Gaseous exchange refers to the movement of oxygen and carbon dioxide across the respiratory surface.Respiratory surface are specialized organs for gaseous exchange. Gaseous exchange takes place through a process of diffusion.
Gaseous exchange in mammals happens as a result of inhalation and exhalation. Inhalation is breathing in air in to the lungs as elaborate beklow:-
Exhalation is the breathing out of air from the lungs. During inhalation the muscle of the diaphragm contract pulling the diaphragm downwards. As this happens, the external inter costal muscle contract and pull the rib cage upward and outwards. This increase volume and decreases pressure in the thorax. This makes air rush in the lungs.
During exhalation the muscles of the diaphragm resumes its dome shape. The external intercostal muscles relax pulling the rib cage inwards and downwards. This decreases volume and increases pressure. This forces air out through the bronchioles, trachea and nostrils.