The lower part of the respiratory system can be described as an upside down tree in the chest. The first part, called the trachea or windpipe, is the long tube that goes from the back of the throat to the chest. From there it branches off into two bronchial tubes that extend into the right and left lungs. These bronchial tubes then branch off into smaller tubes called bronchioles , ending at alveoli , the tiny air sacs where the exchange of oxygen and carbon dioxide occurs. Depending on the condition an individual has, some parts can produce different sounds, like rhonchi, when air moves through them.