Types of interstate associations. International organizations and unions
The condition for sustainability and stability of the country’s economic development is, i.e. balance between production and consumption, aggregate demand and aggregate supply. However, in market economy the state of equilibrium is periodically disrupted. A certain cyclicity is observed, i.e. repeatability in the functioning of the national economy when periods of economic growth are followed by periods of recession and depression, and then recovery and boom are observed again. Cyclicity can also be defined as movement from one macroeconomic equilibrium to another, from one economic cycle (business cycle) to another.
Economic theory identifies a number of cycles economic development(growth): long-wave cycles expressing long-term fluctuations in economic activity with a period of about 50 years and called “Kondratiev cycles” (named after the Russian economist Nikolai Dmitrievich Kondratiev (1892-1938); normal, or so-called large, industrial cycles with a period from 8 to 12 years (“Juglar cycles”), named after the French economist C. Juglar (1819-1908) for his study of industrial fluctuations in France, Great Britain and the USA: small cycles, or “Kitchin cycles” (named after the American economist who discovered them - J. Kitchin (1861 - 1932), lasting 3-4 years and covering the period necessary for the massive renewal of fixed assets.
Cycle phases
IN classic version the economic cycle is taking shape four phase: recession, depression, rise and boom. The final and initial phase in the development of the cycle is the overproduction of products compared to demand. In turn, overproduction occurs due to excessive investment (this leads to overaccumulation of capital) compared to market capacity.
Overaccumulation of capital leads to excess capacity, an increase in inventory, a slowdown in capital turnover and, as a result, a fall in the income of entrepreneurs and their employees. In turn, this leads to a decrease in aggregate demand for investment and consumer goods and services, and ultimately - to a drop in the growth rate of GDP/ND and even its reduction with all the ensuing consequences - a fall in stock prices, rising unemployment, etc. Coming decline phase.
IN depression phase the decline in production stops, but remains high, a decrease in the interest rate stimulates the demand for capital, this creates the preconditions for the accumulation of capital. A new phase in the cycle begins - climb, in which investment grows, unemployment decreases, demand grows, and there is an increase in the rate of profit and interest rates. Economic growth often develops into boom, When production volume exceeds pre-crisis level. Everyone is employed, unemployment is at its lowest level. accompanied by general growth wages and prices. As a result, actual GDP exceeds potential GDP. Coming inflation gap. The growth of business activity stops. Beyond the boom, a sales problem occurs, production declines, and GDP growth rates sharply decline (Fig. 23.2).
Rice. 23.2. Business cycle model
Terminology for the phases of the cycle may vary. Thus, a decline is often called a recession, a rise is a recovery, and a boom is called prosperity.
Evolution of economic cycles
Industrial cycles were clearly evident already in early XIX V. In 1825, England, which at that time was the economic leader, experienced the first economic crisis. Further economic crises repeated periodically after 8-12 years, gradually taking on a global character.
In the first half of the 20th century. The longest and deepest was the global crisis of 1929-1933. The fall in GDP reached more than 40% in some countries.
The post-war economic cycles were greatly influenced by scientific and technological revolution and state countercyclical regulation of the economy, and then by “ new economy" As a result, the nature of the cycles is changing, including the depth of the crises and the duration of the main phases, the interval between which has been reduced from 8 to 4 years. Moreover, the most destructive crisis was the mid-70s.
In the 90s V developed countries wave-like vibrations were observed production process without a deep decline in production, the severity of the crisis has decreased, and the factors counteracting the decline in production have strengthened. This was especially evident in the dynamics of GDP and industrial production.
Since the late 90s. XX century In the development of the economies of the United States, Japan and the European Union, there was an alternation of periods of recession, stagnation and low growth rates with periods of recovery. So, in 1999 and 2000. Average annual GDP growth in the United States was 4.1%, and in 2001 it increased by only 1.2%. In 2002, the rate of GDP growth in the United States accelerated noticeably, but a weakening of economic activity was observed during these years in most developed and developing countries. The year 2003 was marked by a global economic downturn. According to UN forecasts, in the coming years, growth in the global economy will occur unevenly and at a slow pace.
Heart, this main body, performing important function- maintaining life. The processes that occur in the organ cause the heart muscle to excite, contract and relax, thereby setting the rhythm of blood circulation.
In this article we will take a detailed look at the phases of the cardiac cycle, find out what indicators of activity there are, and also try to understand how the human heart works.
If you have any questions while reading the article, you can ask them to the portal specialists. Consultations are provided free of charge 24 hours a day.
Work of the heart
The activity of the heart consists of a continuous alternation of contraction (systolic function) and relaxation (diastolic function). The change between systole and diastole is called the cardiac cycle.
In a person at rest, the contraction frequency averages 70 cycles per minute and has a duration of 0.8 seconds. Before contraction, the myocardium is in a relaxed state, and the chambers are filled with blood that comes from the veins. At the same time, all valves are open and the pressure in the ventricles and atria is equal. Myocardial excitation begins in the atrium. The pressure rises and due to the difference, blood is pushed out.
Thus, the heart performs a pumping function, where the atria are a container for receiving blood, and the ventricles “indicate” the direction.
It should be noted that the cycle of cardiac activity is provided by the impulse for muscle work. Therefore, the organ has a unique physiology and independently accumulates electrical stimulation. Now you know how the heart works.
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Cycle of cardiac work
Processes occurring during the cardiac cycle include electrical, mechanical and biochemical. The cardiac cycle can be influenced by both external factors (sports, stress, emotions, etc.) and the physiological characteristics of the body, which are subject to change.
The cardiac cycle consists of three phases:
- Atrial systole has a duration of 0.1 second. During this period, the pressure in the atria increases, in contrast to the state of the ventricles, which are relaxed at this moment. Due to the difference in pressure, blood is pushed out of the ventricles.
- The second phase consists of atrial relaxation and lasts 0.7 seconds. The ventricles are excited, and this lasts 0.3 seconds. And at this moment the pressure increases, and blood flows into the aorta and artery. Then the ventricle relaxes again for 0.5 seconds.
- Phase number three is a time period of 0.4 seconds when the atria and ventricles are at rest. This time is called a general pause.
The figure clearly shows the three phases of the cardiac cycle:
At the moment, there is an opinion in the world of medicine that the systolic state of the ventricles contributes not only to the ejection of blood. At the moment of excitation, the ventricles undergo a slight displacement towards the upper region of the heart. This leads to the fact that blood is sucked from the main veins into the atria. At this moment the atria are in a diastolic state, and due to the incoming blood they are stretched. This effect is clearly pronounced in the right stomach.
The portal contains a table “Indicators of cardiac activity”. Viewing and downloading - free
Heartbeat
The frequency of contractions in an adult is in the range of beats per minute. The heart rate of children is slightly higher. For example, in infants the heart beats almost three times faster - 120 times per minute, and babies have a heartbeat of 100 beats per minute. Of course, these are approximate figures, because... due to different external factors the rhythm can last longer or shorter.
The main organ is enveloped in nerve threads that regulate all three phases of the cycle. Strong emotional experiences, physical activity and much more increase impulses in the muscles that come from the brain. Undoubtedly important role Physiology, or rather, its changes, plays a role in the activity of the heart. For example, an increase in carbon dioxide in the blood and a decrease in oxygen gives a powerful boost to the heart and improves its stimulation. If changes in physiology affect the blood vessels, this leads to the opposite effect and the heart rate decreases.
As mentioned above, the work of the heart muscle, and therefore the three phases of the cycle, is influenced by many factors in which the central nervous system is not involved.
Eg, heat the body speeds up the rhythm, and the low one slows it down. Hormones, for example, also have direct impact, because They enter the organ along with the blood and increase the rhythm of contractions.
The cardiac cycle is one of the most complex processes occurring in the human body, because... there are many factors involved. Some of them have a direct impact, others affect indirectly. But the totality of all processes allows the heart to carry out its work.
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The structure of the cardiac cycle is the most important process that supports the functioning of the body. A complex organ with its own generator of electrical impulses, physiology and control of the frequency of contractions – it works all its life. The occurrence of diseases of the organ and its fatigue are influenced by three main factors - lifestyle, genetic trait and environmental conditions.
The main organ (after the brain) is the main link in blood circulation, therefore, it affects all metabolic processes in the body. The heart displays any failure or deviation from the normal state in a split second. Therefore, it is so important for every person to know the basic principles of work (three phases of activity) and physiology. This makes it possible to identify violations in the work of this body.
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- You may suddenly feel weak and tired.
- The pressure is constantly fluctuating.
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Phases of the cardiac cycle
The cardiac cycle is a complex and very important process. It includes periodic contractions and relaxations, which in medical language are called “systole” and “diastole”. Most important organ The human heart (heart), which is in second place after the brain, resembles a pump in its work.
Due to excitation, contraction, conduction, and also automaticity, it supplies blood to the arteries, from where it goes through the veins. Thanks to different pressure V vascular system this pump works without interruption, so the blood moves without stopping.
What it is
Modern medicine explains in sufficient detail what the cardiac cycle is. It all starts with the systolic work of the atria, which takes 0.1 s. Blood flows to the ventricles while they are in the relaxation stage. As for leaflet valves, they open, and semilunar valves, on the contrary, close.
The situation changes when the atria relax. The ventricles begin to contract, this takes 0.3 s.
When this process just begins, all the valves of the heart remain in a closed position. The physiology of the heart is such that while the muscles of the ventricles contract, pressure is created, which gradually increases. This indicator also increases where the atria are located.
If we remember the laws of physics, it will become clear why blood tends to move from a cavity in which there is high pressure to a place where it is lower.
Along the way there are valves that do not allow blood to enter the atria, so it fills the cavities of the aorta and arteries. The ventricles stop contracting, and a moment of relaxation occurs at 0.4 s. In the meantime, blood flows into the ventricles without problems.
The purpose of the cardiac cycle is to maintain the functioning of a person's main organ throughout his life.
The strict sequence of phases of the cardiac cycle fits into 0.8 s. The cardiac pause takes 0.4 s. To fully restore heart function, such an interval is quite enough.
Duration of cardiac work
According to medical data, the heart rate ranges from 60 to 80 per minute if a person is in a calm state - both physically and emotionally. After human activity, heart beats become faster depending on the intensity of the load. By the level of arterial pulse you can determine how many heart contractions occur in 1 minute.
The walls of the artery vibrate as they are affected by high blood pressure in the vessels against the background of the systolic work of the heart. As mentioned above, the duration of the cardiac cycle is no more than 0.8 s. The contraction process in the atrium lasts 0.1 s, where the ventricles last 0.3 s, the remaining time (0.4 s) is spent relaxing the heart.
The table shows the exact data of the heart beat cycle.
Where does blood come from and where does it move?
Phase duration in time
Systolic work of the atrium
Diastolic work of the atria and ventricles
Vein - atria and ventricles
Medicine describes 3 main phases that make up the cycle:
- At first, the atria contract.
- Ventricular systole.
- Relaxation (pause) of the atria and ventricles.
An appropriate time is allocated for each phase. The first takes 0.1 s, the second 0.3 s, and the last phase takes 0.4 s.
At each stage, certain actions occur that are necessary for the proper functioning of the heart:
- The first phase provides complete relaxation ventricles. As for the leaf valves, they open. The semilunar valves close.
- The second phase begins with the atria relaxing. The semilunar valves open and the leaflet valves close.
- When there is a pause, the semilunar valves, on the contrary, open, and the leaflet valves are in the open position. Some of the venous blood fills the area of the atria, and the rest collects in the ventricle.
The general pause before a new cycle of cardiac activity begins is of great importance, especially when the heart is filled with blood from the veins. At this moment, the pressure in all chambers is almost the same due to the fact that the atrioventricular valves are in an open state.
Excitation is observed in the area of the sinoatrial node, as a result of which the atria contract. When contraction occurs, the volume of the ventricles is increased by 15%. After systole ends, the pressure drops.
Heartbeat
For an adult, the heart rate does not go beyond 90 beats per minute. Children's heart rates increase. Heart infant produces 120 beats per minute, in children under 13 years of age this figure is 100. This Common parameters. Everyone’s values are slightly different - less or more, they are influenced by external factors.
The heart is entwined with nerve threads that control the cardiac cycle and its phases. The impulse coming from the brain to the muscle increases as a result of a serious stressful condition or after physical exertion. These can be any other changes in the normal state of a person under the influence of external factors.
The most important role in the work of the heart is played by its physiology, or rather, the changes associated with it. If, for example, the composition of the blood changes, the amount carbon dioxide, there is a decrease in oxygen levels, this leads to a strong shock to the heart. The process of its stimulation intensifies. If changes in physiology affect the blood vessels, then the heart rate, on the contrary, decreases.
The activity of the heart muscle is determined by various factors. The same applies to the phases of cardiac activity. Among these factors is the central nervous system.
For example, elevated body temperatures contribute to an accelerated heart rate, while low ones, on the contrary, slow down the system. Hormones also affect heart rate. Together with the blood, they flow to the heart, thereby increasing the frequency of beats.
In medicine, the cardiac cycle is considered a rather complex process. It is influenced by numerous factors, some directly, others indirectly. But together, all these factors help the heart function properly.
The structure of heart contractions is no less important for human body. She keeps him alive. An organ such as the heart is complex. It has a generator of electrical impulses, a certain physiology, and controls the frequency of strokes. That is why it works throughout the life of the body.
Only 3 main factors can influence it:
- human life activity;
- hereditary predisposition;
- ecological state of the environment.
Numerous body processes are under the control of the heart, especially metabolic processes. In a matter of seconds, it can show violations and non-compliance with the established norm. That is why people should know what the cardiac cycle is, what phases it consists of, what their duration is, as well as physiology.
You can determine possible problems by assessing your heart function. And at the first sign of failure, contact a specialist.
Heartbeat phases
As already mentioned, the duration of the cardiac cycle is 0.8 s. The period of tension involves 2 main phases of the cardiac cycle:
- When asynchronous contractions occur. The period of heart beats, which is accompanied by systolic and diastolic work of the ventricles. As for the pressure in the ventricles, it remains almost the same.
- Isometric (isovolumic) contractions are the second phase, which begins some time after asynchronous contractions. On at this stage the pressure in the ventricles reaches the level at which the atrioventricular valves close. But this is not enough for the semilunar valves to open.
Pressure levels increase, thus the semilunar valves open. This causes blood to begin leaving the heart. The whole process takes 0.25 s. And it has a phase structure consisting of cycles.
- Quick expulsion. At this stage, the pressure increases and reaches its maximum values.
- Slow expulsion. The period when pressure parameters decrease. Once the contractions are over, the pressure will quickly subside.
After the systolic activity of the ventricles ends, a period of diastolic activity begins. Isometric relaxation. This lasts until the pressure rises to optimal parameters in the area of the atrium.
At the same time, the atrioventricular valves open. The ventricles fill with blood. There is a transition to the rapid filling phase. Blood circulation is carried out due to the fact that different pressure parameters are observed in the atria and ventricles.
In other chambers of the heart, pressure continues to fall. After diastole, a slow filling phase begins, the duration of which is 0.2 s. During this process, the atria and ventricles are continuously filled with blood. By analyzing cardiac activity, you can determine how long the cycle lasts.
Diastolic and systolic work take almost the same time. Therefore, the human heart works for half of its life, and rests for the second half. The total duration time is 0.9 s, but due to the fact that the processes overlap each other, this time is 0.8 s.
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Phases of cardiac activity
The heart beats rhythmically. The contraction of the heart causes blood to be pumped from the atria to the ventricles and from the ventricles to the blood vessels, and also creates a difference in blood pressure in the arterial and venous systems, thanks to which the blood moves. The contraction phase of the heart is designated as systole, and the relaxation phase as diastole.
The cardiac cycle consists of atrial systole and diastole and ventricular systole and diastole. The cycle begins with contraction of the right atrium, and immediately the left atrium begins to contract. Atrial systole begins 0.1 s before ventricular systole. During atrial systole, blood cannot flow from the right atrium into the vena cava, since the contracting atrium closes the openings of the veins. The ventricles are relaxed at this time, so venous blood enters the right ventricle through the open tricuspid valve, and arterial blood from the left atrium, which enters it from the lungs, is pushed through the open bicuspid valve into the left ventricle. During this time, blood from the aorta and pulmonary artery cannot enter the heart because the semilunar valves are closed by the blood pressure in these blood vessels.
Then the diastole of the atria begins and as their walls relax, blood from the veins fills their cavity.
Immediately after the end of atrial systole, the ventricles begin to contract. At first, only part of the muscle fibers of the ventricles contracts, while the other part stretches. In this case, the shape of the ventricles changes, but the pressure in them remains the same. This is the phase of asynchronous contraction or change in the shape of the ventricles, which lasts approximately 0.05 s. After complete contraction of all muscle fibers of the ventricles, the pressure in their cavities increases very quickly. This causes the tricuspid and bicuspid valves to close and the openings to the atria to close. The semilunar valves remain closed because the pressure in the ventricles is even lower than in the aorta and pulmonary artery. This phase, in which the muscular wall of the ventricles tenses, but their volume does not change until the pressure in them exceeds the pressure in the aorta and pulmonary artery, is called the isometric contraction phase. It lasts about 0.03 s.
During isometric contraction of the ventricles, the pressure in the atria during their diastole reaches zero and even becomes negative, i.e. less than atmospheric, so the atrioventricular valves remain closed, and the semilunar valves are closed by the reverse flow of blood from the arterial vessels.
Both phases of asynchronous and isometric contractions together constitute the period of ventricular tension. In humans, the semilunar valves of the aorta open when the pressure in the left ventricle reaches 100 m Hg. Art., and the semilunar valves of the pulmonary artery open when the pressure in the right ventricle reaches - 12 mm Hg. Art. In this case, the ejection phase begins, or systolic ejection of blood, in which the blood pressure in the ventricles increases sharply within 0.10-0.12 s (fast ejection), and then, as the blood in the ventricles decreases, the increase in pressure stops and by the end of systole it begins to fall within 0.10-0.15 s (slow ejection).
After the semilunar valves open, the ventricles contract, changing their volume and using some of the tension to work to push blood into the blood vessels (auxotonic contraction). During isometric contraction, the blood pressure in the ventricles becomes greater than in the aorta and pulmonary artery, which causes the opening of the semilunar valves and a phase of rapid and then slow expulsion of blood from the ventricles into the blood vessels. After these phases, a sudden relaxation of the ventricles occurs, their diastole. The pressure in the aorta becomes higher than in the left ventricle, and therefore the semilunar valves close. The time interval between the onset of ventricular diastole and the closure of the semilunar valves is called the protodiastolic period, which lasts 0.04 s.
During diastole, the ventricles relax for approximately 0.08 s with the atrioventricular and semilunar valves closed, until the pressure in them drops below that in the atria, already filled with blood. This is the isometric relaxation phase. Ventricular diastole is accompanied by a drop in pressure in them to zero.
A sharp drop in pressure in the ventricles and an increase in pressure in the atria as their contraction begins opens the tricuspid and bicuspid valves. The phase of rapid filling of the ventricles with blood begins, which lasts 0.08 s, and then, due to a gradual increase in pressure in the ventricles as they are filled with blood, the filling of the ventricles slows down, and a slow filling phase begins for 0.16 s, which coincides with the late diastolic phase.
In humans, ventricular systole lasts about 0.3 s, ventricular diastole - 0.53 s, atrial systole - 0.11 s, atrial diastole - 0.69 s. The entire cardiac cycle lasts an average of 0.8 seconds in humans. The time of total diastole of the atria and ventricles is sometimes called a pause. In the work of the heart of man and higher animals in physiological conditions there is no pause other than diastole, which distinguishes the activity of the heart of humans and higher animals from the activity of the heart of cold-blooded animals.
In a horse, when cardiac activity increases, the duration of one cardiac cycle is 0.7 s, of which atrial systole lasts 0.1 s, ventricular systole lasts 0.25 s, and total cardiac systole lasts 0.35 s. Since the atria are also relaxed during ventricular systole, atrial relaxation lasts 0.6 s, or 90% of the duration of the cardiac cycle, and ventricular relaxation lasts 0.45 s, or 60-65%.
This duration of relaxation restores the performance of the heart muscle.
PHASES OF CARDIAC ACTIVITY;
The heart of a healthy person contracts rhythmically at rest with a frequency of 60-80 beats per minute (in young people - up to 90). For highly trained athletes, the lower limit can reach 45 beats per minute.
Cardiac cycle - a period that includes one contraction and subsequent relaxation . A heart rate at rest greater than 90 beats per minute is called tachycardia, and less than 60 - bradycardia.
At heart rate 70 beats per minute full cycle cardiac activity lasts 0.8-0.86 s. Normally, the heart rhythm is correct.
Arrhythmia– disturbance of the correct heart rhythm. Most types of arrhythmias indicate the development of heart pathology.
Systole- contraction of the heart muscle , diastole - relaxation .
Blood in the cardiovascular system flows in one direction: from the left ventricle, through the systemic circulation to the right atrium, and from the right atrium to the right ventricle, from the right ventricle through the pulmonary circulation to the left atrium, from the left atrium to the left ventricle.
One-way blood flow depends on the valve apparatus of the heart and the sequential contraction of the heart.
The cardiac cycle has three phases: atrial systole, ventricular systole and general pause.
1. Atrial systole - the beginning of each cycle , duration 0.1 s. During systole, the pressure in the atria increases, which leads to the ejection of blood into the ventricles, which at this moment are relaxed, the leaflets of the atrioventricular valves hang down, and blood passes freely from the atria to the ventricles. After the expulsion of blood from the atria, diastole occurs.
2. Ventricular systole – occurs after the end of atrial systole, lasting 0.3 s. During ventricular systole, the atria are already relaxed. Like the atria, both ventricles - right and left - contract simultaneously. Ventricular systole consists of period of tension and period of exile.
Voltage period- ventricular systole begins with contraction of fibers as a result of the spread of excitation throughout the myocardium. This period is short. At the moment, the pressure in the cavities of the ventricles has not yet increased. It begins to increase sharply when excitability covers all fibers. As a result of an increase in intraventricular pressure, the tendon filaments, which are attached at one end to the leaflet valves and the other to the papillary muscles, are stretched and prevent the atrioventricular valve from everting towards the atrium, the valve closes. At this moment, the semilunar valves (aorta, pulmonary artery) are also still closed, and the ventricular cavity remains closed, the volume of blood in it is constant. Excitation of the myocardial muscle fibers leads to an increase in blood pressure in the ventricles and an increase in tension in them. Appearance heartbeat in the fifth left intercostal space is due to the fact that with an increase in myocardial tension, the left ventricle takes on a rounded shape and produces an impact on inner surface chest.
Exile period- blood pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, their valves are pressed against the inner walls. As a result, blood quickly flows into the aorta and pulmonary trunk, and the volume of the ventricles quickly decreases. With a drop in pressure, the semilunar valves close, impeding the reverse flow of blood from the aorta and pulmonary artery, and the ventricular myocardium begins to relax. It's coming again short period, during which the aortic valves are still closed and the atrioventricular valves are not open.
3. Diastole of the atria and ventricles - diastole of the whole heart, duration 0.4 s. Diastole continues until the next atrial systole. Then the cycle of cardiac activity is repeated.
The cardiac cycle lasts 0.8 s. During one heartbeat, the atria contract for 0.1 s and rest for 0.7 s. The ventricles contract for 0.3 s and rest for 0.5 s.
Lecture 11. Circulatory system. Physiology of the heart (phases of cardiac activity, heart sounds, electrocardiogram).
The circulatory system ensures the continuous movement of blood through the vessels. It consists of two sections: the heart and blood vessels. You studied their structure in detail using histology and anatomy. And in the biophysics course we looked at individual mechanisms of their functioning. Therefore, I omit in this lecture many issues, both morphology and function. Moreover, in one of the first lectures we already discussed the functional characteristics of the heart muscle. The purpose of this lecture is to study physiological characteristics the work of the heart, which have special meaning for the clinic.
Phases of cardiac activity. The beginning of the heart's work is atrial systole. The right atrium contracts before the left by 0.01 s due to the fact that the main pacemaker is located in the right atrium. It begins the spread of excitement throughout the heart. The duration of this phase of the heart is 0.1 s. During atrial systole, the pressure in them increases: in the right to 5-8 mm Hg. Art., and in the left – up to 8-15 mm Hg. Blood passes into the ventricles and this is accompanied by the closure of the atrioventricular openings. With the transition of excitation to the atrioventricular node and the conduction system of the ventricles, their systole begins. Ventricular systole occurs simultaneously (the atria are in a state of relaxation at this time). The duration of ventricular systole is about 0.3 s. Ventricular systole begins with a phase of asynchronous contraction. It lasts about 0.05 s and represents the process of propagation of excitation and contraction throughout the myocardium. The pressure in the ventricles remains virtually unchanged. During further contraction, when the pressure in the ventricles increases to a value sufficient to close the antioventricular valves, but not enough to open the semilunar valves, the isometric contraction phase begins. Its duration is up to 0.03 s. Sometimes these phases are combined into one and called the voltage phase (0.05-0.08 s). During this phase, the pressure in the right ventricle increases to approximately Hg. Art., and in the left - up to 150 - 200 mm Hg. Art.
During asynchronous contraction, tension increases (the valves are closed) and the length of the muscle fiber does not change. At the end of the tension phase, the pressure ensures the opening of the semilunar valves and the next phase of ventricular systole begins - the rapid expulsion of blood. During this phase, which lasts from 0.05 to 0.12 s, the pressure reaches its maximum values. Subsequently, the pressure drops to 100 Hg. imm hg in the corresponding ventricles and this moment of their work is called slow expulsion of blood. The duration of this phase of ventricular systole is from 0.13 to 0.20 s. With its end, the pressure drops sharply. In the main arteries, the pressure decreases much more slowly, which ensures the subsequent closure of the semilunar valves and prevents the reverse flow of blood. But this already happens at the moment when the ventricular muscle begins to relax and diastole begins. The period of time from the beginning of ventricular relaxation to the closure of the semilunar valves constitutes the first phase of diastole, which is called protodiastolic.
After it, the diastole phase occurs - a decrease in tension or isometric relaxation. It manifests itself when the valves are still closed and lasts approximately 0.05-0.08 s until the moment when the pressure in the atria is higher than the pressure in the ventricles (2-6 mm Hg), which leads to the opening of the antiventricular valves, followed by through which the blood passes into the ventricle. At first, this happens quickly (in 0.05 s) - the phase of rapid filling of the ventricles with blood, and then slowly (in 0.25 s) - the phase of slow filling of the ventricles with blood. During this phase, there is a continuous flow of blood from the main veins into both the atria and ventricles. And finally, the last phase of ventricular diastole is their filling due to atrial systole (0.1 s). The entire ventricular diastole thus lasts about 0.5 s. If we add up the time of ventricular systole and diastole, we get the time that corresponds to a complete cardiac cycle; in an adult it is 0.8 s.
The duration of the cardiac cycle in newborns is 0.4-0.5 s. The duration of ventricular systole is slightly longer than diastole (0.24 and 0.21 s, respectively). With age, the duration of the cardiac cycle increases accordingly. In infants it is 0.40-0.54 s. The duration of ventricular systole in infants is 0.27 s. In children 7-15 years old it can be even greater. The duration of the cardiac cycle increases mainly due to ventricular diastole.
During the work of the heart, there is a moment when both the atria and ventricles together (simultaneously) are in a state of diastole. This period of heart activity is called a cardiac pause, the duration of which is 0.4 s.
During systole, the heart releases half a liter of blood into the bloodstream. This blood volume is called systolic volume (SV). If we multiply CO by the heart rate (HR), we get the minute volume (MV) of the heart, the value of which is about 4.0 - 5.0 liters.
The CO value in infants is about 10.0 ml. By 6 months, on average, it doubles, by 1 year, it triples. In 8-year-old children, CO is 10 times, and in adults it is 20 times more than in newborns. MO also increases; by one year it is about 1250 ml, by 8 years – 2800 ml.
Heart sounds. These are sound phenomena that accompany the work of the heart. Their occurrence is based on vibrations of various structures of the heart: valves, muscles, vascular wall. Like any vibrations, tones are characterized by intensity (amplitude), frequency and duration. In clinical practice, the methods for determining them are: auscultation - auscultation and graphic recording - phonocardiography.
I tone – systolic – lower and prolonged, occurs in the area of the atrioventricular valves simultaneously with the onset of ventricular systole. Its cause is the closure and tension of the atrioventricular valves, vibrations of the walls of the heart cavities during systole and contraction of the ventricular muscles. The duration of this tone is 0.08-0.25 s, and the frequency is Hz. This tone is heard optimally in the region of the apex of the heart.
II tone – diastolic – higher and shorter. Its duration is 0.04-0.12 s, and its frequency is Hz. Its cause is the vibration of the semilunar valves, sometimes they are so expressive that there is a split tone. This tone is heard in the second intercostal space to the right and left of the sternum.
The third sound - ventricular gallop - is associated with vibrations of the muscular wall of the ventricles when they are stretched (immediately after the second sound). This is sometimes called the fill tone. Most often it is heard or recorded on a phonocardiogram (PCG) in children and athletes. This tone is heard as a weak, dull sound, most often at the apex of the heart (in a lying position) and the sternum area (in a standing position). Registers with FKG.
IV sound - atrial gallop - is associated with contraction of the atria when they actively fill the ventricle with blood. Rarely heard, often recorded on FCG
In newborn children, FCG also has the first and second sounds, and sometimes the third and fourth. In most children of this age, the first tone is shorter and the second tone is longer than in adults. In infants, the relative shortness of the first tone remains. In most children of this age, splitting of the second tone is observed. This occurs due to the slamming of the valves of the aorta and pulmonary artery in different time. In infants, the third and fourth tones are often visible on FCG. With age, the duration of the first tone gradually increases in children. Splitting of the second tone can occur at the age of 1-7 years and in adolescents.
Most wide use in clinical practice received registration and analysis electrical potentials arising from the activity of the heart.
An electrocardiogram is a periodically repeating curve that reflects the course of the process of excitation of the heart over time. Individual elements electrocardiograms (ECG), waves, segments, intervals and complexes, received special names. Each ECG element reflects the spread of the excitation process in certain areas of the heart and has a time (in seconds) and height (in mV) characteristics. Analysis of the ECG, regardless of the lead (you studied their characteristics in detail in the biophysics course), is based on the study of waves (P, Q, R, S, T), intervals (PQ, ST, TP, RR), segments (PQ, ST ) and complexes (P - atrial and QRST - ventricular).
Since the cardiac cycle begins with atrial excitation, the first wave on the ECG is the P wave. It characterizes atrial excitation. Its ascending part is the right atrium, and its descending part is the left atrium. Normally, its characteristics are: duration from 0.07 to 0.11 s, height - from 0.12 to 0.16 mV. In standard lead III it may be absent, biphasic or negative. In positions V 1, V 2 – it is positive, V 3, V 4 – it gradually increases. In unipolar limb leads: aVR is negative, aVL and aVF are positive.
The PQ segment is a straight line segment on the isoelectric axis, from the end of the P wave to the beginning of the Q wave. It characterizes the atrioventricular delay time and is 0.04-0.1 s.
The PQ interval is the ECG section from the beginning of the P wave to the beginning of the Q wave, characterizing the spread of excitation from the atria to the ventricles. The duration of this interval is from 0.12 to 0.21 s.
The Q wave characterizes the excitation of the interventricular septum and papillary muscles. Its normal duration is from 0.02 to 0.03 s, its height is up to 0.1 mV. It may not be present in the first standard lead.
The R wave characterizes the excitation of the main muscles of the ventricles. Its height is 0.8-1.6 mV, duration is from 0.02 to 0.07 s. In chest leads V 1 and V 2 it is small, in positions V 3 and V 4 it increases, and in positions V 5 and V 6 it decreases again.
The S wave characterizes excitation in distant parts of the ventricles. Its height reaches up to 0.1 mV and duration up to 0.02-0.03 s. Sometimes it is absent in standard lead I. In the chest leads V 1 and V 2 it is deep, then it decreases, and in the positions V 5 and V 6 it may be absent.
The ST segment is a straight line segment on the isoelectric line from the end of the S wave to the beginning of the T wave and characterizes the moment when both ventricles are simultaneously excited. Its duration is from 0.1 to 0.15 s.
Wave T – characterizes the process of myocardial repolarization, its height is from 0.4 to 0.8 mV and duration is from 0.1 to 0.25 s. In the standard position I is always positive, in II it is often positive and in III it can be positive, biphasic and negative. In positions V 1 and V 2 it is sometimes negative, and in position aVF it is negative.
TR interval - characterizes the general pause of the heart; its duration is 0.4 s.
RR interval – characterizes the complete cardiac cycle; its duration is 0.8 s.
Complex P is atrial, QRST is ventricular.
Since the excitation of the heart begins from its base, this area is the negative pole, while the area at the apex of the heart is the positive pole. The electromotive force (EMF) of the heart has magnitude and direction. The direction of the EMF is usually called the electrical axis of the heart. Most often, it is located parallel to the anatomical axis of the heart (normogram). The direction of a particular wave on the ECG reflects the orientation of the integral vector. When the vector is directed to the apex of the heart, positive (in relation to the electrical axis) waves are recorded on the ECG, and if it is directed to the base, negative waves are recorded. Due to the specific position of the heart in the chest and the shape of the human body, the electrical lines of force arising between the excited and non-excited areas of the heart are distributed unevenly over the surface of the body. If the electrical axis of the heart becomes horizontal (recumbent heart), then this is called a levogram, and if it is vertical (a hanging heart), it is called a rightogram.
ECG of newborns has the following features. In standard lead I, the R wave is small, and the S wave is deep, its amplitude is 2-3 times greater than the amplitude of the R wave. In standard lead III, on the contrary, the R wave has a large amplitude, and the S wave is small. The electrical axis of the heart is directed to the right (the right axis is a consequence of the relatively large mass of the right ventricular myocardium). In addition, newborns have large P and T waves. The high P wave in them is due to relatively large mass atria. The PQ interval is smaller in newborns (0.11 s) than in adults (0.15 s). The duration of the QRS complex (0.04 s) is also less than in adults (0.08 s).
In infants, due to the preferential growth of the left ventricle, the electrical axis of the heart shifts to the left. From 3-4 months, for some children, the legal grammar is replaced by a normogram. In the 1st year of life, children exhibit both rightograms (45%) and normograms (35%). Levograms are occasionally recorded. In infants, the R waves in leads I and II increase, and in lead III the R wave decreases. The R wave becomes 6 times higher than the P wave.
During the period of early and first childhood (1 year - 7 years), the amplitude of the R wave continues to increase relative to the P wave. The Q wave decreases, and the T wave increases.
In children 4-6 years old, the PQ interval increases significantly and the ventricular complex lengthens slightly. During the period of first childhood, normograms and legalgrams are almost equally common. Levograms are recorded somewhat more often than in infants.
In children 8-12 years old, the difference in the amplitudes of the P wave in standard leads increases (in the first lead there is the largest amplitude, in the third lead the smallest). In lead III, the P wave may be negative. The R wave increases in lead I and decreases in lead III. The electrical axis continues to move to the left.
IN adolescence The ECG approaches the ECG of adults. They often have splitting or jaggedness of the QRS complex in lead III. The ST segment often rises smoothly and becomes a large T wave. In 27% of adolescents, the T wave in lead III is negative. In adolescents, the “vertical type” of the normogram is most often recorded (alpha angle from 71 to 90 o), less often the “intermediate” or “basic” type, and even less often – the rightogram.
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Newcomers to the world of electrics and homeowners sometimes have the question of what is in household electrical wiring. This is due to the need to repair some electrical appliance.
In the situation that has arisen, the master’s highest priority should be compliance with safety regulations, and not the manifestation of applied skills and abilities. Knowledge of the elementary laws of the functioning of current and the processes taking place inside household electrical appliances will not only help to cope with the majority of malfunctions that arise in them, but will also make this process the safest.
Designers and engineers do everything possible to prevent accidents when working with electricity in the home. The consumer's task is to comply with the prescribed standards.
- single phase current;
- two-phase current;
- three-phase current.
Single phase current.
Alternating current, which is obtained by rotating a conductor or a system of conductors connected into one coil in a magnetic flux, is called single-phase alternating current.
As a rule, 2 wires are used to transmit single-phase current. They are called phase and zero, respectively. The voltage between these wires is 220 V.
Single phase power supply. Single phase current can be brought to the consumer by two different ways: 2-wire and 3-wire. In the first (two-wire) one, two wires are used to supply single-phase current. One carries phase current, the other is intended for the neutral wire. Thus, power supply is supplied to almost all houses built in the former USSR. In the second method for summing up single-phase current- add another wire. This wire is called grounding (PE). It is designed to prevent electric shock to a person, as well as to drain leakage currents and prevent devices from breaking.
Two-phase current.
Two-phase electric current is a set of two single-phase currents shifted in phase relative to each other by an angle Pi2 or 90 °.
A clear example of the formation of two-phase current. Let's take two inductance coils and arrange them in space so that their axes are mutually perpendicular, after which we power the system of coils two-phase current, as a result we get two magnetic fluxes in the system. The vector of the resulting magnetic field will rotate at a constant angular velocity, as a result, a rotating magnetic field appears. A rotor with windings made in the form of a short-circuited “squirrel wheel” or a metal cylinder on a shaft will rotate, driving the mechanisms.
They transmit two-phase currents using two wires: two phase and two neutral.
Three-phase current.
Three-phase electrical circuit system is called a system that consists of three circuits in which there are alternating EMFs of the same frequency, shifted in phase relative to each other by 1/3 of the period (φ = 2π/3). Each individual circuit of such a system is briefly called its phase, and the system of three phase-shifted alternating currents in such circuits is simply called three-phase current. Three phase current easily transmitted over long distances. Any pair of phase wires has a voltage of 380 V. A pair - a phase wire and a neutral - has a voltage of 220 V.
Distribution three-phase current By residential buildings performed in two ways: 4-wire and 5-wire. A four-wire connection is made with three phase and one neutral wire. After the distribution board, two wires are used to power sockets and switches - one of the phases and zero. The voltage between these wires will be 220V.
Five-wire connection of three-phase current - a protective grounding wire (PE) is added to the circuit. In a three-phase network, the phases must be loaded as evenly as possible, otherwise phase imbalance may occur. What kind of electrical wiring is used in the house determines what electrical equipment can be included in it. For example, grounding is required if high-power devices are connected to the network - refrigerators, stoves, heaters, electronic household appliances - computers, televisions, water-related devices - Jacuzzis, showers (water is a current conductor). Three-phase current is necessary to power motors (relevant for a private home).
Household electrical wiring.
Initially, electricity is generated at a power plant. Then, through the industrial power grid, it enters the transformer substation, where the voltage is converted to 380 volts. The connection of the secondary windings of the step-down transformer is made according to the “star” circuit: three contacts are connected to the common point “0”, and the remaining three are connected to terminals “A”, “B” and “C”, respectively. For clarity, a picture is provided.
The combined contacts “0” are connected to the grounding loop of the substation. Also here the zero is split into:
- Working zero (shown in blue in the picture)
- PE conductor performing a protective function (yellow-green line)
Zeros and current phases from the output of the step-down transformer they are supplied to the distribution panel of the residential building. The resulting three-phase system is distributed across panels in the entrances. Ultimately, a phase voltage of 220 V and a PE conductor, which performs a protective function, enters the apartment.
So, what is zero? A zero is a current conductor connected to the ground loop of a step-down transformer and serves to create a load from the current phase connected to the opposite end of the transformer winding. In addition, there is a so-called “protective zero” - this is the PE contact described earlier. It serves to drain current when a technical malfunction occurs in the circuit.
This method of connecting residential buildings to the city power grid has been proven for decades, but it is still not ideal. Sometimes malfunctions appear in the above system. Most often, they are associated with poor connection quality in a certain section of the circuit or a complete break in the electrical wire.
What happens in zero and phase when a wire breaks.
A break in an electrical wire is often caused by the technician’s elementary absent-mindedness - forgetting to connect it to a certain device in the house current phase or zero - as easy as shelling pears. In addition, there are frequent cases of zero burnout on the access panel due to the high load on the system.
If the connection between any electrical appliance in the house and the panel is broken, this device stops working - because the circuit is not closed. In this case, it does not matter which wire is broken - zero or .
A similar situation occurs when a gap is observed between the distribution panel apartment building and the switchboard of a specific entrance - all apartments connected to the entrance switchboard will be de-energized.
The situations described above do not cause serious difficulties and do not pose any danger. They are associated with the break of only one conductor and do not pose a threat to the safety of electrical appliances or people in the apartment.
The most dangerous situation is the disappearance of the connection between the grounding loop of the substation and the midpoint to which the load of the in-house electrical panel is connected.
In this case, the electric current will flow through circuits AB, BC, CA, and the total voltage on these circuits is 380 V. In this regard, a very unpleasant and dangerous situation will arise - there may be no voltage at all on one electrical panel, as the owner of the apartment considered it necessary turn off electrical appliances, and on another there will be a high voltage close to 380 volts. This will cause failure of most electrical appliances, because the rated operating voltage for them is 240 volts.
Of course, such situations can be prevented - there are quite expensive solutions for protection against power surges. Some manufacturers build them into their devices.
How to determine zero and phase on your own.
To determine the zero and phase of the current, there are special tester screwdrivers.
It works on the principle of passing low voltage current through the body of the person using it. The screwdriver consists of the following parts:
- Tip for connecting to the phase potential of the socket;
- A resistor that reduces the amplitude of the electric current to safe limits;
- LED that lights up when potential is present current phases in a chain;
- Flat contact to create a circuit through the operator's body.
The principle of working with a tester screwdriver is shown in the picture below.
In addition to test screwdrivers, there are other ways to determine which contact of the socket is connected to and which is zero. Some electricians prefer to use a more accurate tester by using it in voltmeter mode.
The voltmeter needle readings mean:
1. Presence of 220 V voltage between phase and zero
2. No voltage between ground and zero
3. No voltage between phase and zero
Actually, in the latter case the arrow should show 220 V, but in this particular case the central contact of the socket is not connected to ground potential.
Each representative of the fair sex has to deal monthly with the phases of her menstrual cycle, with their own characteristics and characteristic symptoms. These phases are significant stages that are responsible for the reproductive function of the female body. The duration and nature of the menstrual phases are largely individual, but the basics and order of their occurrence remain unchanged and have their corresponding names. This entire significant process is cyclical, and begins with the arrival of menstrual bleeding, which is considered to be the first of the three phases of the menstrual cycle.
Any girl or woman in the age range from puberty to menopause must understand the work of her body and understand the purpose of all three phases of the menstrual cycle. With the help of this knowledge, you can easily calculate the favorable period for conceiving a child or, on the contrary, protect yourself from unwanted pregnancy and some health problems.
Main phases of the cycle
Every month, with regular cyclicity, three alternating phases of the menstrual cycle occur in a woman’s body. They are characterized by a logical sequence and serve one purpose big goal– creating favorable conditions for fertilization of the egg and procreation. The menstrual cycle is divided into three main phases:
- Follicular (first phase);
- Ovulation (second phase);
- Luteal (third phase).
These stages perform the functions based on their name. These phases are based on hormonal regulation, which promotes the process and controls its outcome. The beginning of the menstrual cycle is the beginning of the very first phase - the follicular one, which is what gives rise to such an important process as education and.
The first is the follicular phase
The initial phase of the menstrual cycle is characterized by intensive growth of follicles and the formation of eggs in them. The first day of menstruation marks the start of a new follicular phase of the cycle and intensive production of follicle-stimulating hormone and estrogen begins. IN this period There is a growth of follicles, which a little later will become a container and a place for maturation of the egg.
Estrogen provides support to the follicles and this continues for about 7 days, until one of the follicular vesicles reaches the necessary parameters for the maturation of the egg in it. Further growth is focused only on the egg, and the “extra” follicles stop functioning. A high concentration of estrogen gives a signal for the start of the production of luteinizing hormone, which, in turn, prepares for future ovulation. The duration of the first phase is individual for each woman, but it should not exceed 20 days.
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The second phase is ovulation
The second phase of the menstrual cycle is quite short, but at the same time very significant. Ovulation is the achievement for which the menstrual cycle actually exists. It is intended for the possibility of fertilization and the realization of the main purpose of a woman - procreation. The ability and possibility of fertilization is possible within just 48 hours, and sometimes less. During this short period of 2 days, the woman’s reproductive system faces a responsible task, and if fertilization does not occur, the egg dies.
An increased concentration of luteinizing hormone promotes enhanced maturation and subsequent release of the egg from the follicle. Under its influence, important processes occur that ensure the preparation of the endometrial walls. When the egg reaches full maturity and is ready for fertilization, the follicular vesicle ruptures and the full egg is released into the fallopian tube to fuse with the sperm. In the cavity of the ruptured follicle, intensive growth of the corpus luteum begins, which, in turn, intensively produces progesterone and provides favorable conditions for successful fertilization and implantation of the fertilized egg into the uterine wall. The next cycle can have 2 outcomes, depending on whether fertilization occurred or not.
The third phase is the luteal phase
The development of the third phase of the menstrual cycle can occur in two scenarios: with a fertilized egg or if fertilization has not occurred. This time Special attention is given to the resulting corpus luteum. In case of successful conception, it actively produces luteal hormone, which supports and nourishes the fertilized egg until the placenta is formed. Due to the importance of the purpose of this hormone, the third phase has its characteristic name - luteal. Together with the luteal hormone, active production of progesterone continues during this period, which also takes an active part in supporting the fertilized egg. Ultimately, the harmonious and mutually beneficial production of female hormones ensures complete preparation for fertilization, fusion, and subsequent nutrition and protection of the already fertilized egg.
If fertilization still does not occur, the corpus luteum stops its development and atrophies. The prepared, loosened mucous membrane of the uterus and the dead egg are rejected and come out in the form of menstrual bleeding, which, in turn, already means the beginning of a new, first phase and the entire described process is repeated anew.
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Cycle phases by day
The phases of the menstrual cycle by day are conventionally divided into 3 intervals. The first and third phases are considered the longest. It is interesting that the follicular and ovulation phases have an individual and unfixed duration, and the luteal phase always corresponds in duration - 2 weeks or 14 days. As many people know, the entire menstrual cycle can last from 20 to 35 days, and this will be considered normal. Menstrual bleeding is also individual in nature, but it is mandatory for every lady.
To understand what happens and when during these +/- 28 days, it is necessary to consider the duration of each specific phase.
- The follicular phase is the period from the beginning of menstruation until the egg is fully ready for release from the follicle (ovulation). Depending on the characteristics of the body, it can last from 7 to 20 days. At the beginning of this phase, the woman experiences malaise and discomfort in the lumbar region and lower abdomen. Later, strength is restored and unpleasant symptoms recede.
- – it’s time for the egg to be ready for fertilization. This phase is the shortest and most important. The ability of an egg to fuse with a sperm and fertilize lasts from 20 to 48 hours, which is also highly individual and depends on many factors. Some women feel ovulation and even notice characteristic discharge on their underwear.
- . Regardless of whether fertilization has occurred or not, this phase continues for the last 14 days. If pregnancy does not occur, then its end and, therefore, the beginning of a new cycle will be monthly bleeding. During this period, many ladies suffer from premenstrual syndrome () and experience not the most pleasant physical and psychological symptoms and sensations in their body. If after all menstrual cycle fulfilled its direct purpose, and fertilization is completed, then pregnancy occurs and further actions Female hormones will focus on the growth, nutrition and development of the fetus.
What can affect the cycle shift
The considered phases of menstruation are a very clear and fragile mechanism that can be disrupted due to many factors. The main supporters of these phases are hormones, which mutually replace each other to achieve a single goal - conception and birth of a child. A disruption in the production of any of the hormones will lead to a break in the sequential chain and affect the final outcome and duration of the cycle.
Very few people understand the essence of electricity. Concepts such as “electric current”, “voltage”, “phase” and “zero” are for most dark forest, although we encounter them every day. Let's get a grain of useful knowledge and figure out what phase and zero are in electricity. To teach electricity from scratch, we need to understand the fundamental concepts. We are primarily interested in electric current and electric charge.
Electric current and electric charge
Electric charge is a physical scalar quantity that determines the ability of bodies to be a source of electromagnetic fields. The carrier of the smallest or elementary electric charge is the electron. Its charge is approximately -1.6 to 10 to the minus nineteenth power of Coulomb.
Electron charge is the minimum electrical charge (quantum, portion of charge) that occurs in nature in free, long-lived particles.
Charges are conventionally divided into positive and negative. For example, if we rub an ebonite stick on wool, it will acquire a negative electrical charge (excess electrons that were captured by the atoms of the stick upon contact with the wool).
Static electricity on the hair has the same nature, only in this case the charge is positive (the hair loses electrons).
The main type of alternating current is sinusoidal current . This is a current that first increases in one direction, reaches a maximum (amplitude), begins to decrease, at some point becomes equal to zero and increases again, but in a different direction.
Directly about the mysterious phase and zero
We have all heard about phase, three phases, zero and grounding.
The simplest case electrical circuit – single phase circuit . It only has three wires. Through one of the wires the current flows to the consumer (let it be an iron or hair dryer), and through the other it returns back. The third wire in a single-phase network is earth (or grounding).
The ground wire does not carry a load, but serves as a fuse. In case something gets out of control, grounding helps prevent electric shock. This wire carries excess electricity or “drains” into the ground.
The wire through which current flows to the device is called phase , and the wire through which the current returns is zero.
So, why do we need zero in electricity? Yes, for the same thing as the phase! The current flows through the phase wire to the consumer, and through the neutral wire it is discharged to reverse direction. The network through which alternating current is distributed is three-phase. It consists of three phase wires and one return.
It is through this network that the current flows to our apartments. Approaching directly to the consumer (apartments), the current is divided into phases, and each phase is given a zero. The frequency of changing the direction of current in the CIS countries is 50 Hz.
They operate in different countries different standards voltages and frequencies in the network. For example, a typical household outlet in the United States supplies alternating current with a voltage of 100-127 Volts and a frequency of 60 Hertz.
The phase and neutral wires should not be confused. Otherwise, you can cause a short circuit in the circuit. To prevent this from happening and to prevent you from confusing anything, the wires have acquired different colors.
What color are phase and zero indicated in electricity? Zero is usually blue or blue color, and the phase is white, black or brown. The ground wire also has its own color - yellow-green.
So, today we learned what the concepts of “phase” and “zero” mean in electricity. We will be simply happy if this information was new and interesting for someone. Now, when you hear something about electricity, phase, zero and ground, you will already know what we are talking about. Finally, we remind you that if you suddenly need to calculate a three-phase AC circuit, you can safely contact . With the help of our specialists, even the wildest and most difficult task will be up to you.