Respiratory   system                                                                                       
呼吸系统       
                                                                                                      
To understand the process of breathing         
理解呼吸的过程

In humans, the main organs responsible for respiration are present in the thoracic cavity. In the thorax region, the rib cage, and a dome shaped fibrous tissue known as the diaphragm are observed. Present within the ribcage are the pleural membranes, which enclose the lungs.
对人类而言，负责呼吸的主要器官位于胸腔。在胸部，可见胸廓，以及被称为膈的圆顶形的纤维组织。位于胸廓内的是胸膜，胸膜将肺密封起来。
The right lung is divided into three lobes- the right superior, right middle and the right inferior lobe. The left lung is smaller and has only two lobes- the left superior and the left inferior lobe. 
右肺被分隔为三叶，分别是右上叶，右中叶和右下叶。左肺较右肺小，仅有两叶，分别是左上叶和左下叶。
 Both the lungs are associated externally with small, tubular bronchi which unite and extend into the trachea. The trachea has incomplete, C-shaped rings of cartilage, which prevent the tracheal wall from collapsing. The trachea leads into the pharynx, which is connected to the nostrils. As we breathe in air, the oxygen molecules enter the nostrils and travel downwards, through the pharynx, and trachea, to finally reach the bronchi. From each bronchus, oxygen travels into the lungs. Within the lungs, the bronchus divides repeatedly to form bronchioles. Oxygen travels through these bronchioles, and reaches the alveoli; each of which is surrounded by a network of capillaries.
两侧的肺都向外与小的，管状的支气管相连，这些支气管连结并最终延伸入气管内。气管具有不完全的，C形的软骨环，这些软骨环能够防止气管壁塌陷。气管延伸至咽部，藉此与鼻孔相连。由于我们是吸入空气的，氧分子进入到鼻孔内，并继而向下扩散，穿过咽部，以及气管，最终到达支气管内。从每一个支气管处，氧分子进入到肺内。在肺内，支气管重复地分开，形成细支气管。氧经过这些细支气管，到达肺泡内；每一个肺泡的周围都包绕着毛细血管网。
A section of one alveolus shows the presence of numerous alveolar chambers with pores. Blood containing RBCs is seen flowing through the capillaries. The oxygen molecules from the alveolus diffuse into the capillary, and then get absorbed by the bluish purple RBCs. This causes oxygenation of the RBCs, and a transition in their colour from bluish purple to red is observed. The blood moving into the alveolus contains RBCs and carbon dioxide molecules. These molecules are released into the alveolus. The carbon dioxide collects in the alveolar chamber and then from the alveolus it travels through the bronchioles, into the bronchus which finally reaches the trachea and it breathed out through the nostrils.
在一个肺泡的截面内，可见大量的带有细孔的肺泡腔。含有红细胞的血液流过毛细血管。来自肺泡内的氧分子扩散入毛细血管内，并继而为带蓝色的紫色红细胞所吸收。这引起了红细胞的氧合作用，可见红细胞的颜色由带蓝色的紫色转变为红色。进入到肺泡的的血液含有红细胞和二氧化碳分子。这些分子被释放入肺泡内。二氧化碳聚集在肺泡腔内，接着从肺泡内，通过细支气管，进入到支气管内，并最终到达气管内，经由鼻孔呼出。
So the process of breathing in air rich in oxygen is called inhalation. During this process the alveoli inflate like balloons, thus the lungs expand and the muscular diaphragm moves down. During exhalation, the diaphragm moves up and the lungs contract, thus the alveoli deflate causing the air to be forced out.  This exhaled air is rich in carbon dioxide. This process of inhalation and exhalation is known as respiration, which is approximately 20 times per minute.
所以，吸入富含氧的空气的过程，被称为吸气。在这个过程中，肺泡像气球一样充气，这样，肺舒张，肌性横膈向下移动。在呼气过程中，膈向上移动，肺收缩，这样，肺泡就放气，使得气体被挤出肺泡。呼出的气体中富含二氧化碳。这个吸气和呼气的过程就称为呼吸，每分钟大约进行20次。

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