the secondary bronchi that branch off the primary bronchi are also called bronchial veins.
the secondary bronchi that branch off the primary bronchi are also called?
bronchial veins
the primary bronchi, in each lung, which are the left and right bronchus, give rise to secondary bronchi known as lobar bronchi. these in turn give rise to tertiary bronchi ("tertiary" meaning "third"), known as segmental bronchi. the segmentary bronchi subdivide into fourth order, fifth order and sixth order segmental bronchi before dividing into the bronchioles. these are histologically distinct from the bronchi in that their walls do not have hyaline cartilage and they have club cells in their epithelial lining. the epithelium starts as a simple ciliated columnar epithelium and changes to simple ciliated cuboidal epithelium as the bronchioles decreases in size. the diameter of the bronchioles is often said to be less than 1 mm, though this value can range from 5 mm to 0.3 mm. as stated, these bronchioles do not have hyaline cartilage to maintain their patency. instead, they rely on elastic fibers attached to the surrounding lung tissue for support. the inner lining (lamina propria) of these bronchioles is thin with no glands present, and is surrounded by a layer of smooth muscle. as the bronchioles get smaller they divide into terminal bronchioles. these bronchioles mark the end of the conducting zone, which covers the first division through the sixteenth division of the respiratory tract. alveoli only become present when the conducting zone changes to the respiratory zone, from the sixteenth through the twenty-third division of the tract.
bronchiole
during inhalation air enters the trachea via the nostrils and mouth, and continues to just beyond the syrinx at which point the trachea branches into two primary bronchi, going to the two lungs (fig. 16). the primary bronchi enter the lungs to become the intrapulmonary bronchi, which give off a set of parallel branches called ventrobronchi and, a little further on, an equivalent set of dorsobronchi (fig. 16). the ends of the intrapulmonary bronchi discharge air into the posterior air sacs at the caudal end of the bird. each pair of dorso-ventrobronchi is connected by a large number of parallel microscopic air capillaries (or parabronchi) where gas exchange occurs (fig. 16). as the bird inhales, tracheal air flows through the intrapulmonary bronchi into the posterior air sacs, as well as into the "dorso"bronchi, but not into the "ventro"bronchi (fig. 18). this is due to the bronchial architecture which directs the inhaled air away from the openings of the ventrobronchi, into the continuation of the intrapulmonary bronchus towards the dorsobronchi and posterior air sacs. from the dorsobronchi the inhaled air flows through the parabronchi (and therefore the gas exchanger) to the ventrobronchi from where the air can only escape into the expanding anterior air sacs. so, during inhalation, both the posterior and anterior air sacs expand, the posterior air sacs filling with fresh inhaled air, while the anterior air sacs fill with "spent" (oxygen-poor) air that has just passed through the lungs.
respiratory system