Transition of bronchiole to respiratory bronchiole

This image shows the transitions that occur as a bronchiole becomes a terminal bronchiole which, in turn, becomes a respiratory bronchiole. Because alveoli bud directly from the lumen of a respiratory bronchiole, this passageway is a portion of the respiratory portion of the respiratory system. 40x

This image shows the transitions that occur as a bronchiole becomes a terminal bronchiole which, in turn, becomes a respiratory bronchiole. Because alveoli bud directly from the lumen of a respiratory bronchiole, this passageway is a portion of the respiratory portion of the respiratory system. 40x

This image shows the transitions that occur as a bronchiole becomes a terminal bronchiole which, in turn, becomes a respiratory bronchiole. Because alveoli bud directly from the lumen of a respiratory bronchiole, this passageway is a portion of the respiratory portion of the respiratory system. 40x

Many alveoli are visible. Alveoli (black Xs + arrows) whose lumens are directly continuous with the lumen of a bronchiole establish this bronchiole as a “respiratory” variety rather than “terminal,” since gaseous exchange occurs through alveolar walls. Other alveoli (blue Xs) belong to other respiratory bronchioles or alveolar ducts.