Tonsils & Adenoids (Lymphoid Tissue) of the Pharynx
Bronchioles of the Lungs
From the tertiary bronchi, air is conducted to and from the alveoli (or air sacs) by a series of small, branching tubules called bronchioles
- The bronchioles branch many times on their way to the alveoli, and each division produces tubules that are progressively smaller in diameter (magnified here for display).
- A lobular bronchiole (or preterminal bronchiole), conducts air in and out of a pulmonary lobule (or secondary pulmonary lobule).
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- After entering a pulmonary lobule, a lobular bronchiole divides into three or more terminal bronchioles.
- Terminal bronchioles measure 0.5 – 1 mm (or less) in diameter and have walls made of simple ciliated cuboidal cells, a few smooth muscle cells, and connective tissue. They are too thick for air exchange, so these tubes are considered to be the last of the conducting zone structures.
- Two or three respiratory bronchioles typically branch from each terminal bronchiole. These thin-walled tubules are the first respiratory zone structures, and they, in turn, give rise to alveolar ducts, alveoli, and alveolar sacs.