Тексты для мединститута 5 (перевод)
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Text A. Sechenov and His Works on the Blood Gases
I. M. Sechenov(1829-1905)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 (растворяются) 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 (закон) 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 ....
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 (парциальное) 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 (среда) 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 millilitres (ml) per 100 gr 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 sq. m (square metres). 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 litres. When the depth of respiration increases the vital capacity may be 6 litres 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.
If one investigates the act of inspiration (вдох) one will observe such phenomena.
When one breathes in, the external intercostal muscles contract and lift (поднимать) 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 (расслабленные). 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 litres of air.
The vital capacity of the lungs in the male averages 3.5-4 litres and in the female 3-3.5 litres.
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 kg. (kilograms). It has a volume of about 3.21 litres and consists of about 12 billion (миллиард) 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 a 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.
Tо 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.
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