The Lungs are in the Thorax (top part of your body)
The thorax is separated from the abdomen by the diaphram
The air that is breathed in goes through the trachea- this splits in two and become bronchi- one 'bronchus' going into each lung.
These bronchi split again into smaller tubes called bronchioles.
This is finally ended by small bag structures called alveoli where gas exchange takes place
1- The intercostal muslces contract
2- The thorax volume increases
3- This decreases the pressure