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.
It divides into two principle bronchi, tubes which conduct air into the lungs, and they divide into two lobar bronchi for the left lung, and into four lobar bronchi for the right lung. These further divide into smaller bronchi and bronchioles within the lung tissue. The structure of the larger bronchi is identical to that of the trachea. On the smaller bronchi the C-shaped cartilage rings are gradually replaced by irregular plaques of cartilage. Bronchioles have no cartilage at all. The bronchioles are less than 1mm in diameter, and undergo further divisions, the last of which is characterised by the loss of goblet cells.