1. What is the respiratory system?
Lesson 16
What is the respiratory system?

2. Almost every living thing must take in oxygen in order to live
Almost every living thing must take in oxygen in order to live. Breathing is the process of bringing air into the organism.
Breathing also gets rid of used air.

3. As you have learned, breathing is done by means of lungs
As you have learned, breathing is done by means of lungs. The lungs, along with several other organs, make up the respiratory system.
The job of the respiratory system is to take oxygen into the lungs and to get rid of carbon dioxide and water.

4. Here is the path air takes when you inhale or exhale:
1- Air enters the body through the mouth or nose
2. It moves into your throat and passes through the windpipe, or trachea.

5. 3- The trachea branches into two tubes called bronchi
3- The trachea branches into two tubes called bronchi. Each bronchus extends into one of the lungs.

6. 4- The lungs are the main organs of the respiratory system
4- The lungs are the main organs of the respiratory system. In the lungs, the bronchi branch into smaller and smaller tubes.
At the end of the smallest tubes are tiny air sacs called alveoli. Each lung contains millions of air sacs.

7. Each air sac is surrounded by capillaries.
While the air is in the air sacs, two things happen:
1. Blood picks up oxygen
2. At the same time, the air sacs take the carbon dioxide from the blood.

8. When you exhale, you breathe out the carbon dioxide
When you exhale, you breathe out the carbon dioxide. Some waste water and heat are also exhaled.