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The main physiological changes in the human body that occur during labor
Any type of labor activity is a complex set of physiological processes in which all organs and systems of the human body are involved.
Central nervous system (CNS)
The central nervous system provides coordination of functional changes that develop in the body during work.
All labor movements and their nature depend, on the one hand, on impulses coming from the cerebral cortex, and on the other hand, on impulses coming to the center from the periphery from the muscles.
Even before the start of work in the body, conditionally reflex functional shifts are observed, consisting in an increase in metabolism, in increased heart rate and respiration. At the same time, the conditioned environment is the work environment and environment.
It has been established that the level of energy processes occurring in the muscle is dependent on the impulses emanating from the cerebral cortex. So, the main exchange on a working day is 15-30% higher than on the same exchange on a non-working day, which is associated with signals coming from the usual environment of the upcoming working day. An increase in oxygen consumption begins when the worker has just entered the workshop. Consequently, the working environment is perceived by the central nervous system and the last impulses are sent, which prepared the corresponding organs and systems for the implementation of the shift task.
In the process of production training, a dynamic production stereotype is formed - a system of conditioned reflexes that determines the level of physiological processes in the body. The dynamic production stereotype includes the duration of the implementation of the basic elements, micropause, etc.
In the process of doing work in the central nervous system, excitation processes are amplified. At the same time, the processes of inhibition are deepened, due to which equilibrium is maintained between these main processes. With relatively easy work, such a state can persist throughout the working day, with hard work - from a certain moment in the cerebral cortex, protective inhibition processes begin to prevail.
The phase of the change in the functional state of the central nervous system is determined by the nature and duration of the work performed. In the excitation phase, an increase in the magnitude of conditioned reflexes and an increase in the rate of sensorimotor reactions are observed.
In the inhibition phase, reverse processes are observed: a decrease in the magnitude of conditioned reflexes, a decrease in the rate of sensorimotor reactions. The nature of the changes is determined by the severity, duration of work, as well as the fitness of the person.
Muscular work of varying intensity causes changes in the activity of the cerebral cortex. Severe physical activity often causes a decrease in cortical excitability, a violation of conditioned reflex activity, as well as an increase in the sensitivity threshold of visual, auditory and tactile analyzers.
On the contrary, moderate work improves conditioned reflex activity and reduces perceptions for these analyzers.
Under the influence of nerve impulses flowing from the central nervous system, characteristic for them biochemical and biophysical processes occur in the muscles. Adenosine triphosphoric acid (ATP) is the source of chemical energy that turns into mechanical muscle work. Under the influence of nerve impulses, this acid interacts with the contractile protein structure of the muscle, and actomyosin dissociates into its components, changes in the configuration of protein molecules, the appearance of electric charges, the enzymatic cleavage of ATP by myosin, etc.
It is the complex of all phenomena that leads to a reduction in muscle fiber, in the process of which ions of salts, primarily potassium, calcium and magnesium, are actively involved. During muscle relaxation, the lost ATP phosphorus is again phosphorylated by phosphocreatinin. Then the processes of glycolysis and oxidative breakdown of glucose begin, accompanied by the binding of phosphoric acid, cleaved from ATP in the process of muscle contraction.
The ATP content in the muscle is relatively constant and amounts to 3-5 μmol per 1 g of fresh muscle weight (about 0.25%).
With increasing intensity of the load performed, the amount of oxygen consumed by the muscles per unit time increases. Since there is a direct proportional relationship between the rate of oxygen consumption and the work capacity of an aerobic nature, the intensity of work can therefore be characterized by the rate of oxygen consumption. With a certain, individual load for each person, the maximum possible rate of oxygen consumption is achieved.
For energy supply of muscular work, the oxygen system can use all nutrients as carbohydrates (glycogen, glucose), fats (fatty acids) and proteins (amino acids) as oxidation substrates.
During light work, that is, when oxygen consumption is up to 50% of the maximum value, most of the energy for muscle contraction is generated due to the oxidation of fats. During more difficult work with oxygen consumption of more than 60% of the maximum, a significant part of the energy production is provided by carbohydrates. When work is close in oxygen consumption to the maximum - energy production is carried out only due to carbohydrates.
There is a certain sequence of inclusion and the predominance of various pathways of ATP resynthesis as physical activity is performed.
The creatine kinase pathway of ATP resynthesis provides the initial stage of physical work. It starts very quickly, proceeds as efficiently as possible (ATP molecule from the CF molecule), is anaerobic, and does not produce by-products.
Then glycolysis is turned on. It takes 10-20 seconds to start glycolysis. Glycolysis proceeds anaerobically, has a much greater reserve of power, but is not very effective. As a result of glycolysis, the concentration in the muscles and blood of glycolysis of lactic acid increases significantly.
In the future, the aerobic mechanism of ATP resynthesis gradually begins to prevail.
The final products are water and carbon dioxide. Excess carbon dioxide is removed through the lungs with expired air.
The cardiovascular system
An increase in the demand of working muscles for oxygen and nutrients leads to the fact that during physical labor the activity of the cardiovascular system is noticeably increased, where physical activity causes an increase in minute volume due to more frequent contractions and increased stroke volume of the heart.
The pulse from 60-70 beats per minute at rest becomes more frequent during some types of work up to 90-150 and more. As a rule, in 15-30 seconds after the start (and sometimes reflexively and before work), the pulse quickens, reaches a known value, depending on the power of the work, and keeps at this level throughout the work. This gives the right to recommend a pulse count - heart rate (HR) as a simple and affordable method of monitoring the state of the worker during physical work and the course of recovery processes during rest. As a result of work, the minute volume of blood ejected by the heart can increase from 3-5 to 30-40 liters. 5-30 mmHg maximum blood pressure may increase.
An increase in cardiac output occurs due to more frequent contractions and an increase in stroke (systolic) volume of the heart. The systolic volume of the heart at rest ranges from 60-80 ml, with muscle work, it can double or double. There is a certain relationship between the intensity of work and the pulse rate. So, with light work, the heart rate does not exceed 100-120 beats per minute.
In hard work, the heart rate can reach 140-160 or more beats per minute. During hard work, heart rate rises to a maximum, the magnitude of which varies among different people. With light work and moderate work, heart rate increases and stabilizes at a level that ensures the body's oxygen requirements.
The change in heart rate during work largely depends on fitness. A trained person, ceteris paribus, is always less than an untrained person. In untrained people, an increase in the minute volume of the heart during work is provided mainly due to an increase in the number of heart contractions, in trained people - due to an increase in systolic volume.
After the termination of work, the pulse rate decreases sharply. However, the recovery time of the pulse to its original value is largely determined by the severity of the work performed.
The recovery period is at:
easy work - 2-4 minutes;
moderate severity - 30 min .;
heavy - 65-70 minutes.
The recovery period is due to the accumulation of under-oxidized metabolic products in the working bodies.
Under the influence of impulses from the central nervous system, as well as as a result of the vasodilating action of muscle contraction products (lactic acid), the blood vessels of skeletal muscles expand significantly, a network of muscle capillaries develops, but the capillaries themselves narrow. This ensures better blood supply to the working muscle and removal of metabolic products.
The respiratory system, like the cardiovascular system, at the very beginning of the work reveals significant shifts in the direction of strengthening its activity. Increased ventilation, as well as increased heart rate, can take place in the order of the conditioned reflex and in the pre-working period. The magnitude of pulmonary ventilation, and the nature of breathing depend on both individual characteristics and the degree of training a person.
At rest, the number of breaths per minute is from 8 to 22, and pulmonary ventilation is 4-10 l / min. During operation, oxygen consumption increases 10-15 times. Ventilation during heavy work can be achieved by increasing breathing (30-40 times per minute) and increasing the depth of inspiration (40-60 l / min.). In trained people, an increase in pulmonary ventilation is carried out mainly by increasing the depth of breathing.
The amount of oxygen per minute necessary for the complete oxidation of decay products is called the oxygen request, while the maximum amount of oxygen that the body can receive per minute is the oxygen ceiling.
Typically, the oxygen ceiling during physical work for untrained people is about 3 l / min., And for trained people it can reach 4-5 l / min.
It is important to note that oxygen consumption at the beginning of work increases and only after 2-3 minutes. set at a certain level, i.e. its steady state sets in.
Initially, work is done when the oxygen demand is not fully satisfied, as a result of which oxygen debt is accumulated. This is because the energy processes in the muscle when it is reduced occur instantly, and oxygen delivery does not increase immediately. And only when oxygen delivery meets the oxygen demand, does a steady state of oxygen consumption occur.
Oxygen debt generated at the beginning of work is fully repaid after the cessation of work, during the recovery period. This applies to mild to moderate work. With hard work, oxygen consumption increases all the time until reaching the oxygen ceiling. If the oxygen demand during operation exceeds the oxygen ceiling, then the so-called false steady state occurs; however, oxygen consumption reflects only the oxygen ceiling, and not the true oxygen demand. The recovery period is significantly lengthened.
Restoring oxygen consumption does not mean restoring all body functions. On the contrary, other functions, depending on the state of the cardiovascular, respiratory and other systems, have not yet reached their initial level for a considerable time.
When performing muscular work in the blood, some characteristic phenomena can be noted. In hard physical work, there is an increase in the number of red blood cells, an increase in the amount of hemoglobin and a slight increase in blood viscosity, the number of leukocytes can increase three times. In general, the mass of blood circulating in the body increases due to its exit from the depot - spleen, liver, skin. Similarly, leukocytosis develops mainly due to the release of neutrophils and lymphocytes from the depot. The number of leukocytes can reach 15-20 • 109 / l. 1-2 hours after hard work, secondary leukocytosis is possible due to increased blood formation and the entry of neutrophils into the blood.
Of the biochemical changes in the blood, attention is drawn to the dynamics of sugar content (glucose). Typically, at rest, the blood glucose is 4.4-4.95 mmol / L. At the beginning of the work, the amount of glucose in the blood increases, which is explained by conditioned reflex influences. When doing the usual work, especially by a trained person, the glucose level in the blood decreases slightly, then it rises slightly and keeps at about the same level, due to the fact that the output of sugar from the liver increases.
A pronounced decrease in blood glucose occurs when performing heavy and prolonged work. A glucose level below 3.3 mmol / L indicates hard work and inadequate training.
A drop in sugar level during work should be regarded as an unfavorable fact (depletion or insufficient mobilization of carbohydrate resources). The practical significance of this may consist in recommending a break in work for eating.
When performing work of varying severity, a change in the content of lactic acid in the blood is noted: if it normally contains 1.1-2.8 μmol / l, then with very hard work - 5.6-6.7 μmol / l. Light or moderate work does not cause the accumulation of lactic acid, as it manages to oxidize and resynthesize.
Long-term physical efforts of moderate complexity cause only an initial increase in the content of lactic acid in the blood. A sharp increase in the content of lactic acid is observed during heavy work carried out in conditions of oxygen debt. An increase in the content of lactic acid is accompanied by a simultaneous drop in the reserve alkalinity of the blood. Alkaline blood reserve is an indicator of the ability of blood to bind acidic foods. With short-term intensive work, a decrease in alkaline reserve is noted. In this case, the higher the content of lactic acid, the lower the indicator of alkaline reserve.
It should also be noted that as a result of an increase in the concentration of hydrogen ions, the dissociation of oxyhemoglobin can be accelerated, the voltage of oxygen in the blood plasma and the rate of its transition into the tissue can increase. Due to this, the oxygen utilization rate is significantly increased during work, especially among trained people.
A special role in vascular regulation is played by metabolic products (histamine, adenylic acid, acetylcholine), as well as adrenaline, which constricts the vessels of internal organs, and antidiuretic hormone (vasopressin), which acts on arterioles and capillaries.
The content of carbon dioxide in the blood depends on the content of cations in it and the intensity of pulmonary ventilation: at rest in arterial blood its content is 44.6-54.7, in venous - 48.3-60.4 volume percent.
When performing work, the carbon dioxide content in the blood decreases. This is due to the binding of carbon dioxide to cations and leaching from the blood during hyperventilation.
During operation, a change in body temperature occurs. When performing some types of heavy muscular work, it can reach 38.5-39.3 °.
With intense mental work, the temperature of the scalp can increase.
The increase in heat production in working muscles is accompanied by an increase in heat transfer through the expanding vessels of the skin and by evaporation of sweat.
At the same time, as a slight increase in body temperature during work is a favorable factor stimulating the metabolism, tissue respiration, improving conditions for oxygen utilization, a significant increase in it during work cannot be considered favorable. In this case, an increased breakdown of protein compounds occurs, the working conditions of the cardiovascular system, nerve centers deteriorate, energy consumption for external work increases significantly, perspiration increases, the water-salt regime of the body changes (especially when working in hot shops or when doing heavy physical work) . At the same time, a significant increase in the activity of sweat glands can reduce the excretory function of the kidneys. To replenish moisture losses, workers performing heavy physical work should drink a larger amount of liquid than with light work (up to 4-5 liters per shift).
It should be noted that with severe physical exertion, inhibition of gastric secretion and motor function is possible, as well as a slowdown in digestion and absorption of food.
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