時差N小時:人體如何造血? How Does The Body Make Blood?
如果血液不能在我們身體內(nèi)循環(huán)，為人體輸送氧氣和營養(yǎng)，我們便無法存活。
Blood is so important to life that the bodyconstantlymakes new blood.
血液對生命十分重要，所以人體會不斷的制造新鮮血液。
To do this, the body must produce the liquid partof blood, called plasma, and the cells that floatin it.
人體在造血時必須要產(chǎn)生血液的液體部分，即血漿，以及浮在血漿上的細(xì)胞。
Plasma is made mostly of water and salts that we absorb through our digestive tractseveryday.
血漿主要由我們通過消化道每天吸收的水和鹽組成。
Its job is to deliver nutrients and water throughout the body.
它的作用就是輸送水和營養(yǎng)物質(zhì)到全身各個部位。
Ninety-nine percent of the blood cells floating in plasma are red blood cells,
浮在血漿上99%的血細(xì)胞都是紅細(xì)胞，
which carry oxygen from the lungs to the rest of the body and give blood its red color.
它們會把肺部的氧氣輸送到全身各處，這樣血液才會呈現(xiàn)出紅色。
The average life of a red bloodcell is four months.
一個紅細(xì)胞的平均壽命是4個月。
What Happens after that?
接下來會發(fā)生什么呢?
The spleen continuously destroys millions of old red blood cells, recycling the iron to make newred cells.
脾臟不斷地將數(shù)百萬老化的紅細(xì)胞解體，循環(huán)利用其中的鐵元素來制造新的紅細(xì)胞。
White blood cells, which are part of the immune system, and platelets,
白細(xì)胞是人體免疫系統(tǒng)的一部分而血小板則在人體傷口處起到凝血作用，
which help with bloodclotting at a site of injury, also float in plasma.
這兩種血細(xì)胞也都漂浮在血漿上。
They have much shorter life spans than red cellsand also are replaced continuously.
但是它們的存活周期要比紅細(xì)胞短，同時也會被不斷地更新。
If you've ever seen a bone cut crosswise, with soft tissue called marrow inside, then you'veseenwhere blood cells are made.
如果你看到過一塊被橫切的骨頭，你就會看到里面的軟組織，即骨髓，它是專門制造血細(xì)胞的。
Bone marrow contains special blood cells,
骨髓含有特殊的血細(xì)胞，
which constantly divide toproduce new cells to replace the ones that have been destroyed.
這種細(xì)胞會不斷分離產(chǎn)生新的細(xì)胞來取代那 些已被破壞的細(xì)胞。
Why all this bloody business inthe bone marrow?
為什么所有的造血工作都在骨髓中進(jìn)行呢?
The body's process of forming new blood cells helps you recover if you loseblood to an injury,
答案是如果你因受傷而流血的話，人體生成新血細(xì)胞的過程便能幫助你復(fù)原，
and it also helps blood perform its many functions despite cell damage and loss.
同時，盡管存在細(xì)胞受 損或缺失，這個過程也能幫助血液發(fā)揮很多其它的功能。
