The air we breathe goes through the nose,nasal passages, and then through the trachea or windpipe,which separates into two branches, called brochi or bronchial tubes, one entering lung. the bronchi subdivide many times inside the lungs, analogous to the branching pattern of grapes finally becoming hair like tubes called bronchioles . in the last part of the terminal bronchioles are tiny bubble like bunch of structures called alveoli or air sacs.