H u m a n   B o d y  - R e s p i r a t o r y  S y s t e m 

 Respiratory System
The respiratory system handles breathing. The main organ of this system is your lungs. The lungs expand to take in air "inhale" and contract to force air out "exhale".  The muscle that causes the lungs to expand and contract is called the diaphragm.  The respiratory system works very closely with the circulatory system. Tiny capillaries carry blood into the lungs and the blood takes oxygen from the lungs and gives carbon dioxide to the lungs. We exhale to get rid of the carbon dioxide and we inhale to get fresh oxygen.  
These two systems work together so closely that scientist sometimes refer to them as
one system called the cardiopulmonary system. Cardio is for the heart and pulmonary for the lungs.