Bird, lung (Gross, Medium)

Structure List Secondary bronchi Parabronchi High Magnification View

The two PRIMARY BRONCHI bifurcate at the trachea and enter the lung. A primary bronchus continues through the lung as a MESOBRONCHUS. SECONDARY BRONCHI arise from the mesobronchus and in turn give rise to TERTIARY BRONCHI (or parabronchi). The parabronchi are continuous with other secondary bronchi. Thus, a complete air-conducting loop is formed. Air vesicles, called ATRIA, project radially from the tertiary bronchi. Gas exchange does not occur in the air sacs, but instead occurs in the air capillaries which branch off the parabronchi in the lung. The air capillaries are surrounded by dense capillary beds.