How do lungs work?
When you breath in, air flows through the bronchi and bronchioles in your lungs, and comes to a halt in millions of air pockets, known as alveoli. These pockets are surrounded by blood vessels that are so tiny they can be seen only under a microscope. The blood vessels are so thin that gases can pass straight through them. As blood flows around the air pockets, oxygen passes into the blood, while carbon dioxide waste in the blood passes into the pockets to be breathed out.

Inside a lung
The trachea branches off to the right and left lung. Each lung is made up of a mass of subdividing airways.