THE RESPIRATORY SYSTEM Respiration

THE RESPIRATORY SYSTEM

Respiration occurs in all living things, both plants and animals. Proper functioning of this system is perhaps the single most important factor 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.
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.
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 called 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.
Mechanisms in the upper respiratory 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 called mucus, which has been produced by mucous cells lining 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.
Other structures 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, which is a double-walled membrane surrounding the lungs.
The diaphragm contracts and flattens, contributing to the extension of the vertical diameter of the thoracic cavity and raising the ribs. 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.