Тексты для мединститута 6 (перевод)
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качественный перевод текстов преподавателем английского языка, также продаётся по частям
Text B. Conditioned Reflexes
All the visceral and somatic reflexes including the protective, feeding and others are formed by various internal and external stimuli. These stimuli produce reactions not depending on surrounding conditions. The great Russian physiologist Pavlov called them nnconditioned reflexes.
In human beings the nervous system has the additional ability to form cortical associations which increase the range of reactions. This function is obtained by all the human beings and formed upon signalization, i.e. the process in which an ineffective reflex stimulus forms the same reactions as the stimulus with which it has become associated. Pavlov called these individually obtained reflexes conditioned, because they are developed only in connection with some other reflexes.
It is through constant contacts of life that men develop many conditioned reflexes. They begin to develop already in infancy. During human development their number is much increased through training and education.
In experimental conditions it was determined by Pavlov that many new conditioned reflexes to stimuli not supplied by Nature could be established in dogs. But such stimuli had to be associated with those which formed an unconditioned response. Pavlov determined that in higher animals it was in the cortex that conditioned reflexes were formed.
The nervous cells of the cortex are the most delicate of all the cells of the human body.
It is at the moment of tiredness of the cortical nervous cells that the process of inhibition begins to act. This process does not allow new stimuli to pass to the tired areas of the brain. To provide the smooth work of the brain the nervous cells must be well supplied with oxygen and feeding substances. And for this purpose any human being must have regular complete rest, i.e. sleep.
When the process of inhibition extends over a great number of cells, spreads widely over the cortex and even over the subcortical areas of the brain one falls asleep.
When one sleeps the vital activity of the nervous system is restored. So sleep is of a great protective significance to the human being.
The man sleeps about one third of his life. Numerous investigations and experiments have shown that sleep is more necessary for the human being than food. One can live longer without food than without sleep.
During a sound quiet sleep the whole activity of the human organism changes, the body metabolism decreases, the respiratory and pulse rates become slower, the body temperature drops. Though the stimuli continue to come into the brain, ....
One of the scientific research institutes in Chechoslovakia carried out an interesting experiment. Six young persons—four men and two girls did not sleep for 124 hours. They were under the constant observation of the doctors who took their cardiograms, determined the pulse and blood pressure and carried out many other investigations.
Not to fall asleep they were allowed to do physical exercises, dance and play, but they were not allowed to take any stimulants. Vision, hearing and various reflexes were often examined during the experiment.
The experiment was successful. Its findings showed that prolonged sleeplessness increased the amount of sugar in the blood, decreased the level (amount) of vitamins B, and B6, produced considerable increase of white blood cells and decreased the amount of iron in the blood.
Text A. The blood vessels, large and small
The raw material’s1 for the energy that powers man’s every thought and action are transported in the blood. The enriched2 blood id carried in a network of small vessels, capillaries, to each cell. These capillaries are so small that 60 long ones or 120 short ones would stretch only the length of this line of type. There are so many capillaries in the body that, laid end to end, they would ring the equator3 more than twice.
Blood coming into the capillaries from the arteries has been enriched with oxygen in the lungs or with food from the digestive system. The walls of the capillaries are only one cell thick; so thin that oxygenated blood is able, to pass its oxygen and food to the body’s cells and to receive from the cells their waste. The spent blood then flows from the capillaries into the veins, which direct it back to the heart. In the heart the blood enters the arteries and is carried by them to the lungs and digestive system, to be oxygenated and enriched again before returning to the capillaries.
The body’s largest blood vessels, the aorta and the pulmonary artery, are about an inch in diameter. Arteries have thick elastic walls, the pulsations, of which assist the heart in pumping. Vein walls are more rigid. Many of them, particulary in the lower part of the body, have valves which prevent a backflow of blood.
Text C. The Cardiac Rhythm
One knows that during the diastole the atria and ventricles take in (принимают) the blood. It has been determined that during the systole the atria and the ventricles discharge out the blood. The diastole of the ventricles takes place during the systole of the atria, and the systole of the ventricles takes place during the diastole of the, atria. These functions of the atria and the ventricles compose the cardiac rhythm.
The cardiac cycle lasts 0.9 second. The contraction of the atria lasts 0.2" and that of the ventricles 0.3". When the atria contract the ventricles are at rest. The diastole or the period of rest of the cardiac muscle lasts 0.4".
So during one cardiac cycle the ventricles work 0.3" but rest 0.6". The period of contraction of the ventricles is longer than that of the atria and the systolic blood pressure is always Higher than the diastolic one. Such an interesting cardiac rhythm which enables the heart to rest longer than to work is very important for the blood circulation.
If the period of cardiac rest has become constantly shorter, the rate of heartbeat increases. Such an increased rate of heartbeat may affect [a’fekt] (поражает) the heart and produce different cardiac diseases.
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