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The terminal bronchioles are the most distal segment of the conducting zone. They branch off the lesser bronchioles. Each of the terminal bronchioles divides to form respiratory bronchioles which contain a small number of alveoli. Terminal bronchioles are lined with simple ciliated cuboidal epithelium containing club cells. Club cells are non ...
In humans and other mammals, the anatomy of a typical respiratory system is the respiratory tract.The tract is divided into an upper and a lower respiratory tract.The upper tract includes the nose, nasal cavities, sinuses, pharynx and the part of the larynx above the vocal folds.
The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES) [6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here. [7]
Bronchial anatomy showing terminal bronchioles (BT) leading to respiratory bronchioles (BR) and alveolar ducts (DA) that open into alveolar sacs containing out pockets of alveoli (A) separated by alveolar septa (AS) The alveoli are first located in the respiratory bronchioles as scattered outpockets, extending from their lumens.
Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated. Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent starting at the bronchioles. The same goes for goblet cells, although there are scattered ones in the first bronchioles.
The conducting zone of the respiratory tract ends at the terminal bronchioles when they branch into the respiratory bronchioles. This marks the beginning of the terminal respiratory unit called the acinus which includes the respiratory bronchioles, the alveolar ducts, alveolar sacs, and alveoli. [27] An acinus measures up to 10 mm in diameter. [28]
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Plant structures or organs fulfil specific functions, and those functions determine the structures that perform them. Among terrestrial (land) plants, the vascular and non-vascular plants (Bryophytes) evolved independently in terms of their adaptation to terrestrial life and are treated separately here (see Bryophytes ).