The Respiratory System

The respiratory system consists of the lungs and those passageways which conduct air to and from the lungs. The conducting airways, external to the lungs, are the nose, pharynx, larynx, trachea and the extrapulmonary bronchi. The left and right nasal cavities are separated by the nasal septum and contain the superior, middle and inferior nasal conchae which are covered with mucous membrane. The nasal cavities are connected to paranasal sinuses in the frontal, ethmoid, sphenoid and maxillary bones. Collectively, the nasal cavities and paranasal sinuses warm, humidify and filter the inhaled air. The auditory tubes (Eustachian tubes) from the middle ears enter the nasopharynx, the junction of the posterior nasal cavities and the pharynx. The pharynx divides into the esophagus and the larynx. The entrance to the larynx is protected by the epiglottis, a leaf-like flap which folds down over the entrance to the larynx during swallowing to prevent food from entering the lungs. The larynx is surrounded by a cartilaginous skeleton which protects the glottis and provides an anchor for muscles involved in swallowing and speech. Beneath the larynx, the trachea extends to the bronchi. The trachea is surrounded by incomplete rings of cartilage which provide some flexibility, but which also prevent the collapse of the trachea under external pressure.

The trachea divide into left and right primary bronchi, which enter the lungs at the hilus. The right primary bronchus has a relatively vertical alignment and divides into three secondary bronchi, one to each of the upper, middle and lower lobes of the right lung. The left primary bronchus travels more horizontally, and divides into two secondary bronchi, one to each of the upper and lower lobes of the left lung. The secondary bronchi divide into tertiary bronchi which, in turn, give rise to the smaller bronchioles. The bronchioles undergo up to 17 generations of division before giving rise to the respiratory bronchioles, respiratory ducts, alveolar ducts and, thence, the alveolar sacs and individual alveoli. The exchange of gases between the air and the bloodstream occurs overwhelmingly in the alveoli.

The lungs are surrounded by a double-walled membrane, the pleura. The outer layer, the parietal pleura, is connected to the inside of the thoracic body wall, that is to say the diaphragm and the inside of the rib cage. The inner layer, the visceral pleura, is connected to the surface of the lungs. During inspiration, the expansion of the rib cage and the fall of the diaphragm pulls on the parietal pleura and creates a partial vacuum in the interpleural space. This in turn pulls on the visceral pleura and so expands the lungs. As the lungs expand, the pressure within the alveoli drops, drawing air into the lungs. During expiration, relaxation of the diaphragm and the intercostal muscles causes a passive contraction of the thoracic cavity, driving air out of the lungs. During normal ventilation, the pressure gradient between the alveoli and the atmosphere is extremely small, so that ventilation is normally a very energy-conservative process. Small changes in airway resistance, as in asthma, or lung elasticity, as in emphysema, can therefore create physiologically significant increases in the work of ventilation.


English - French Lexicon

auditory tube: trompe auditive ;alveolar duct: canal alvéolaire ;alveolar sac: sac alvéolaire ;alveolus: alvéole ;bronchiole: bronchiole ;bronchus: bronche ;diaphragm: diaphragme ;epiglottis: épiglotte ;glottis: glotte ;hilus: hile ;larynx: larynx ;lung: poumon ;nasal cavity: rhinopharynx ;nasal septum: cloison du nez ;nose: nez ;nostril: narine ;pharynx: pharynx ;pleura: plèvre ;trachea: trachée ;turbinate: cornet du nez

English - Japanese Lexicon

auditory tube: 耳管 (jikan); alveolar duct: 肺胞道 (haihoudou); alveolar sac: 肺胞嚢 (haihounou); alveolus: 肺胞 (haihou); bronchiole: 細気管支 (saikikanshi); bronchus: 気管支 (kikanshi); diaphragm: 横隔膜(oukakumaku); epiglottis: 侯頭蓋 (koutougai); expiration: 呼気(koki); glottis: 喉頭口 (koutougou); hilus: 肺門 (haimon); inspiration: 吸気 (kyuuki); larynx: 喉頭 (koutou); lobe: 肺葉 (haiyou); lung: (hai); nasal cavity: 鼻腔 (bikou); nasal septum: 鼻中隔 (bichuukaku); nose: (hana); nostril: 鼻孔 (bikou) paranasal sinus: 副鼻腔 (fukubikou); pharynx: 咽頭 (intou); pleura: 胸膜 (kyoumaku); trachea: 気管 (kikan); turbinate: 鼻甲介 (bikoukai)