L5-U3-P2 The circulatory system

A flow chart, like this one, shows how a process begins and ends, and the steps in between.流程图，像这个 展示了一个过程怎样开始，结束和中间的步骤

The process can be of almost any kind, from manufacturing a tire to creating an advertisement.这个过程几乎可以任何形式，从制造一个轮胎到创建一个广告

Therefore, learning how to describe and explain a process in English is important.因此，学习怎么用英语描述和解释一个过程是很重要的

It's important for teachers, engineers, and people who provide customer support.这对老师，工程师，提供客户支持的人来说是很重要的

One process that we are all familiar with is our body's circulatory system.我们都熟悉的一个过程是我们的身体循环系统

This system provides oxygen throughout the body and eliminates carbon dioxide, which is a waste product.这个系统提供氧气遍及全身和排除二氧化碳，这是一种废物

If something goes wrong with this system, we need to repair it quickly, or we die.如果这个系统出错了，我们需要快速修理否则我们会死的

So it's important to understand it and keep it functioning properly.因此理解它并且让它正确工作是很重要的

（It provides oxygen to the body and eliminates carbon dioxide.）

First, the most important requirement for the system to work is a supply of air.首先这个系统工作最重要的需求是提供空气

Without fresh air with sufficient oxygen, the process won't keep us healthy and alive.没有新鲜的空气和充足的氧气，这个过程不会让我们健康和活着

So the process begins by breathing in air, which happens when the lungs expand and draw in air.所以这个过程通过吸入空气开始，当肺部扩张吸入空气时发生

Once inside the lungs, oxygen in the air is exchanged for carbon dioxide in the blood.一旦进入肺部，空气中的氧气在血液内被二氧化碳交换

This exchange happens when blood cells release carbon dioxide and absorb oxygen.当血细胞释放二氧化碳并吸收氧气时这个交换发生

This blood is now oxygenated blood, which means it carries oxygen.这血液现在是含氧血，意思是它携带氧气

To summarize, the process begins by inhaling air and oxygenating the blood.总结一下，这个过程通过吸入空气并给血液充氧开始

The oxygenated blood in the lungs then flows back to the heart.肺里含氧的血回流到心脏

The Co2 which came from the blood is exhaled, and the next cycle begins.来自血液里的二氧化碳被呼出，下个循环开始

Note that the blood in the lungs flows in a loop from the heart.记住肺部的血液从心脏循环流动

The blood which enters the loop from the heart carries carbon dioxide.从心脏进入循环的血液携带二氧化碳

Once the carbon dioxide is exchanged for oxygen, the blood continues through the loop and exits into the heart.一旦二氧化碳被转化为氧气，血液就会继续循环并进入心脏

The oxygenated blood is then pumped to the rest of the body.含氧的血液被泵到身体其它部位

（Inside the lungs, oxygen is exchanged for carbon dioxide.）

（The system won't work without a supply of air.）

（From the heart，it is pumped to the rest of the body.）