The Digestive System
消化系统 I-07 / 007

Have you ever wondered what happens to the food you eat? Most people know that food provides energy for the body. Do you know how food becomes energy? We can find out by studying the digestive system.

Digestion is the breaking down of food into nutrients. Nutrients are the parts of food that the body can use. The nutrients must be small enough so that the blood can carry them to all cells of the body.

The first part of the digestive system is the mouth. Food enters the body through the mouth. Teeth grind up the food into small pieces. The food is mixed with a liquid called saliva.

Saliva has a chemical that changes starch into sugar. This is the first step in breaking down food. When you swallow, food goes down the esophagus. This long tube leads into the stomach.

In the stomach more chemicals are mixed with the food. More starches are changed into sugar. Stomach juices begin to break down proteins. The muscles of the stomach act like a blender to turn the food into liquid.

When food leaves the stomach, it goes into the small intestine. The small intestine is like a hose. If it were stretched out, it would be 20 feet long. Blood vessels line the walls of the small intestine. These blood vessels soak up the nutrients. Then the blood carries the nutrients to every cell in the body.

The food that is left is not needed by the body. It passes into the large intestine. From there it is carried out of the body.

Words and Phrases

digestive system 消化系统

nutrient [ˈnju:trɪənt] 名 营养物

grind up 把……磨成粉末

saliva [səˈlaɪvə] 名 唾液，口水

starch [stɑ:tʃ] 名 淀粉

swallow [ˈswɒləʊ] 动 吞，咽

stomach juice 胃液

break down 分解

protein [ˈprəʊti:n] 名 蛋白质

blender [ˈblendə] 名 搅拌机

small intestine 小肠

blood vessel 血管

soak up 吸收，吸取

large intestine 大肠

Practice

1. Put these events in the order that they happened. Use 1, 2 and 3 to mark the right order.

________The food that is left goes into the large intestine.

________Chemicals mix with food in the stomach.

________Teeth grind up the food into small pieces.

2. When is food mixed with saliva?

A. while it is in the stomach

B. when it is in the mouth

C. after it is in the small intestine

3. When does food go down the esophagus?

A. after you swallow

B. after it leaves the stomach

C. when it leaves the large intestine

4. When do stomach juices begin to break down proteins?

A. when food is in the mouth

B. after food is in the small intestine

C. while food is in the stomach

5. Where do blood vessels soak up the nutrients?

A. in the small intestine

B. in the large intestine

C. in the stomach

译文

消化系统

你是否曾想过吃下去的食物到底变成了什么样子？大多数人知道食物能给身体提供能量。你知道食物是怎样转变成能量的吗？通过对消化系统的研究我们可以找到答案。

消化就是把食物分解成营养物质。食物中的营养物质为人体所需。营养物质必须足够小，血液才能把它们传输到身体的所有细胞。

消化系统的第一个部分是口腔。食物从口腔进入体内，接着牙齿把它们咀嚼成细小的物质，食物会与一种称为“唾液”的东西混合。

唾液里含有一种把淀粉转化为糖的化学物质，这是分解食物的第一步。当你吞咽食物，它们便进入食道。食道是一条通往胃的长管。

在胃里会有更多的化学物质与食物混合，更多的淀粉转化成糖。胃液开始分解蛋白质，胃部肌肉像搅拌机一样把食物转变成液体状。

当食物离开胃部，便进入小肠。小肠就如同一条软管，如果把它展开，便足足有20英尺（约6.1米）长。血管沿着小肠壁呈线状分布，这些血管吸收营养物质，然后由血液把营养物质输送到身体的各个细胞中。

剩下的食物则是身体不需要的。它们进入大肠，从那里排出体外。

练习

1．将这些事项按照发生的先后顺序进行排列，分别用1,2,3标注。

________被留下来的食物进入大肠。

________食物与化学物质在胃里混合。

_________牙齿把食物咀嚼研磨成细小的物质。

2．什么时候食物与唾液混合在一起？

A．在胃里时

B．在嘴里时

C．到小肠里后

3．什么时候食物进入食道？

A．当你吞下食物时

B．当食物离开胃时

C．当食物离开大肠时

4．什么时候胃液开始分解蛋白质？

A．当食物在口腔时

B．当食物进入小肠后

C．当食物在胃里时

5．血管在哪里吸收营养？

A．小肠里

B．大肠里

C．胃里