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Every time you breathe in, air travels down the trachea, through a series of channels called bronchi, and finally reaches little clusters of air sacs called alveoli.
每次当你呼吸时，空气将进入气管，经过一些名为支气管的通道，最后到达一些小的气囊团，叫做肺泡。
There are some 600 million alveoli in the lungs, adding up to a surface area of roughly 75 square meters -- the size of a tennis court.
肺里有将近6亿个肺泡，总面积大约为75平方米--面积和一个网球场差不多大。
These tiny sacs, only one cell thick, facilitate a crucial exchange: allowing oxygen from the air we breathe into the bloodstream and clearing out carbon dioxide.
这些只有一个细胞厚的小气囊促成了一项非常关键的转换：使氧气能成功的进入到血管里，并清理掉二氧化碳。
Pneumonia wreaks havoc on this exchange. Pneumonia is an infection of the alveoli that causes them to fill with fluid.
肺炎破坏了这个环节。肺炎是一种肺泡感染，会导致肺泡充满液体。
There are many different kinds of pathogens that can cause pneumonia. The most common ones are viruses or bacteria.
肺炎可以有许多不同的病因，最常见的是病毒或病菌。
These microscopic invaders enter the body via droplets either in the air we breathe, or when we touch our eyes, noses, or mouths after touching a contaminated surface.
这些微小的入侵者要么是通过吸入的空气中的水气，要么是在我们碰过被感染的平面后，又接触了我们的眼睛、鼻子，或嘴而进入我们体内。
Then, they face the respiratory tract's first line defense: the mucociliary escalator.
然后它们会面对呼吸道的第一道防线：粘膜纤毛自动扶梯。
The mucociliary escalator consists of mucus that traps invaders and tiny hairs called cilia that carry the mucus toward the mouth, where it can be coughed out.
粘膜纤毛自动扶梯由困住入侵者的粘液和一些细小的毛发组成，这些毛发叫做纤毛，负责把粘液运送至嘴巴，使它们可以被咳出去。
But some of these invaders may get past the mucociliary escalator into the lungs, where they meet the alveoli.
但是有些入侵者有可能通过粘膜纤毛自动扶梯并进入到肺里，并接触到肺泡。
Because alveoli serve as critical exchange points between the blood and air from the outside world,
因为肺泡相当于血液和来自体外的空气之间的一个临界交换点，
they have their own specialized types of white blood cells, or macrophages, which defend against foreign organisms by enveloping and eating them.
它们拥有专门的白血细胞，又名巨噬细胞，这种细胞通过包络和吞噬外来细胞来进行防御。
When pathogens enter the lungs, the macrophages work to destroy them. The immune system releases additional white blood cells in the alveoli to help.
当病因抵达肺部时，巨噬细胞就会开始摧毁它们。免疫系统也会在肺泡中释放出更多的白血细胞去帮忙。
As these immune cells fight the pathogens, they generate inflammation -- and fluid as a by-product of the inflammation.
当免疫细胞和病因搏斗时，它们会制造一些炎症--还有作为副产品的液体。
When this fluid builds up, it makes gas exchange inside the alveoli much more difficult.
当这些液体积聚起来后，就会使肺泡内的空气转换更加困难。
As the level of carbon dioxide in the bloodstream begins to rise, the body breathes more quickly to try to clear it out and get more oxygen in.
当血液里的二氧化碳含量增加时，身体会更快的呼吸，试图把它们清除掉并且吸进更多氧气。
This rapid breathing is one of the most common symptoms of pneumonia.
急促的呼吸是肺炎的一种很常见的现象。
The body also tries to force the fluid out of the alveoli through coughing.
身体也试图通过咳嗽，使那些液体脱离肺泡。
Determining the cause of pneumonia can be difficult, but once it is established, doctors can prescribe antibiotics, which may include either antibacterial or antiviral treatments.
确定肺炎的源头可能会有些困难，但是当它发生了，医生就可以开抗生素，含有抗菌或抗病毒的治疗。
Treatment with antibiotics helps the body get the infection under control.
抗生素的治疗能够使身体内的炎症得到控制。
As the pathogen is cleared out, the body gradually expels or absorbs fluid and dead cells.
当病因清除以后，身体会缓慢的驱逐或吸收液体和死去的细胞残骸。
The worst symptoms typically fade out in about a week, though full recovery may take as long as a month.
最极端的症状也会在一星期内消失，但是完全康复可能需要长达一整个月。
Otherwise healthy adults can often manage pneumonia at home.
除此以外，健康的成年人在家里就能够使肺炎得到控制。
But for some groups, pneumonia can be a lot more severe,
但是对一些群体来说，肺炎的后果则要严重得多，
requiring hospitalization and oxygen, artificial ventilation, or other supportive measures while the body fights the infection.
当身体抗击炎症时，需要住院治疗和氧气、人工呼吸机，或是其它辅助措施。
Smoking damages the cilia, making them less able to clear even the normal amount of mucus and secretions, let alone the increased volume associated with pneumonia.
吸烟会对纤毛造成损伤，使他们难以清除正常含量的粘液和分泌物，更何况是由肺炎引起的超标含量。
Genetic and autoimmune disorders can make someone more susceptible to pathogens that can cause pneumonia.
遗传和自身免疫的毛病可以使一些人更加容易感染肺炎。
Young children and the elderly also have impaired clearance and weaker immune systems.
幼童和老年人肺部的自我清除能力和免疫系统都相对较弱。
And if someone has viral pneumonia, their risk of bacterial respiratory infection is higher.
当一个人患有肺炎时，它们患有细菌性呼吸感染的风险也更高。
Many of the deaths from pneumonia are due to lack of access to healthcare.
许多因肺炎死亡的案例都是由于没有很好的医疗条件导致的。
But sometimes, even with appropriate care, the body enters a sustained fight against the infection it can't maintain,
但是有些时候，即使有需要的设施和看护，当身体进入了一场自身无法承受的对抗感染的持久战，
activating inflammatory pathways throughout the body, not just in the lungs.
就会激活身体各处的炎症途径，不只是在肺里。
This is actually a protective mechanism, but after too long in this state organs start shutting down, causing shock and sometimes death.
这其实是一个保护机制，但是这个状态过久，器官就会开始衰竭，引发休克，甚至是死亡。
So how can we prevent pneumonia? Eating well and getting enough sleep and exercise helps your body fight off infections.
那么，我们要如何预防肺炎呢？正常饮食，充足的睡眠和运动能帮助你的身体战胜感染源。
Vaccines can protect against common pneumonia-causing pathogens,
疫苗可以对抗常见的肺炎病因，
while washing your hands regularly helps prevent the spread of these pathogens -- and protect those most vulnerable to severe pneumonia.
同时，勤洗手也可以抑制这些病因的传播--并保护那些对肺炎没有抵抗能力的人。
