A bronchus, also known as a main or primary bronchus, is a passage of airway in the respiratory tract that conducts air into the lungs. There is a right bronchus and a left bronchus and these bronchi branch into smaller secondary and tertiary bronchi which branch into smaller tubes, known as bronchioles.No gas exchange takes place in the bronchi.he secondary bronchi divide further into tertiary bronchi, (also known as segmental bronchi), each of which supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung separated from the rest of the lung by a septum of connective tissue.