Caption

Respiratory system. Artwork of a child's healthy respiratory system. Air is breathed in through the nose or mouth (upper left). It travels down the trachea (blue, ringed with cartilage) and into the two bronchi that branch into the many smaller bronchi of the two lungs (pink, lower left & right). Finally the air travels along tiny bronchioles, ending up at air sacs called alveoli (not seen) where gas exchange with the blood takes place. Waste gases are expelled by the opposite route. The motion of gas into and out of the lungs is controlled by movement of the diaphragm, the sheet of muscle under the lungs, and the ribcage.