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肺についての基本知識が わずか３分で理解できる、よくできた短編教材。
医学用語がありますが､ 日本語では中学理科で習う内容。 アニメが助け。

易　　03分・・165wpm　　2015/01/26 新出　　

字幕：上の動画は開始後 で英語On/Off｡ 日本語選択､文字ｻｲｽﾞはｵﾌﾟｼｮﾝから｡
.　　　　　　　 （YouTubeは 日本語On/Off。 英語選択｡）

★下記英文はマウスオーバー辞書が使えます｡　　　　　　　 　　　　

Many of us have hundreds of things on our minds at any moment, often struggling to keep track of everything we need to do. But fortunately, there's one important thing we don't have to worry about remembering: breathing.

When you breathe, you transport oxygen to the body's cells to keep them working and clear your system of the carbon dioxide that this work generates. Breathing, in other words, keeps the body alive. So, how do we accomplish this crucial and complex task without even thinking about it?

The answer lies in our body's respiratory system（呼吸器系 réspәrәtɔri ）. Like any machinery, it consists of specialized components, and requires a trigger to start functioning. Here, the components are the structures and tissues making up the lungs, as well as the various other respiratory organs connected to them. And to get this machine moving, we need the autonomic nervous system(自律神経系 ɔ̀:tәnάmik), our brain's unconscious control center for the vital functions.

As the body prepares to take in oxygen-rich air, this system sends a signal to the muscles around your lungs, flattening the diaphragm（横隔膜）and contracting the intercostal muscles（肋間筋肉）between your ribs to create more space for the lungs to expand. Air then wooshes（ｼｭｰと動く） into your nose and mouth, through your trachea（気管 tréikiә）, and into the bronchi（気管支 複数形 brάŋkɑi） that split at the trachea's base, with one entering each lung.

Like tree branches, these small tubes divide into thousands of tinier passages called bronchioles（細気管支 brάŋkiәul）. It's tempting to think of the lungs as huge balloons, but instead of being hollow, they're actually spongy inside, with the bronchioles running throughout the parenchyma tissue（実質組織 pəréŋkәmә）.
　　（肺胞の空気に接している部分を実質といい、それ以外のところを間質と言う）

At the end of each bronchiole is a little air sack called an alveolus（肺胞 ælví:әlәs ）, wrapped in capillaries（毛細血管 複数 kǽpәlèriz）, the hemoglobin full of red blood cells containing special proteins called hemoglobin（ﾍﾓｸﾞﾛﾋﾞﾝ hí:mәglòubin）. The air you've breathed in fills these sacks, causing the lungs to inflate. Here is where the vital exchange occurs. At this point, the capillaries are packed with carbon dioxide, and the air sacks are full of oxygen.
　　（hemoglobin ： [hí：mәglòubin] 発音注意　ヘモグロビン）　
　　（赤血球の中にあるタンパク質で、酸素分子と結合し 酸素を全身に運ぶ｡）

But due to the basic process of diffusion（拡散）, the molecules of each gas want to move to a place where there's a lower concentration of their kind. So as oxygen crosses over to the capillaries, the hemoglobin grabs it up, while the carbon dixoide is unloaded into the lungs.

The oxygen-rich hemoglobin is then transported throughout the body via the bloodstream. But what do our lungs do with all that carbon dioxide? Exhale it, of course. The autonomic nervous system kicks in again, causing the diaphragm to ball up, and the intercostal muscles to relax, making the chest cavities smaller and forcing the lungs to compress. The carbon dioxide-rich air is expelled, and the cycle begins again.

So that's how these spongy organs keep our bodies efficiently supplied with air. Lungs inhale and exhale between 15 and 25 times a minute, which amounts to an incredible 10,000 liters of air each day. That's a lot of work, but don't sweat it. Your lungs and your autonomic nervous system have got it covered.