David C. Dugdale (2012) defines gaseous exchange as the delivery of oxygen from the alveolar air space into the pulmonary capillaries and the elimination of carbon dioxide from the capillaries to the lung. Both processes occur via diffusion, from a high concentraion to a low concentration. Capillaries are located in the walls of the alveoli and are only one cell thick, making them well adapted for gaseous exchange.
Air enters the body through the mouth or nose, it then travels to the pharynx, passing through the larynx, entering the trachea, which branches into a right and left bronchus. It sub-divides into smaller branches called bronchioles, with tiny air sacs called alveoli, which inflates during inhalation and deflates during exhalation