Occupational Safety and Health Administration. 1  Department of Labor, Labor Department, DoL, Labor - the federal department responsible for promoting the working conditions of wage earners in the United States; created in 1913.
The oxygen and carbon dioxide exchange take place in the alveoli. Primary bronchi are located on the upper portion of the lungs, secondary bronchi is located at the center of the lungs and tertiary bronchi is located near bottom of the organs above the bronchioles.
The right main bronchus may be considered as having (1) an upper (eparterial) part, from which the segmental bronchi for the upper lobe arise, and (2) a lower part, from which the segmental bronchi for the middle and lower lobes emerge (fig. 21-4). The left main bronchus divides into two lobar bronchi, one each for the upper and lower lobes. The upper lobar bronchus may be considered as having (1) an upper division and (2) a lower, or lingular, division. The right main bronchus, about 2.5 cm in length, is shorter, wider, and more nearly vertical than the left.