Usually, this 5-inch body part is open to allow passage of air to & from the lungs
... of oxygen and carbon dioxide, about 5 to 8 liters (about 1.3 to 2.1 
gallons) of air per... [DOC] [TLE] Defense Mechanisms of the Respiratory System - Lung and Airway ... [PAR] Commonly searched drugs ... Inevitably, this air (which would weigh more than 
20 kilograms [44 pounds]) ... to 5 microns (0.000118 to 0.000196 inches) in 
diameter, penetrate to the deep lung.