英语听力文摘 English Digest 617、人体如何造血？

 　　If blood didn’t circulate through our bodies, carrying oxygen and nutrients¹, we wouldn’t be able to live. Blood is so important to life that the body constantly makes new blood.

 

　　To do this, the body must produce the liquid part of blood, called plasma², and the cells that float in it. Plasma is made mostly of water and salts that we absorb through our digestive tracts³ every day. Its job is to deliver nutrients and water throughout the body.

 

　　Ninety-nine percent of the blood cells floating in plasma are red blood cells, which carry oxygen from the lungs to the rest of the body and give blood its red color. The average life of a red blood cell is four months.

　　What Happens After That?

 

　　The spleen continuously destroys millions of old red blood cells, recycling the iron to make new red cells. White blood cells, which are part of the immune system, and platelets, which help with blood clotting⁴ at a site of injury, also float in plasma. They have much shorter life spans than red cells and also are replaced continuously.

 

　　If you’ve ever seen a bone cut crosswise, with soft tissue called marrow⁵ inside, then you’ve seen where blood cells are made. Bone marrow contains special blood cells, which constantly divide to produce new cells to replace the ones that have been destroyed. Why all this bloody⁶ business in the bone marrow? The body’s process of forming new blood cells helps you recover if you lose blood to an injury, and it also helps blood perform its many functions despite cell damage and loss.

1 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

2 plasma   

n.血浆，细胞质，乳清

参考例句：

• Keep some blood plasma back for the serious cases.留一些血浆给重病号。
• The plasma is the liquid portion of blood that is free of cells .血浆是血液的液体部分，不包含各种细胞。

3 tracts   

大片土地( tract的名词复数 )； 地带； （体内的）道； （尤指宣扬宗教、伦理或政治的）短文

参考例句：

• vast tracts of forest 大片大片的森林
• There are tracts of desert in Australia. 澳大利亚有大片沙漠。

4 clotting   

v.凝固( clot的现在分词 )；烧结

参考例句：

• The study was also based only on the one anti-clotting drug. 所用抗血栓药物也仅限于一种。 来自互联网
• A plasma protein that is converted into thrombin during blood clotting. 凝血原酶一种血浆蛋白质，在血液凝聚时转化成凝血''。'酵'。''''。'素'。''。 来自互联网

5 marrow   

n.骨髓；精华；活力

参考例句：

• It was so cold that he felt frozen to the marrow. 天气太冷了，他感到寒冷刺骨。
• He was tired to the marrow of his bones.他真是累得筋疲力尽了。

6 bloody   

adj.非常的的；流血的；残忍的；adv.很；vt.血染

参考例句：

• He got a bloody nose in the fight.他在打斗中被打得鼻子流血。
• He is a bloody fool.他是一个十足的笨蛋。