Here's how it works:

* Inhalation: The diaphragm, a muscle below the lungs, contracts, causing the lungs to expand. This creates a lower pressure inside the lungs compared to the air outside, drawing air in through the nose and mouth.

* Exhalation: The diaphragm relaxes, causing the lungs to deflate. This increases the pressure inside the lungs, forcing air back out.

The respiratory system also includes the trachea (windpipe), bronchi, and alveoli (tiny air sacs in the lungs) which all play a role in getting oxygen to the blood.