A series of definitions were presented: ventolation, inhalation, expiration, intercostal,and diaphragm. The mechanics of breathing involving atmospheric pressure and pleural pressure, movement of the diaphragm and ribs, increasing chest cavity and lowering pleural pressure causing external air to rush in. Expiration was presented as the opposite procedure. The brain and nerve control was presented. A few disorders of the respiratory system, asthma and pneumonia were discussed.