaptive) or compensatory capabilities of the body, their regulation, strengthening and mobilization, predicting the body's response to disturbing influences. Some states of vegetative instability, caused by insufficiency, excess or inadequacy of regulatory mechanisms, are considered as “diseases of homeostasis”. With a certain conventionality, they can include functional disturbances in the normal functioning of the body associated with its aging, forced restructuring of biological rhythms, some phenomena of vegetative dystonia, hyper- and hypocompensatory reactivity under stressful and extreme influences, and so on.
To assess the state of homeostatic mechanisms in fiziol. experiment and in a wedge, practice various dosed functional tests are applied (cold, thermal, adrenaline, insulin, mezaton and others) with definition in blood and urine of a parity of biologically active agents (hormones, mediators, metabolites) and so on.
Biophysical mechanisms of homeostasis
Biophysical mechanisms of homeostasis. From the point of view of chemical biophysics, homeostasis is a state in which all processes responsible for energy transformations in the body are in dynamic equilibrium. This state is the most stable and corresponds to the physiological optimum. In accordance with the concepts of thermodynamics, an organism and a cell can exist and adapt to such environmental conditions under which it is possible to establish a stationary course of physicochemical processes, that is, homeostasis, in a biological system. The main role in establishing homeostasis belongs primarily to cellular membrane systems, which are responsible for bioenergetic processes and regulate the rate of entry and release of substances by cells.
From these positions, the main causes of the disturbance are non-enzymatic reactions that are unusual for normal life activity, occurring in membranes; in most cases, these are chain reactions of oxidation involving free radicals that occur in cell phospholipids. These reactions lead to damage to the structural elements of cells and disruption of the regulatory function. Factors that cause homeostasis disorders also include agents that cause radical formation - ionizing radiation, infectious toxins, certain foods, nicotine, as well as a lack of vitamins, and so on.
One of the main factors stabilizing the homeostatic state and functions of membranes are bioantioxidants, which inhibit the development of oxidative radical reactions.
Age features of homeostasis in children
Age features of homeostasis in children. The constancy of the internal environment of the body and the relative stability of physicochemical parameters in childhood are provided with a pronounced predominance of anabolic metabolic processes over catabolic ones. This is an indispensable condition for growth and distinguishes the child's body from the body of adults, in which the intensity of metabolic processes is in a state of dynamic equilibrium. In this regard, the neuroendocrine regulation of the homeostasis of the child's body is more intense than in adults. Each age period is characterized by specific features of homeostasis mechanisms and their regulation. Therefore, in children much more often than in adults, there are severe violations of homeostasis, often life-threatening. These disorders are most often associated with the immaturity of the homeostatic functions of the kidneys, with disorders of the functions of the gastrointestinal tract or respiratory function of the lungs.
The growth of the child, expressed in an increase in the mass of his cells, is accompanied by distinct changes in the distribution of fluid in the body (see Water-salt metabolism). The absolute increase in the volume of extracellular fluid lags behind the rate of overall weight gain, so the relative volume of the internal environment, expressed as a percentage of body weight, decreases with age. This dependence is especially pronounced in the first year after birth. In older children, the rate of change in the relative volume of extracellular fluid decreases. The system for regulating the constancy of the volume of liquid (volume regulation) provides compensation for deviations in the water balance within fairly narrow limits. A high degree of tissue hydration in newborns and young children determines a significantly higher need for water than in adults (per unit body weight). Loss of water or its limitation quickly lead to the development of dehydration due to the extracellular sector, that is, the internal environment. At the same time, the kidneys - the main executive organs in the system of volume regulation - do not provide water savings. The limiting factor of regulation is the immaturity of the tubular system of the kidneys. The most important feature of the neuroendocrine control of homeostasis in newborns and young children is the relatively high secretion and renal excretion of aldosterone, which has a direct effect on the state of tissue hydration and the function of the renal tubules.
Regulation of the osmotic pressure of blood plasma and extracellular fluid in children is also limited. The osmolarity of the internal environment varies over a wider range (±50 mosm/l) than in adults ±6 mosm/l). This is due to the greater body surface per 1 kg of weight and, consequently, more significant water loss during respiration, as well as the immaturity of the renal mechanisms of urine concentration in children. Homeostasis disorders, manifested by hyperosmosis, are especially common in children during the neonatal period and the first months of life; at older ages, hypoosmosis begins to predominate, associated mainly with gastrointestinal or night diseases. Less studied is the ionic regulation of homeostasis, which is closely related to the activity of the kidneys and the nature of nutrition.
It was previously believed that the main factor determining the value of the osmotic pressure of the extracellular fluid is the concentration of sodium, but more recent studies have shown that there is no close correlation between the sodium content in the blood plasma and the value of the total osmotic pressure in pathology. The exception is plasmatic hypertension. Therefore, homeostatic therapy by administering glucose-salt solutions requires monitoring not only the sodium content in serum or plasma, but also changes in the total osmolarity of the extracellular fluid. Of great importance in maintaining the total osmotic pressure in the internal environment is the concentration of sugar and urea. The content of these osmotically active substances and their effect on water-salt metabolism can increase sharply in many pathological conditions. Therefore, for any violations of homeostasis, it is necessary to determine the concentration of sugar and urea. In view of the foregoing, in children of early age, in violation of the water-salt and protein regimes, a state of latent hyper- or hypoosmosis, hyperazotemia may develop (E. Kerpel-Froniusz, 1964).
An important indicator characterizing homeostasis in children is the concentration of hydrogen ions in the blood and extracellular fluid. In the antenatal and early postnatal periods, the regulation of acid-base balance is closely related to the degree of blood oxygen saturation, which is explained by the relative predominance of anaerobic glycolysis in bioenergetic processes. Moreover, even moderate hypoxia in the fetus is accompanied by the accumulation of lactic acid in its tissues. In addition, the immaturity of the acidogenetic function of the kidneys creates the prerequisites for the development of "physiological" acidosis. In connection with the peculiarities of homeostasis in newborns, disorders often occur that stand on the verge between physiological and pathological.
The restructuring of the neuroendocrine system in puberty is also associated with changes in homeostasis. However, the functions of the executive organs (kidneys, lungs) reach their maximum degree of maturity at this age, so severe syndromes or diseases of homeostasis are rare, but more often we are talking about compensated changes in metabolism, which can only be detected by a biochemical blood test. In the clinic, to characterize homeostasis in children, it is necessary to examine the following indicators: hematocrit, total osmotic pressure, sodium, potassium, sugar, bicarbonates and urea in the blood, as well as blood pH, pO 2 and pCO 2.
Features of homeostasis in the elderly and senile age
Features of homeostasis in the elderly and senile age. The same level of homeostatic values in different age periods is maintained due to various shifts in the systems of their regulation. For example, the constancy of blood pressure at a young age is maintained due to a higher cardiac output and low total peripheral vascular resistance, and in the elderly and senile - due to a higher total peripheral resistance and a decrease in cardiac output. During the aging of the body, the constancy of the most important physiological functions is maintained in conditions of decreasing reliability and reducing the possible range of physiological changes in homeostasis. The preservation of relative homeostasis with significant structural, metabolic and functional changes is achieved by the fact that at the same time not only extinction, disturbance and degradation occurs, but also the development of specific adaptive mechanisms. Due to this, a constant level of sugar in the blood, blood pH, osmotic pressure, cell membrane potential, and so on are maintained.
Changes in the mechanisms of neurohumoral regulation, an increase in the sensitivity of tissues to the action of hormones and mediators against the background of a weakening of nervous influences, are essential in maintaining homeostasis during the aging process.
With the aging of the body, the work of the heart, pulmonary ventilation, gas exchange, kidney functions, secretion of the digestive glands, the function of the endocrine glands, metabolism, and others change significantly. These changes can be characterized as homeoresis - a regular trajectory (dynamics) of changes in the intensity of metabolism and physiological functions with age over time. The value of the course of age-related changes is very important for characterizing the aging process of a person, determining his biological age.
In the elderly and senile age, the general potential of adaptive mechanisms decreases. Therefore, in old age, with increased loads, stress and other situations, the likelihood of disruption of adaptive mechanisms and homeostasis disturbances increase. Such a decrease in the reliability of homeostasis mechanisms is one of the most important prerequisites for the development of pathological disorders in old age.
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The history of the development of the doctrine of homeostasis
K. Bernard and his role in the development of the doctrine of the internal environment
For the first time, homeostatic processes in the body as processes that ensure the constancy of its internal environment were considered by the French naturalist and physiologist C. Bernard in the middle of the 19th century. The term itself homeostasis was proposed by the American physiologist W. Kennon only in 1929.
In the development of the doctrine of homeostasis, the leading role was played by the idea of C. Bernard that for a living organism there are “actually, two environments: one external environment in which the organism is placed, the other internal environment in which tissue elements live.” In 1878, the scientist formulates the concept of the constancy of the composition and properties of the internal environment. The key idea of this concept was the idea that the internal environment is not only blood, but also all the plasma and blastoma fluids that come from it. “The internal environment,” wrote K. Bernard, “... is formed from all the constituent parts of the blood - nitrogenous and nitrogen-free, protein, fibrin, sugar, fat, etc., ... with the exception of blood globules, which are already independent organic elements.”
The internal environment includes only the liquid components of the body, which wash all the elements of tissues, i.e. blood plasma, lymph and tissue fluid. K. Bernard considered the attribute of the internal environment to be “in direct contact with the anatomical elements of a living being”. He noted that when studying the physiological properties of these elements, it is necessary to consider the conditions for their manifestation and their dependence on the environment.
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Claude Bernard (1813-1878)The scientist rightly believed that the manifestations of life are due to the conflict between the existing forces of the body (constitution) and the influence of the external environment. The vital conflict in the body manifests itself in the form of two opposite and dialectically related phenomena: synthesis and decay. As a result of these processes, the body adapts, or adapts, to environmental conditions.
An analysis of the works of K. Bernard allows us to conclude that all physiological mechanisms, no matter how different they may be, serve to maintain the constancy of living conditions in the internal environment. “The constancy of the internal environment is the condition of a free, independent life. This is achieved through a process that maintains in the internal environment all the conditions necessary for the life of the elements. The constancy of the environment presupposes such a perfection of the organism, in which external variables would be compensated and balanced at every moment. For a liquid medium, the main conditions for its constant maintenance were determined: the presence of water, oxygen, nutrients, and a certain temperature.
The independence of life from the external environment, which K. Bernard spoke about, is very relative. The internal environment is closely related to the external one. Moreover, it retained many properties of the primary environment in which life once originated. Living beings, as it were, closed the sea water into a system of blood vessels and turned the constantly fluctuating external environment into an internal environment, the constancy of which is protected by special physiological mechanisms.
The main function of the internal environment is to bring "organic elements into relation with each other and with the external environment." K. Bernard explained that there is a constant exchange of substances between the internal environment and the cells of the body due to their qualitative and quantitative differences inside and outside the cells. The internal environment is created by the organism itself, and the constancy of its composition is maintained by the organs of digestion, respiration, excretion, etc., the main function of which is to "prepare a common nutrient fluid" for the cells of the body. The activity of these organs is regulated by the nervous system and with the help of "specially produced substances." This "consists an uninterrupted circle of mutual influences that form life harmony."
Thus, in the second half of the 19th century, C. Bernard gave the correct scientific definition of the internal environment of the body, singled out its elements, described the composition, properties, evolutionary origin and emphasized its importance in ensuring the life of the body.
The doctrine of homeostasis by W. Kennon
Unlike K. Bernard, whose conclusions were based on broad biological generalizations, W. Kennon came to the conclusion about the importance of the constancy of the internal environment of the body by another method: on the basis of experimental physiological studies. The scientist drew attention to the fact that the life of an animal and a person, despite the fairly frequent adverse effects, proceeds normally for many years.
W. Kennon noted that the constant conditions maintained in the body could be called balance. However, a quite definite meaning was already assigned to this word earlier: it denotes the most probable state of an isolated system, in which all known forces are mutually balanced, therefore, in an equilibrium state, the parameters of the system do not depend on time, and there are no flows of matter or energy in the system. In the body, complex coordinated physiological processes are constantly taking place, ensuring the stability of its states. An example is the coordinated activity of the brain, nerves, heart, lungs, kidneys, spleen and other internal organs and systems. Therefore, W. Kennon proposed a special designation for such states - homeostasis. This word does not at all imply something frozen and motionless. It means a condition that can change, but still remain relatively constant.
Term homeostasis formed from two Greek words: homoios similar, similar and stasis- standing still. In interpreting this term, W. Kennon emphasized that the word stasis implies not only a stable state, but also a condition leading to this phenomenon, and the word homoios indicates the similarity and similarity of phenomena.
The concept of homeostasis, according to W. Kennon, also includes physiological mechanisms that ensure the stability of living beings. This special stability is not characterized by the stability of the processes, on the contrary, they are dynamic and constantly changing, however, under the conditions of the "norm" the fluctuations of physiological parameters are rather severely limited.
Later, W. Kennon showed that all metabolic processes and the main conditions under which the most important vital functions of the body are performed - body temperature, the concentration of glucose and mineral salts in the blood plasma, pressure in the vessels - fluctuate within very narrow limits near certain average values - physiological constants. Maintaining these constants in the body is a prerequisite for existence.
W. Kennon singled out and classified main components of homeostasis. He referred to them materials that provide cellular needs(materials necessary for growth, repair and reproduction - glucose, proteins, fats; water; chlorides of sodium, potassium and other salts; oxygen; regulatory compounds), and physical and chemical factors that affect cellular activity (osmotic pressure, temperature, concentration of hydrogen ions, etc.). At the present stage of development of knowledge about homeostasis, this classification has been replenished mechanisms that ensure the structural constancy of the internal environment of the body and structural and functional integrity the whole organism. These include:
a) heredity;
b) regeneration and reparation;
c) immunobiological reactivity.
conditions automatic maintaining homeostasis, according to W. Kennon, are:
– a flawlessly functioning alarm system that notifies the central and peripheral regulatory devices of any changes that threaten homeostasis;
- the presence of corrective devices that take effect in a timely manner and delay the onset of these changes.
E.Pfluger, Sh.Richet, I.M. Sechenov, L. Frederick, D. Haldane and other researchers who worked at the turn of the 19th–20th centuries also approached the idea of the existence of physiological mechanisms that ensure the stability of the organism, and used their own terminology. However, the term homeostasis, proposed by W. Kennon to characterize the states and processes that create such an ability.
For biological sciences, in understanding homeostasis according to W. Kennon, it is valuable that living organisms are considered as open systems that have many connections with the environment. These connections are carried out through the respiratory and digestive organs, surface receptors, nervous and muscular systems, etc. Changes in the environment directly or indirectly affect these systems, causing appropriate changes in them. However, these effects are usually not accompanied by large deviations from the norm and do not cause serious disturbances in physiological processes.
Contribution of L.S. Stern in the development of ideas about homeostasis
Simultaneously with W. Cannon in 1929 in Russia, the Russian physiologist L.S. Stern. “Unlike the simplest, in more complex multicellular organisms, the exchange with the environment takes place through the so-called environment, from which individual tissues and organs draw the material they need and into which they secrete the products of their metabolism. ... As individual parts of the body (organs and tissues) differentiate and develop, each organ, each tissue must create and develop its own immediate nutrient medium, the composition and properties of which must correspond to the structural and functional features of this organ. This immediate nourishing, or intimate, environment must have a certain constancy to ensure the normal functioning of the washed organ. ... The immediate nutrient medium of individual organs and tissues is intercellular or tissue fluid.
L.S. Stern established the importance for the normal activity of organs and tissues of the constancy of the composition and properties of not only blood, but also tissue fluid. She showed the existence of histohematic barriers- physiological barriers separating blood and tissues. These formations, in her opinion, consist of capillary endothelium, basement membrane, connective tissue, cell lipoprotein membranes. The selective permeability of barriers contributes to the preservation of homeostasis and the known specificity of the internal environment necessary for the normal function of a particular organ or tissue. Proposed and well substantiated by L.S. Stern's theory of barrier mechanisms is a fundamentally new contribution to the study of the internal environment.
Histohematic , or vascular tissue , barrier - this is, in essence, a physiological mechanism that determines the relative constancy of the composition and properties of the own environment of the organ and cell. It performs two important functions: regulatory and protective, i.e. ensures the regulation of the composition and properties of the own environment of the organ and cell and protects it from the intake of substances from the blood that are alien to this organ or the whole organism.
Histohematic barriers are present in almost all organs and have the appropriate names: hematoencephalic, hematoophthalmic, hematolabyrinthic, hematoliquor, hematolymphatic, hematopulmonary and hematopleural, hematorenal, as well as the blood-gonadal barrier (for example, hematotesticular), etc.
Modern concepts of homeostasis
The idea of homeostasis turned out to be very fruitful, and throughout the 20th century. it was developed by many domestic and foreign scientists. However, until now this concept in biological science does not have a clear terminological definition. In the scientific and educational literature, one can find either the equivalence of the terms "internal environment" and "homeostasis", or a different interpretation of the concept of "homeostasis".
The internal environment of the body called the whole set of circulating body fluids: blood, lymph, intercellular (tissue) fluid, washing cells and structural tissues, involved in metabolism, chemical and physical transformations. The components of the internal environment also include the intracellular fluid (cytosol), considering that it is directly the environment in which the main reactions of cellular metabolism take place. The volume of the cytoplasm in the body of an adult is about 30 liters, the volume of the intercellular fluid is about 10 liters, and the volume of blood and lymph occupying the intravascular space is 4–5 liters.
In some cases, the term "homeostasis" is used to refer to the constancy of the internal environment and the body's ability to provide it. Homeostasis is a relative dynamic, fluctuating within strictly defined boundaries, the constancy of the internal environment and the stability (stability) of the basic physiological functions of the body. In other cases, homeostasis is understood as physiological processes or control systems that regulate, coordinate and correct the vital activity of the body in order to maintain a stable state.
Thus, the definition of the concept of homeostasis is approached from two sides. On the one hand, homeostasis is seen as a quantitative and qualitative constancy of physicochemical and biological parameters. On the other hand, homeostasis is defined as a set of mechanisms that maintain the constancy of the internal environment of the body.
An analysis of the definitions available in the biological and reference literature made it possible to single out the most important aspects of this concept and formulate a general definition: homeostasis is a state of relative dynamic equilibrium of a system maintained by self-regulation mechanisms. This definition not only includes knowledge of the relativity of the constancy of the internal environment, but also demonstrates the importance of the homeostatic mechanisms of biological systems that ensure this constancy.
The vital functions of the body include homeostatic mechanisms of a very different nature and action: nervous, humoral-hormonal, barrier, controlling and maintaining the constancy of the internal environment and acting at different levels.
The principle of operation of homeostatic mechanisms
The principle of operation of homeostatic mechanisms that ensure regulation and self-regulation at different levels of the organization of living matter was described by G.N. Kassil. There are the following levels of regulation:
1) submolecular;
2) molecular;
3) subcellular;
4) cellular;
5) liquid (internal environment, humoral-hormonal-ionic relationships, barrier functions, immunity);
6) tissue;
7) nervous (central and peripheral nervous mechanisms, neurohumoral-hormonal-barrier complex);
8) organismic;
9) population (populations of cells, multicellular organisms).
The elementary homeostatic level of biological systems should be considered organismic. Within its boundaries, a number of others are distinguished: cytogenetic, somatic, ontogenetic and functional (physiological) homeostasis, somatic genostasis.
Cytogenetic homeostasis as morphological and functional adaptability expresses the continuous restructuring of organisms in accordance with the conditions of existence. Directly or indirectly, the functions of such a mechanism are performed by the hereditary apparatus of the cell (genes).
Somatic homeostasis- the direction of the total shifts in the functional activity of the body to establish the most optimal relationship with the environment.
Ontogenetic homeostasis- this is the individual development of the organism from the formation of a germ cell to death or the cessation of existence in its former quality.
Under functional homeostasis understand the optimal physiological activity of various organs, systems and the whole organism in specific environmental conditions. In turn, it includes: metabolic, respiratory, digestive, excretory, regulatory (providing an optimal level of neurohumoral regulation under given conditions) and psychological homeostasis.
Somatic genostasis is a control over the genetic constancy of the somatic cells that make up the individual organism.
It is possible to distinguish circulatory, motor, sensory, psychomotor, psychological and even informational homeostasis, which ensures the optimal response of the body to incoming information. Separately, a pathological level is distinguished - diseases of homeostasis, i.e. disruption of homeostatic mechanisms and regulatory systems.
Hemostasis as an adaptive mechanism
Hemostasis is a vital complex of complex interrelated processes, an integral part of the body's adaptive mechanism. In view of the special role of blood in maintaining the basic parameters of the body, it is distinguished as an independent type of homeostatic reactions.
The main component of hemostasis is a complex system of adaptive mechanisms that ensures the fluidity of blood in the vessels and its coagulation in case of violation of their integrity. However, hemostasis not only maintains the liquid state of blood in the vessels, the resistance of the walls of the vessels and stops bleeding, but also affects hemodynamics and vascular permeability, participates in wound healing, in the development of inflammatory and immune reactions, and is related to nonspecific resistance of the organism.
The hemostasis system is in functional interaction with the immune system. These two systems form a single humoral defense mechanism, the functions of which are associated, on the one hand, with the fight for the purity of the genetic code and the prevention of various diseases, and on the other hand, with maintaining the liquid state of blood in the circulatory bed and stopping bleeding in case of violation of the integrity of the vessels. Their functional activity is regulated by the nervous and endocrine systems.
The presence of common mechanisms for "turning on" the body's defense systems - immune, coagulation, fibrinolytic, etc. - allows us to consider them as a single structurally and functionally defined system.
Its features are: 1) the cascade principle of sequential inclusion and activation of factors until the formation of final physiologically active substances: thrombin, plasmin, kinins; 2) the possibility of activation of these systems in any part of the vascular bed; 3) the general mechanism for switching on systems; 4) feedback in the mechanism of interaction of these systems; 5) the existence of common inhibitors.
Ensuring the reliability of the functioning of the hemostasis system, as well as other biological systems, is carried out in accordance with the general principle of reliability. This means that the reliability of the system is achieved by redundancy of control elements and their dynamic interaction, duplication of functions or interchangeability of control elements with a perfect quick return to the previous state, the ability for dynamic self-organization and the search for stable states.
Fluid circulation between cellular and tissue spaces, as well as blood and lymphatic vessels
Cellular homeostasis
The most important place in self-regulation and preservation of homeostasis is occupied by cellular homeostasis. It is also called cell autoregulation.
Neither the hormonal nor the nervous systems are fundamentally capable of coping with the task of maintaining the constancy of the composition of the cytoplasm of an individual cell. Each cell of a multicellular organism has its own mechanism of autoregulation of processes in the cytoplasm.
The leading place in this regulation belongs to the outer cytoplasmic membrane. It ensures the transmission of chemical signals into and out of the cell, changing its permeability, takes part in the regulation of the electrolyte composition of the cell, and performs the function of biological "pumps".
Homeostats and technical models of homeostatic processes
In recent decades, the problem of homeostasis has been considered from the standpoint of cybernetics - the science of purposeful and optimal control of complex processes. Biological systems such as cells, brains, organisms, populations, ecosystems operate according to the same laws.
Ludwig von Bertalanffy (1901–1972)Austrian theoretical biologist, creator of the "general systems theory". From 1949 he worked in the USA and Canada. Approaching biological objects as organized dynamic systems, Bertalanffy gave a detailed analysis of the contradictions between mechanism and vitalism, the emergence and development of ideas about the integrity of the organism and, on the basis of the latter, the formation of systemic concepts in biology. Bertalanffy is responsible for a number of attempts to apply an "organismic" approach (i.e., an approach from the point of view of integrity) in the study of tissue respiration and the relationship between metabolism and growth in animals. The method proposed by the scientist for the analysis of open equifinal (aiming at a goal) systems made it possible to widely use the ideas of thermodynamics, cybernetics, and physical chemistry in biology. His ideas have found application in medicine, psychiatry and other applied disciplines. Being one of the pioneers of the system approach, the scientist put forward the first generalized system concept in modern science, the tasks of which are to develop a mathematical apparatus for describing different types of systems, to establish the isomorphism of laws in various fields of knowledge and to search for means of integrating science (“General Systems Theory”, 1968). These tasks, however, have been realized only in relation to certain types of open biological systems. |
The founder of the theory of control in living objects is N. Wiener. The basis of his ideas is the principle of self-regulation - automatic maintenance of constancy or change according to the required law of the regulated parameter. However, long before N. Wiener and W. Kennon, the idea of automatic control was expressed by I.M. Sechenov: “... in the animal body, regulators can only be automatic, i.e. be put into action by changed conditions in the state or course of the machine (organism) and develop activities by which these irregularities are eliminated. In this phrase, there is an indication of the need for both direct and feedback relationships that underlie self-regulation.
The idea of self-regulation in biological systems was deepened and developed by L. Bertalanffy, who understood a biological system as “an ordered set of interconnected elements”. He also considered the general biophysical mechanism of homeostasis in the context of open systems. Based on the theoretical ideas of L. Bertalanffy in biology, a new direction has developed, called systems approach. The views of L. Bertalanffy were shared by V.N. Novoseltsev, who presented the problem of homeostasis as a problem of controlling the flows of substances and energy that an open system exchanges with the environment.
The first attempt to model homeostasis and establish possible mechanisms for controlling it belongs to W.R. Ashby. He designed an artificial self-regulating device called "homeostat". Homeostat U.R. Ashby was a system of potentiometric circuits and reproduced only the functional aspects of the phenomenon. This model could not adequately reflect the essence of the processes underlying homeostasis.
The next step in the development of homeostatics was made by S. Beer, who pointed out two new fundamental points: the hierarchical principle of building homeostatic systems for managing complex objects and the principle of survivability. S. Beer tried to apply certain homeostatic principles in the practical development of organized control systems, revealed some cybernetic analogies between a living system and complex production.
A qualitatively new stage in the development of this direction came after the creation of a formal homeostat model by Yu.M. Gorsky. His views were formed under the influence of the scientific ideas of G. Selye, who argued that “... if it is possible to include contradictions in models reflecting the work of living systems, and even at the same time to understand why nature, creating living things, went this way, this will be a new breakthrough into the secrets of the living with a great practical output.
Physiological homeostasis
Physiological homeostasis is maintained by the autonomic and somatic nervous system, a complex of humoral-hormonal and ionic mechanisms that make up the physico-chemical system of the body, as well as behavior, in which the role of both hereditary forms and acquired individual experience is great.
The idea of the leading role of the autonomic nervous system, especially its sympathoadrenal department, was developed in the works of E. Gelgorn, B.R. Hess, W. Kennon, L.A. Orbeli, A.G. Ginetsinsky and others. The organizing role of the nervous apparatus (the principle of nervism) underlies the Russian physiological school of I.P. Pavlova, I.M. Sechenov, A.D. Speransky.
Humoral-hormonal theories (the principle of humoralism) were developed abroad in the works of G. Dale, O. Levy, G. Selye, C. Sherrington and others. Russian scientists I.P. Razenkov and L.S. Stern.
The accumulated colossal factual material describing various manifestations of homeostasis in living, technical, social, and ecological systems requires study and consideration from a unified methodological standpoint. The unifying theory that was able to combine all the diverse approaches to understanding the mechanisms and manifestations of homeostasis was functional systems theory created by P.K. Anokhin. In his views, the scientist was based on N. Wiener's ideas about self-organizing systems.
Modern scientific knowledge about the homeostasis of the whole organism is based on understanding it as a friendly and coordinated self-regulating activity of various functional systems, characterized by quantitative and qualitative changes in their parameters during physiological, physical and chemical processes.
The mechanism for maintaining homeostasis resembles a pendulum (scales). First of all, the cytoplasm of the cell should have a constant composition - homeostasis of the 1st stage (see diagram). This is provided by the mechanisms of homeostasis of the 2nd stage - circulating fluids, the internal environment. In turn, their homeostasis is associated with vegetative systems for stabilizing the composition of incoming substances, liquids and gases and the release of end products of metabolism - stage 3. Thus, temperature, water content and the concentration of electrolytes, oxygen and carbon dioxide, and the amount of nutrients are maintained at a relatively constant level. and excreted metabolic products.
The fourth step in maintaining homeostasis is behavior. In addition to expedient reactions, it includes emotions, motivations, memory, and thinking. The fourth stage actively interacts with the previous one, builds on it and influences it. In animals, behavior is expressed in the choice of food, feeding grounds, nesting sites, daily and seasonal migrations, etc., the essence of which is the desire for peace, the restoration of disturbed balance.
So homeostasis is:
1) the state of the internal environment and its property;
2) a set of reactions and processes that maintain the constancy of the internal environment;
3) the ability of the organism to resist changes in the environment;
4) the condition for the existence, freedom and independence of life: “The constancy of the internal environment is the condition for a free life” (K. Bernard).
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Since the concept of homeostasis is a key one in biology, it should be mentioned when studying all school courses: "Botany", "Zoology", "General Biology", "Ecology". But, of course, the main attention should be paid to the disclosure of this concept in the course “Man and his health”. Here are some examples of topics that can be studied using the materials of the article. "Organs. Organ systems, the organism as a whole. "Nervous and humoral regulation of functions in the body". “The internal environment of the body. Blood, lymph, tissue fluid. Composition and properties of blood. "Circulation". "Breath". Metabolism as the main function of the body. "Isolation". "Thermoregulation". |
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