Английские тексты из учебника Масловой
.docText A. Sechenov and His Works on the Blood Gases
-------------------------------------------------
I. M. Sechenov was a prominent Russian scientist, the founder of Russian physiology and scientific psychology.
The range of Sechenov's scientific interests and the number of his research works are really great. 106 scientific works were written by him. In these works he included the findings which he had observed and determined before.
Some of his research works were connected with the investigation of the blood gases and their role in the respiratory process.
I. M. Sechenov isolated the blood gases and found out that most of the blood gases were combined with erythrocytes. No physiologist had been able to do it before Sechenov. On the basis of his observations I. M. Sechenov came to the conclusion that hemoglobin was that substance of the blood which accomplished the exchange of oxygen and carbon dioxide in the respiratory process. Physiologists of many countries who had worked on this problem before Sechenov could not estimate the role of hemoglobin in the act of respiration. So the accomplishment of the respiratory process is due to hemoglobin.
I. M. Sechenov investigated the process of absorption of carbon dioxide by the solutions of salts. When he had completed his investigations, he proved that only 2/3 of carbon dioxide were dissolved in plasma. The rest of carbon dioxide was combined with red blood cells. The transfer of carbon dioxide from the blood into the lungs was due to the law of diffusion of gas from fluid into the air. When Sechenov had investigated this phenomenon, he was able to answer the question why oxygen passed into the blood from atmospheric gases during the act of respiration.
Text B. The Exchange of Gases in the Lungs
------------------------------------------
The exchange of gases takes place in the alveoli of the lungs. Oxygen passes into the blood and carbon dioxide passes into the atmospheric air.
The exchange of oxygen and carbon dioxide is due to the difference of partial pressure of these gases in the alveolar air and in the venous blood.
The partial pressure of oxygen in the alveolar air is higher than in the venous blood. The transfer of oxygen from the atmospheric air into the blood is due to this difference of pressures.
The partial pressure of carbon dioxide is higher in the venous blood and this enables carbon dioxide to pass from the blood into alveolar air.
The process of transfer of gases into the medium with a lower partial pressure is called diffusion. Hemoglobin is that substance of the blood, which transfers oxygen in the blood. The oxygen capacity of the blood averages to 18-20 ml per 100 g of blood. Carbon dioxide is transferred in combination with hemoglobin and as bicarbonic salts.
The combination of oxygen and hemoglobin is called oxyhemoglobin, that of carbon dioxide and hemoglobin - carbohemoglobin.
Text C. The Physiology of the Lungs
-----------------------------------
The physiology of the lungs is associated with their structure. There are over 700,000,000 alveoli in the lungs. The total surface of the alveoli is about 90 square meters. The lungs have many capillaries with the total surface of about 80 sq. m. This particular structure of the lungs enables the exchange of gases between the alveolar air and the blood.
Elastic fibers of connective tissue composing the walls of the alveoli, alveolar passages and the visceral pleura enable the lungs to dilate.
When one breathes normally not all the alveoli and capillaries of the lungs are opened. When respiration becomes deep, the number of the opened alveoli and capillaries increases. The flow of blood into the lungs increases when one breathes in and it decreases when one breathes out.
The regulation of the vital capacity of the lungs is of particular importance to the exchange of oxygen and carbon dioxide taking place in the lungs. It is considered that in the adult the vital capacity of the lungs is about 3-4 liters. When the depth of respiration increases the vital capacity may be 6 liters and even more.
The lungs take part in the production of physiologically active substances, in the regulation of blood coagulation, in the metabolism of proteins, fats and carbohydrates.
Text D
------
If one investigates the act of inspiration one will observe such phenomena.
When one breathes in, the external intercostal muscles contract and lift the ribs. At this moment the diaphragm also contracts and goes down. The volume of the chest increases. The increase of the chest volume enables the lungs to extend. The pressure in the lungs becomes less and the atmospheric air enters the lungs.
When one breathes out, the external intercostal muscles and the muscles of the diaphragm become relaxed. The ribs go down, the diaphragm goes up, the volume of the chest decreases and the lungs contract. The pressure in the lungs becomes higher and the air goes out of the lungs. If one is sitting or lying one makes 16-20 respirations per minute. On physical exertion the respiratory rate and the depth of respiration increase.
Normally during one inspiration the man breathes in about 500 ml of air. On deep inspiration one breathes in 1.5-2 liters of air.
The vital capacity of the lungs in the male averages 3.5-4 liters and in the female - 3-3.5 liters.
The respiratory rate and its depth depend on the amount of carbon dioxide in the blood.
Text A. The Brain
-----------------
Scientists consider that our brain is the most complicated mechanism, which has ever been constructed.
The weight of the human brain is from one to two kilograms. It has a volume of about 3.21 litres and consists of about 12 billion cells. It has been determined by the scientists that each cell is connected to the other directly or indirectly by nerve fibers.
The brain is the centre of а wide system of communication. It has been found out that a constant flow of stimuli comes into the brain through the spinal cord. The stimuli come to the brain from our eyes, ears and other sense organs for pain, temperature, smell and other feelings. When all the received stimuli have been summarized and analysed the brain sends orders through the nerve fibers in the spinal cord to different parts of the human body. It is due to these orders that one eats, moves, hears, sees and does many other things.
To estimate the functions of different areas of the brain many experiments have been carried out by the investigators. It is due to such experiments that the investigators have been able to determine those areas of the brain which control vision, hearing, physical movements and even emotions.
Due to experimental studies it has been determined that the motor cortex, controlling many body movements of the human, being becomes tired rapidly. But the hypothalamus, which controls such functions as blood pressure, is almost never tired.
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 unconditioned 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.
Text С
------
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 alloy 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, the inhibited cortical cells do not react to them.
Text D
------
One of the scientific research institutes in Czechoslovakia 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 B1 and B6, produced considerable increase of white blood cells and decreased the amount of iron in the blood.