The Respiratory System

In our last lesson, you learned that the circulatory system begins when you take a breath of air. You learned how oxygen in that air is mixed with blood that's been pumped to your lungs. And you also learned how blood delivers oxygen to your cells and helps get rid of unwanted waste and carbon dioxide. 

Without oxygen, your cells would die -- and so would you. This means that your circulatory and respiratory systems must work together. 

This lesson is about your respiratory system -- which also begins with breathing.