Passages through which air enters the lungs?

Air enters the lungs through the trachea, also known as the windpipe. The trachea branches into two bronchi, each of which enters one of the lungs. Within the lungs, the bronchi divide further into smaller branches called bronchioles, which end in tiny sacs called alveoli. The alveoli are where gas exchange occurs, with oxygen from the air passing into the bloodstream and carbon dioxide from the bloodstream passing into the air.