Respiratory system. Computer artwork of a naked woman with a healthy respiratory system. Below the voice box (larynx, cream) the trachea (windpipe) can be seen at centre, splitting into two bronchi (one for each lung). Inside the lungs (pink) the bronchi further divide into many bronchioles (blue). Each bronchiole becomes smaller, finally ending in alveoli (tiny air sacs, green). The lungs are the site of gaseous exchange; oxygen enters the blood and carbon dioxide leaves. Also seen is the thoracic diaphragm, a sheet of muscle extending below the lungs.