The bronchi have a cylindrical shape and they are located between the bifurcation of the trachea and bronchioles. The bronchi enable and ensure the passage of air from the trachea to the bronchioles and the alveoli. There are two main bronchi within the human body: right bronchus and left bronchus.

The bronchi are a part of the zone responsible for conducting air. The conducting zone includes the windpipe and pharynx and it is solely responsible for moving air in and out of the body.

Moreover, the bronchi are airways that contain cartilaginous walls. The cartilage is a connective tissue that supports the physical processes such as preventing collapsing of the bronchi during inhalation and exhalation. The amount of cartilage in the walls of the bronchi gradually decreases and disappears after the point where the bronchi divide into smaller airways called bronchioles.

The bronchioles are the small terminal branches of the airways in the lungs. They have a diameter of less than one millimetre. The bronchioles branch further up to present, at their ends, the pulmonary alveoli, which, in turn, branch off into sacks, or infundibula (noncellular small structures in the form of a bag arranged in a cluster, which represent the terminal part of the respiratory tract), through whose walls gaseous exchanges take place with the blood. The walls of the bronchioles are formed of smooth muscle and elastic connective tissue and they are characterized by a cubic epithelium cell.

What are the bronchi and bronchioles?

The structure of the main bronchi resembles the shape of a tree, from which the common definition of the bronchial tree is derived. Following the branching of the bronchial tree, there is an extra pulmonary stretch on each side: it consists of a main bronchus, one exterior and interior bronco, two or three lobar bronchi and some segmental bronchi from which originate the bronchi terminals. The bronchial branches become gradually smaller towards the bronchioles, which end in the alveoli.

The right main stem bronchus is shorter and wider and measures about 2.5 centimetres. The right bronchus appears as a direct continuation of the trachea. On the other hand, the left bronchus is longer and measures about 5 centimetres in length. The right and left bronchi then divide into lobar bronchi and then continue into segmental or tertiary bronchi. Veins, arteries and lymphatics also enter the lungs together with the bronchi. The portion of the lung that is supplied by a segmental bronchus and its adjacent blood vessels is referred to as a bronchopulmonary segment.

The bronchi are externally covered by a protective sheath and fibro cartilaginous muscle, which gives them a semi-rigid appearance. Internally, the bronchi are covered by certain glands and a mucous membrane, whose task is to eliminate bacteria, dust, and all particles inhaled from the external environment.

What functions do the bronchi and bronchioles serve?

The task of the bronchi is to ensure the passage of air from the trachea to the bronchioles. The bronchioles allow gas exchange with blood: their many branches branch out into the alveoli and alveolar infundibula. In a sense, the bronchioles represent the terminal part of the respiratory tract.