Frederick's experience. Respiratory center, its localization, structure and regulation of activity

Claude Bernard's experience(1851). After cutting the sympathetic nerve on the rabbit's neck, 1-2 minutes. observed significant expansion vessels auricle, which manifested itself in redness of the skin of the ear and an increase in its temperature. When the peripheral end of this cut nerve was irritated, the skin, reddened after cutting the sympathetic fibers, became pale and cold. This occurs as a result of narrowing of the lumen of the ear vessels.

Fig. 12. Bronjest's Experience Gaskell's experiment.

Gaskell used the fact of the influence of temperature on the rate of physiological processes to experimentally prove the leading role of the sinus node in the automation of the heart. If you heat or cool different parts of the frog’s heart, it is revealed that the frequency of its contraction changes only when the sinus is heated or cooled, while changes in the temperature of other parts of the heart (atria, ventricle) affect only the strength of muscle contractions. Experience proves that impulses to contract the heart arise in the sinus node. Levi's experience. There are many examples that the creative work of the human brain also occurs during sleep. Thus, it is known that it was in a dream that the Periodic Table “appeared” to D.I. Mendeleev chemical elements . The decisive experiment with which it was possible to prove the chemical mechanism of transmission, dreamed of the Austrian scientist Otto Levi. He later recalled: “The night before Easter Sunday, I woke up, turned on the light and quickly scribbled a few words on a tiny piece of paper. Then he fell asleep again. At six o'clock in the morning I remembered that I had written down something very important, but I could not make out my sloppy handwriting. The next night, at three o'clock, sleep visited me again. It was an idea for an experiment that would test the truth of the chemical transmission hypothesis that had haunted me for seventeen years. I immediately got up, rushed to the laboratory and performed a simple experiment on the heart of a frog, according to my nightly dream.”

Fig. 15. Experience of O. Levi. A – cardiac arrest due to irritation of the vagus nerve; B – arrest of another heart without irritation of the vagus nerve; 1 - nervus vagus, 2 – stimulating electrodes, 3 – cannula

The effects on the myocardium of nerve impulses coming through the autonomic nerves are determined by the nature of the mediator. The mediator of the parasympathetic nerves is acetylcholine, and the sympathetic nerves are norepinephrine. This was first established by the Austrian pharmacologist O. Levi (1921). He connected two isolated frog hearts to the two ends of the same cannula. Strong irritation of the vagus nerve of one of the hearts caused the arrest of not only the heart innervated by this nerve, but also the other, intact one, associated with the first only with a common cannula solution. Consequently, when the first heart was irritated, a substance was released into the solution that affected the second heart. This substance was called "wagusstoff" and was later found to be acetylcholine. With similar irritation of the sympathetic nerve of the heart, another substance was obtained - “sympathikusshtoff”, which is adrenalin or no-radrenaline, similar in their chemical structure.

In 1936, O. Levy and G. Dale received the Nobel Prize for their discovery of the chemical nature of the transmission of nervous reactions.

Marriott's experience (blind spot detection). The subject holds Marriott's drawing at outstretched arms. Closing his left eye, he looks at the cross with his right eye and slowly brings the drawing closer to the eye. At a distance of approximately 15-25cm, the image of the white circle disappears. This happens because when the eye fixates a cross, the rays from it fall on yellow spot. The rays from the circle, at a certain distance of the pattern from the eye, will fall on the blind spot, and the white circle ceases to be visible.

Fig. 16. Drawing by Mariotte

Matteucci's experience (secondary contraction experience). Two neuromuscular drugs are prepared. The nerve of one preparation is left with a piece of the spine, while in the other a piece of the spine is removed. The nerve of one neuromuscular preparation (with a piece of the spine) is placed using a glass hook on electrodes that are connected to the stimulator. The nerve of the second neuromuscular preparation is thrown onto the muscles of this preparation in the longitudinal direction. The nerve of the first neuromuscular preparation is subjected to rhythmic stimulation, the action potentials arising in the muscle during its contraction cause the excitation of the nerve of the other neuromuscular preparation superimposed on it and the contraction of its muscle.

Rice. 17. Matteucci experience

The Stannius Experience consists in the sequential application of three ligatures (dressings), separating the sections of the frog's heart from each other. The experiment is carried out to study the ability of automation of various parts of the conduction system of the heart.

Fig. 18. Scheme of Stannius’ experiment: 1 – first ligature; 2 – first and second ligatures; 3 – first, second and third ligatures. Dark color the parts of the heart that contract after the application of ligatures are indicated

Sechenov's experiment (Sechenov braking). Braking in the center nervous system was discovered by I.M. Sechenov in 1862. He observed the occurrence of inhibition of spinal reflexes during irritation diencephalon (visual cusps) frogs with a crystal of table salt. Outwardly, this was expressed in a significant decrease in the reflex reaction (increase in reflex time) or its cessation. Removal of the table salt crystal led to the restoration of the initial reflex time.

Fig. 19. Scheme of I.M. Sechenov’s experiment with irritation of the visual tuberosities of a frog. A – successive stages of exposing the frog’s brain (1 – a flap of skin cut above the skull is bent back; 2 – the roof of the skull is removed and the brain is exposed). B – frog brain with a cut line for Sechenov’s experiment (1 – olfactory nerves; 2 – olfactory lobes; 3 – cerebral hemispheres; 4 – cut line passing through the diencephalon; 5 – midbrain; 6 – cerebellum; 7 – medulla oblongata ). B – place of application of table salt crystals

Frederic-Heymans experiment (cross-circulation experiment). In the experiment, some dog carotid arteries (I and II) are ligated, while others are connected crosswise to each other using rubber tubes. As a result, the head of dog I is supplied with blood flowing from dog II, and the head of dog II is supplied with the blood of dog I. If you squeeze the trachea of ​​dog I, then the amount of oxygen in the blood flowing through the vessels of its body will gradually decrease and the amount of carbon dioxide will increase. However, the cessation of oxygen access to the lungs of dog I is not accompanied by an increase in its breathing movements On the contrary, they soon weaken, but dog II begins to have very severe shortness of breath.

Since there is no neural connection between both dogs, it is clear that irritant effect lack of oxygen and excess carbon dioxide is transmitted from the body of dog I to the head of dog II through the blood flow, i.e. . humoral way. The blood of dog I, overloaded with carbon dioxide and poor in oxygen, entering the head of dog II, causes excitation of its respiratory center. As a result, dog II experiences shortness of breath, i.e. increased ventilation of the lungs. At the same time, hyperventilation leads to a decrease (below normal) in the carbon dioxide content in the blood of dog II. This carbon dioxide-depleted blood enters the head of dog I and causes a weakening of the work of its respiratory center, despite the fact that all tissues of this dog, with the exception of those of the head, suffer from severe hypercapnia (excess CO 2) and hypoxia (lack of O 2), caused by the cessation of access of air into her lungs.

Fig.20. Cross-circulation experience

Bell-Magendie Law - afferents to the spinal cord nerve fibers enter into the dorsal (dorsal) roots, and efferent ones exit from spinal cord as part of the anterior (ventral) roots.

Gaskell's Gradient Law of Automation – The degree of automaticity is higher, the closer the section of the conduction system is located to the sinoatrial node (sinoatrial node 60-80 impulses/min., atrioventricular - 40-50 impulses/min., His bundle - 30-40 impulses/min., Purkinje fibers - 20 impulses/min. ).

Rubner's body surface law - The energy expenditure of a warm-blooded organism is proportional to the surface area of ​​the body.

Frank-Starling's Law of the Heart(the law of dependence of the energy of myocardial contraction on the degree of stretching of its constituent muscle fibers) - the more the heart muscle is stretched during diastole, the stronger it contracts during systole. Consequently, the force of heart contraction depends on the initial length of the muscle fibers before the start of their contraction.

Lomonosov-Young-Helmholtz theory of three-component color vision – In the vertebrate retina there are three types of cones, each of which contains a special color-reactive substance. Due to the content of various color-reactive substances, some cones have increased excitability to red, others to green, and others to blue-violet.

Heymans' theory of circular activation currents (theory of excitation propagation along nerves) – when conducting nerve impulse each point of the membrane generates an action potential anew, and thus the excitation wave “runs” along the entire nerve fiber.

Bainbridge reflex– with increasing pressure at the mouths of the vena cava, the frequency and strength of heart contractions increases.

Hering's reflex - reflex decrease in heart rate when holding your breath at the height of a deep breath.

Goltz reflex– a decrease in heart rate or even complete cardiac arrest when the mechanoreceptors of organs are irritated abdominal cavity or peritoneum.

Danini-Aschner reflex(ocular reflex) – decrease in heart rate when pressing on the eyeballs.

Parin reflex– with an increase in pressure in the vessels of the pulmonary circulation, cardiac activity is inhibited.

Dale's principle - one neuron synthesizes and uses the same transmitter or the same transmitters in all branches of its axon (in addition to the main transmitter, as it turned out later, other accompanying transmitters can be released at the axon endings, playing a modulating role - ATP, peptides, etc.).

M.M. Zavadsky’s principle (“plus-minus” interaction)– an increase in the hormone content in the blood leads to inhibition of its secretion by the gland, and a deficiency leads to stimulation of hormone secretion.

Bowditch staircase(1871) - if a muscle is stimulated with impulses of increasing frequency without changing their strength, the magnitude of the contractile response of the myocardium will increase to each subsequent stimulus (but up to a certain limit). Outwardly, it resembles a staircase, so the phenomenon is called the Bowditch staircase ( with increasing frequency of stimulation, the force of heart contractions increases).

The Orbeli-Ginetzinsky phenomenon. If, by stimulating the motor nerve, the frog muscle is brought to the point of fatigue, and then at the same time irritating the sympathetic trunk, the performance of the tired muscle increases. Stimulation of sympathetic fibers by itself does not cause muscle contraction, but changes the condition muscle tissue, increases its susceptibility to impulses transmitted through somatic fibers.

Anrep effect(1972) is that with an increase in pressure in the aorta or pulmonary trunk, the force of heart contractions automatically increases, thereby ensuring the possibility of ejecting the same volume of blood as at the initial value blood pressure in the aorta or pulmonary artery, i.e. the greater the counterload, the greater the force of contraction, and as a result, the constancy of the systolic volume is ensured.

LITERATURE

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2. History of biology. From ancient times to the beginning of the 20th century / ed. S.R. Mikulinsky. –M.: Nauka, 1972.

3. Kovalevsky K.L. Laboratory animals. –M.: Publishing House of the Academy of Medical Sciences of the USSR, 1951.

4. Lalayants I.E., Milovanova L.S. Nobel Prizes in medicine and physiology / New in life, science, technology. Ser. "Biology", No. 4. –M.: Knowledge, 1991.

5. Levanov Yu.M. Facets of genius // Biology at school. 1995. No. 5. – P.16.

6. Levanov Yu.M., Andrey Vezaliy //Biology at school. 1995. No. 6. – P.18.

7. Martyanova A.A., Tarasova O.A. Three episodes from the history of physiology. //Biology for schoolchildren. 2004. No. 4. – P.17-23.

8. Samoilov A.F. Selected works. –M.: Nauka, 1967.

9. Timoshenko A.P. About the Hippocratic Oath, the emblem of medicine and much more // Biology at school. 1993. No. 4. – P.68-70.

10. Wallace R. The World of Leonardo /trans. from English M. Karaseva. –M.: TERRA, 1997.

11. Physiology of humans and animals /ed. A.D. Nozdracheva. Book 1. –M.: graduate School, 1991.

12. Human physiology: in 2 volumes. /ed. B.I. Tkachenko. T.2. – St. Petersburg: Publishing house International Foundation for the Development of Science, 1994.

13. Eckert R. Physiology of Animals. Mechanisms and adaptation: in 2t. –M.: Mir, 1991.

14. Encyclopedia for children. T.2. –M.: Publishing house “Avanta +”, 199

The main humoral stimulator of the respiratory center is excess carbon dioxide in the blood, as demonstrated in the experiments of Frederick and Holden.

Frederick's experience on two dogs with cross circulation. In both dogs (first and second), the carotid arteries are cut and cross-connected. The same is done with the jugular veins. The vertebral arteries are ligated. As a result of these operations, the head of the first dog receives blood from the second dog, and the head of the second dog from the first. In the first dog, the trachea is blocked, which causes hyperventilation (frequent and deep breathing) in the second dog, whose head receives blood from the first dog, depleted in oxygen and enriched in carbon dioxide. The first dog has apnea; blood enters its head with a lower CO2 voltage and approximately with the usual, normal content 0 2 - hyperventilation washes away CO 2 and has virtually no effect on the content of 0 2 in the blood, since hemoglobin is saturated

0 2 almost completely and without hyperventilation.

The results of Frederick's experiment indicate that the respiratory center is excited either by an excess of carbon dioxide or by a lack of oxygen.

In Holden's experiment in a closed space from which CO 2 is removed, breathing is weakly stimulated. If CO2 is not removed, shortness of breath is observed - increased and deepening of breathing. Later it was proven that an increase in CO 2 content in the alveoli by 0.2% leads to an increase in lung ventilation by 100%. An increase in the content of CO 2 in the blood stimulates respiration both due to a decrease in pH and the direct effect of CO 2 itself.

The effect of CO 2 and H + ions on respiration is mediated mainly by their effect on special structures of the brain stem that are chemosensitive (central chemoreceptors). Chemoreceptors that respond to change gas composition blood are found externally in the walls of blood vessels in only two areas - in the aortic arch and the sinocarotid region.

The role of aortic and sinocarotid chemoreceptors in the regulation of respiration has been shown experimentally with voltage reduction 0 2 V arterial blood(hypoxemia) below 50-60 mm Hg. Art. - at the same time, ventilation of the lungs increases within 3-5 s. Such hypoxemia can occur when climbing to a height, with cardiopulmonary pathology. Vascular chemoreceptors are also excited by normal voltage blood gases, their activity increases greatly during hypoxia and disappears during breathing pure oxygen. Stimulation of respiration when voltage decreases 0 2 is mediated exclusively by peripheral chemoreceptors. Carotid chemoreceptors are secondary - these are bodies synaptically associated with afferent fibers of the carotid nerve. They are excited by hypoxia, a decrease in pH and an increase in Pco 2, while calcium enters the cell. Their mediator is dopamine.

The aortic and carotid bodies are also excited when the CO2 voltage increases or when the pH decreases. However, the effect of CO 2 from these chemoreceptors is less pronounced than the effect of 0 2 .

Hypoxemia (decreased partial pressure of oxygen in the blood) stimulates breathing much more if it is accompanied hypercapnia, which is observed during very intense physical work: hypoxemia increases the response to CO 2. However, with significant hypoxemia, due to a decrease in oxidative metabolism, the sensitivity of central chemoreceptors decreases. Under these conditions, a decisive role in stimulating respiration is played by vascular chemoreceptors, whose activity increases, since for them adequate stimulus is a decrease in 0 2 voltage in arterial blood (emergency mechanism for stimulating respiration).

Thus, vascular chemoreceptors respond predominantly to a decrease in oxygen levels in the blood, central chemoreceptors - to changes in the blood and cerebrospinal fluid pH and PCO g

The importance of pressoreceptors of the carotid sinus and aortic arch. An increase in blood pressure increases afferent impulses in the sinocarotid and aortic nerves, which leads to some depression of the respiratory center and a weakening of pulmonary ventilation. On the contrary, breathing increases somewhat with a decrease in blood pressure and a decrease in afferent impulses into the brain stem from vascular pressoreceptors.

Breathing regulation - this is the coordinated nervous control of the respiratory muscles, which sequentially carry out respiratory cycles consisting of inhalation and exhalation.

Respiratory center - this is a complex multi-level structural and functional formation of the brain that carries out automatic and voluntary regulation of breathing.

Breathing is an automatic process, but it is subject to voluntary regulation. Without such regulation, speech would be impossible. At the same time, breathing control is based on reflex principles: both unconditional reflex and conditioned reflex.

Breathing regulation is based on general principles automatic regulation that are used in the body.

Pacemaker neurons (neurons are “rhythm creators”) provide automatic the occurrence of excitation in the respiratory center even if the respiratory receptors are not irritated.

Inhibitory neurons provide automatic suppression of this excitation after a certain time.

The respiratory center uses the principle reciprocal (i.e. mutually exclusive) interaction of two centers: inhalation And exhalation . Their arousal is inversely proportional. This means that the excitation of one center (for example, the inhalation center) inhibits the second center associated with it (the exhalation center).

Functions of the respiratory center
- Providing inspiration.
- Providing exhalation.
- Ensuring automatic breathing.
- Ensuring adaptation of breathing parameters to conditions external environment and body activity.
For example, when the temperature increases (as in environment, and in the body) breathing becomes more frequent.

Respiratory center levels

1. Spinal (in the spinal cord). The spinal cord contains centers that coordinate the activity of the diaphragm and respiratory muscles - L-motoneurons in the anterior horns of the spinal cord. Diaphragmatic neurons are in the cervical segments, intercostal neurons are in the thoracic segments. When the pathways between the spinal cord and brain are cut, breathing is disrupted because spinal centers do not have autonomy (i.e. independence) And do not support automation breathing.

2. Bulbar (in the medulla oblongata) - main department respiratory center. In the medulla oblongata and the pons there are 2 main types of neurons of the respiratory center - inspiratory(inhalation) and expiratory(exhalatory).

Inspiratory (inhalation) - are excited 0.01-0.02 s before the start of active inspiration. During inhalation, their pulse frequency increases and then immediately stops. They are divided into several types.

Types of inspiratory neurons

By influence on other neurons:
- inhibitory (stop inhalation)
- facilitating (stimulating inhalation).
By time of excitation:
- early (a few hundredths of a second before inhalation)
- late (active throughout the entire inhalation process).
By connections with expiratory neurons:
- in the bulbar respiratory center
- V reticular formation medulla oblongata.
In the dorsal nucleus, 95% are inspiratory neurons, in the ventral nucleus - 50%. The neurons of the dorsal nucleus are connected to the diaphragm, and the ventral nucleus is connected to the intercostal muscles.

Expiratory (exhalation) - excitation occurs a few hundredths of a second before the start of exhalation.

There are:
- early,
- late,
- expiratory-inspiratory.
In the dorsal nucleus, 5% of neurons are expiratory, and in the ventral nucleus - 50%. In general, there are significantly fewer expiratory neurons than inspiratory neurons. It turns out that inhalation is more important than exhalation.

Automatic breathing is ensured by complexes of 4 neurons with the obligatory presence of inhibitory ones.

Interaction with other brain centers

Respiratory inspiratory and expiratory neurons have output not only to the respiratory muscles, but also to other nuclei of the medulla oblongata. For example, when the respiratory center is excited, the swallowing center is reciprocally inhibited and at the same time, on the contrary, the vasomotor center for regulating cardiac activity is excited.

At the bulbar level (i.e. in the medulla oblongata) it is possible to distinguish pneumotaxic center , located at the level of the pons, above the inspiratory and expiratory neurons. This center regulates their activity and provides a change in inhalation and exhalation. Inspiratory neurons provide inspiration and, at the same time, excitation from them enters the pneumotaxic center. From there, the excitation runs to the expiratory neurons, which are excited and provide exhalation. If you cut the paths between the medulla oblongata and the pons, the frequency of respiratory movements will decrease, due to the fact that the activating effect of the PTDC (pneumotaxic respiratory center) on inspiratory and expiratory neurons is reduced. This also leads to a lengthening of inspiration due to the long-term preservation of the inhibitory effect of expiratory neurons on inspiratory neurons.

3. Suprapontial (i.e. "above-pontine") - includes several areas of the diencephalon:
Hypothalamic region - when irritated, causes hyperpnea - an increase in the frequency of respiratory movements and depth of breathing. The posterior group of hypothalamic nuclei causes hyperpnea, the anterior group acts in the opposite way. It is through the respiratory center of the hypothalamus that breathing responds to ambient temperature.
The hypothalamus, together with the thalamus, ensures changes in breathing during emotional reactions.
Thalamus - provides changes in breathing during pain.
Cerebellum - adapts breathing to muscle activity.

4. Motor and premotor cortex cerebral hemispheres brain. Provides conditioned reflex regulation of breathing. In just 10-15 combinations you can develop a respiratory conditioned reflex. Due to this mechanism, for example, athletes experience hyperpnea before a start.
Asratyan E.A. in his experiments he removed these areas of the cortex from animals. At physical activity they quickly developed shortness of breath - dyspnea, because... they lacked this level of breathing regulation.
The respiratory centers of the cortex enable voluntary changes in breathing.

Regulation of the activity of the respiratory center
The bulbar section of the respiratory center is the main one; it ensures automatic breathing, but its activity can change under the influence humoral And reflex influences

Humoral influences on the respiratory center
Frederick's Experience (1890). He did cross circulation in two dogs - the head of each dog received blood from the body of the other dog. In one dog, the trachea was clamped, consequently, the level of carbon dioxide increased and the level of oxygen in the blood decreased. After this, the other dog began to breathe rapidly. Hyperpnea occurred. As a result, the level of CO2 in the blood decreased and the level of O2 increased. This blood flowed to the first dog's head and inhibited its respiratory center. Humoral inhibition of the respiratory center could lead this first dog to apnea, i.e. stopping breathing.
Factors that humorally affect the respiratory center:
Excess CO2 - hypercarbia, causes activation of the respiratory center.
Lack of O2 - hypoxia, causes activation of the respiratory center.
Acidosis - accumulation of hydrogen ions (acidification), activates the respiratory center.
Lack of CO2 - inhibition of the respiratory center.
Excess O2 - inhibition of the respiratory center.
Alkolosis - +++inhibition of the respiratory center
The neurons of the medulla oblongata themselves count high activity produce a lot of CO2 and locally affect themselves. Positive feedback (self-reinforcing).
In addition to the direct effect of CO2 on the neurons of the medulla oblongata, there is a reflex effect through reflexogenic zones of cardio-vascular system(Reimans reflexes). With hypercarbia, chemoreceptors are excited and from them excitation flows to the chemosensitive neurons of the reticular formation and to the chemosensitive neurons of the cerebral cortex.
Reflex effect on the respiratory center.
1. Constant influence.
Gehling-Breuer reflex. Mechanoreceptors in lung tissues and respiratory tract are excited when the lungs stretch and collapse. They are sensitive to stretching. From them, impulses along the vagus (vagus nerve) go to the medulla oblongata to the inspiratory L-motoneurons. Inhalation stops and passive exhalation begins. This reflex ensures the change of inhalation and exhalation and maintains the activity of the neurons of the respiratory center.
When the vacus is overloaded and cut, the reflex is canceled: the frequency of respiratory movements decreases, the change in inhalation and exhalation is carried out abruptly.
Other reflexes:
stretching of the lung tissue inhibits subsequent inhalation (expiratory facilitation reflex).
Stretching of the lung tissue when inhaling beyond normal level causes an additional sigh (Head's paradoxical reflex).
Heymans reflex - arises from the chemoreceptors of the cardiovascular system to the concentration of CO2 and O2.
Reflex influence from the propreoreceptors of the respiratory muscles - when the respiratory muscles contract, a flow of impulses arises from the propreoreceptors to the central nervous system. According to the feedback principle, the activity of inspiratory and expiratory neurons changes. With insufficient contraction of the inspiratory muscles, a respiratory-facilitating effect occurs and inhalation increases.
2. Fickle
Irritant - located in the respiratory tract under the epithelium. They are both mechano- and chemoreceptors. They have a very high irritation threshold, so they work in extraordinary cases. For example, when pulmonary ventilation decreases, lung volume decreases, irritant receptors are excited and cause a forced inhalation reflex. As chemoreceptors, these same receptors are excited by biologically active substances - nicotine, histamine, prostaglandin. There is a feeling of burning, tickling and in response - a protective cough reflex. In case of pathology, irritant receptors can cause spasm of the airways.
in the alveoli, juxta-alveolar and juxta-capillary receptors react to lung volume and biologically active substances in capillaries. Increases breathing rate and contracts bronchi.
On the mucous membranes of the respiratory tract there are exteroceptors. Coughing, sneezing, holding your breath.
The skin contains heat and cold receptors. Breath holding and breathing activation.
Pain receptors - short-term holding of breath, then intensification.
Enteroreceptors - from the stomach.
Propreoreceptors - with skeletal muscles.
Mechanoreceptors - from the cardiovascular system.

Have you heard about such an experiment on wine experts? I was once in France, where we tried 10-15 varieties of cognac costing from 100 to 10,000 dollars per bottle - I couldn’t distinguish anything there at all. Firstly, I’m not a specialist at all and don’t have any rich drinking experience, and secondly, cognac is still a strong thing.

But what they write about experiments with wine seems to me to be very exaggerated, simplistic, or their experts are so worthless. See for yourself.

Once upon a time, a wine tasting was held in Boston, in which famous connoisseurs of this drink took part. The rules for wine tasting were very simple. Twenty-five of the best wines, the price of which should not exceed $12, were purchased in a regular store in Boston. Later, a group of experts was formed to evaluate red and white wines, who were supposed to blindly identify the best wine from the presented...

As a result, the winner was the cheapest wine. This once again confirms that tasters and wine critics are a myth. Based on the results of the analysis of the experts' responses, it was revealed that all tasters chose the wine that they simply liked the most in taste. So much for the "experts".

By the way, in 2001, Frederic Brochet from the University of Bordeaux conducted two separate and very revealing experiments on tasters. In the first test, Brochet invited 57 experts and asked them to describe their impressions of just two wines.

In front of the experts were two glasses, with white and red wine. The trick was that there was no red wine, in fact it was the same white wine, tinted food coloring. But that didn't stop experts from describing "red" wine in the language they usually use to describe red wines.

One expert praised its "jamminess" and another even "felt" the "crushed red fruit." No one noticed that it was actually white wine!!!

Brochet's second experiment turned out to be even more damning for critics. He took regular Bordeaux and bottled it in two different bottles with different labels. One bottle was grand cru, the other was regular table wine.

Even though they actually drank the same wine, the experts rated them differently. The Grand Cru was "pleasant, woody, complex, balanced and enveloping" and the table was, according to experts, "weak, tasteless, unsaturated, simple."

At the same time, most of them did not even recommend “table” wine for consumption.
Experts are fashion indicators and their taste is no different from their sense of taste ordinary person. People just want to listen to someone’s opinion, that’s what an “expert” is for.

The question arises: Do “experts” exist? In other words, we are different people, and our tastes vary just like brands of cheap wine; some people like them, others don’t.

Or, if not the brand and year of harvest, then white and red wine can be accurately distinguished even by a weak expert? How do you feel about wine experts?

For the normal course of tissue metabolism, the O content is especially important 2 and CO 2 in arterial blood.

Regulation of external respiration

Ventilation of the lungs is the process of updating the gas composition of alveolar air, which ensures the supply of oxygen and the removal of carbon dioxide. This process is carried out by the rhythmic work of the respiratory muscles, changing the volume chest. The intensity of ventilation is determined by the depth of inspiration and breathing frequency. Thus, the minute volume of respiration is an indicator of pulmonary ventilation, which should ensure the gas homeostasis that is necessary in a specific situation (rest, physical work). Regulation of external respiration is the process of changing the minute volume of respiration in different conditions to ensure optimal gas composition internal environment body.

In the second half of the 19th century, a hypothesis appeared that the main factors in the regulation of respiration are the partial pressure of oxygen and carbon dioxide in the alveolar air and, consequently, in the arterial blood. Experimental evidence that enrichment of arterial blood with carbon dioxide and depletion of oxygen enhances ventilation of the lungs as a result of the resulting excitation of the respiratory center was obtained in Frederick's classic experiment with cross-circulation in 1890 (Figure 13). In two anesthetized dogs, the carotid arteries and separately the jugular veins were cut and cross-connected. After such connection and ligation of the vertebral arteries, the head of the first dog was supplied with blood from the second and vice versa. If the trachea was blocked in the first dog and asphyxia was caused in this way, then the second dog developed hyperpnea- increased pulmonary ventilation. In the first dog, despite an increase in carbon dioxide tension in the blood and a decrease in oxygen tension, after some time there occurred apnea- cessation of breathing movements. This is explained by the fact that the carotid artery of the first dog receives blood from the second dog, in which, as a result of hyperventilation, the carbon dioxide content in the arterial blood decreases. Even then it was established that the regulation of breathing occurs through feedback: deviations in the gas composition of arterial blood lead, by influencing the respiratory center, to such changes in breathing that reduce these deviations.

Figure 13. Schematic of Frederick's cross-circulation experiment.

Tracheal compression in Dog A causes shortness of breath in Dog B. Shortness of breath in Dog B causes breathing to slow and stop in Dog A

At the beginning of the 19th century, it was shown that in the medulla oblongata at the bottom of the fourth ventricle there are structures, the destruction of which by a needle prick leads to the cessation of breathing and the death of the body. This small area of ​​the brain in the lower corner of the rhomboid fossa was called the respiratory center.

Numerous studies have established that changes in the gas composition of the internal environment affect the respiratory center not directly, but by influencing special chemosensitive receptors located in the medulla oblongata - central (medullary) chemoreceptors and in vascular reflexogenic zones - peripheral (arterial) chemoreceptors.

During evolutionary development, the main function in stimulating the respiratory center moved from peripheral chemoreceptors to central ones. We are talking primarily about bulbar chemosensitive structures that respond to changes in the concentration of hydrogen ions and CO tension 2 in the extracellular fluid of the brain. Behind peripheral, arterial chemoreceptors, which are also excited when CO tension increases 2 , and with a decrease in oxygen tension in the blood washing them, only an auxiliary role in stimulating breathing remained.

Therefore, let us first consider the central chemoreceptors, which have a more pronounced effect on the activity of the respiratory center.