Inhalation is the process of taking air into the lungs. For this to occur, the air pressure inside the lungs must be lower than that of the external atmosphere as air flows from areas of higher pressure to lower pressure. Exhalation is the process of expelling air out of the lungs. For this to occur, the air pressure inside the lungs must be higher than that of the external atmosphere as air flows from areas of higher pressure to ones of lower pressure.
