Text АThe respiratory system
1 Respiration occurs in all living things, both plants and animals.The proper function of this system is perhaps the most important one in the sustaining of life. Interruption of breathing for only a few minutes by suffocation or strangulation causes death. In the human organism, respiration consists of those processes by which the body cells and tissues make use of oxygen and by which carbon dioxide or the waste products of respiration are removed.
2 Inhaled air contains about 20 per cent oxygen and four hundredths of one per cent carbon dioxide. Exhaled air consists of approximately 16 per cent oxygen and 4 per cent carbon dioxide. Nitrogen, which makes up about 79 per cent of the atmosphere, is not involved in the breathing process. When air is inhaled into the lungs, a portion of the oxygen is passing into the blood and is being circulated through the body. At the same time, carbon dioxide is being diffused out of the blood into the lungs and exhaled.
3 Air is breathed through either the mouth' or nose into the oral cavity, or pharynx. It then passes through the voice box, or larynx, into the windpipe, or trachea. The trachea ultimately divides into two smaller tubes, bronchi, one is going to each lung. The bronchi divide into tiny passage-ways that are named bronchioles, which lead directly to minute air sacs, or alveoli. The exchange of life-giving gases is effected through the walls of the alveoli.One must know that mechanisms in the 'upper res’piratory tract 'serve to 'filter, and 'warm the 'air in its 'journey to the lungs. The 'hairs, or 'cilia, in the nostrils partially 'filter out 'dust particles as does 'sticky secretion, 'mucus, which has been produced by 'mucous cells. It lines the mouth, 'nasal passages, pharynx and trachea. Cilia in the 'nasal 'passages and trachea are effective in helping to remove 'foreign particles from the 'upper respiratory tract.
4 Other structures which have been connected with the system include: the laryngeal tonsils, which are masses of tissue in the nasopharynx or posterior portions of the nasal passages (adenoids are infected or diseased laryngeal tonsils); the sinuses, cavities in the bones in the front part of the skull that provide resonance to the voice, and the pleura, a double-walled membrane which surrounds the lungs.
5 When the diaphragm contractsand flattens, it contributes to the extension of the vertical diameter of the thoracic cavity. Air is constantly renewing in the lungs. The capacity of the air passages is increasing. Any muscular effort, e.g. even standing up, increases the number of respirations.
Текст А дыхательной системы
The term «respiration» means the exchange of gases (oxygen and carbon dioxide) which takes place between the living organism and the environment. One must consider that in higher organisms this exchange takes place at several different levels. An initial exchange must occur between the air in the lungs, from which the oxygen is being continually taken up and into which carbon dioxide is being continually poured, and the external air. This is the process of external respiration.
The composition of the air inside the lungs is different from that of the air which we inhale. The content of alveolar air is very constant, especially the one of carbon dioxide, the partial pressure of which is normally 40 mm of mercury. This constancy is the result of a self-regulating mechanism by which the respiratory activity is governed by the amount of carbon dioxide which has been eliminated from the organism.
The exchange of gases varies according to the size and activity of the organism. In man at rest the absorption of oxygen reaches about 0.25 litre a minute and the elimination of carbon dioxide 0.2 litre. At a time of maximum muscular activity, the consumption of oxygen and the production of carbon dioxide may both exceed 4 litres a minute.
The movement of air into the lungs is brought about by an increase in the volume of the thoracic cavity with the action of the respiratory muscles. The lungs follow this movement passively. Some of the inspiratory muscles have a fixed point on the ribs; when the ribs are being raised the muscles increase the anteroposterior and transverse diameters of the thoracic cavity (costal respiration). Another important muscle is the diaphragm, a thin dome-shaped «sheet», which closes the lower part of the thorax and separates it from the abdomen. The diaphragm contracts and flattens; it contributes in this way to the extension of the vertical diameter of the thoracic cavity and raises the ribs (abdominal respiration). At the time of expiration, the thorax returns to its initial
position, and air is expelled through the same tracts that had been used by fresh air during inspiration.
In an individual at rest the number of inspirations per minute is 10 to 15; the pulmonary ventilation, or the volume of air which passes through the respiratory system each minute, is about 6litres per minute. During intense muscular activity the inspiration rate may rise to 50 and the ventilation to 150 litres or more per minute.
Дыхание текст В
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