Your trachea and bronchi bring the air you breathe to your lungs. Each bronchus is shaped like a tree, with lots of smaller and smaller branches. The smallest branches are called bronchioles and at the end of these are your air sacs (alveoli). Alveoli are filled with air and look like bunches of grapes! There are about 600 million alveoli in your lungs and they are all covered with capillaries, which is where the oxygen gets into your blood!