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The bronchioles 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 of the bronchioles starts as a simple ciliated columnar epithelium and changes to simple ciliated cuboidal epithelium as the bronchioles decreases in size.
Instead of hard cartilage, the bronchi and bronchioles are composed of elastic tissue. The lungs are made up of thirteen different kinds of cells, eleven types of epithelial cell and two types of mesenchymal cell. [13] The epithelial cells form the lining of the tracheal, and bronchial tubes, while the mesenchymal cells line the lungs.
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]
The respiratory bronchioles represent the transition from the conducting portion to the respiratory portion of the respiratory system. The narrow channels are usually less than 2 mm in diameter and they are lined by a simple cuboidal epithelium, consisting of ciliated cells and non-ciliated club cells, which are unique to bronchioles.
Further divisions of the segmental bronchi (1 to 6 mm in diameter) [7] are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. [ 8 ] [ 9 ] Compared to the 23 number (on average) of branchings of the respiratory tree in the adult human, the mouse has only about 13 such branchings.
Their percentage in the trachea is 34%, in the large bronchi 27%, and 10% in the larger of the bronchioles. [1] Basal cells can express a number of different receptors, notably EGFR. [1] Basal cell derived precursors are found as intermediate cells (also known as parabasal, or indetermined cells) between the basal cells and the differentiated ...
In the respiratory tract, from the trachea to the terminal bronchioles, the lining is of respiratory epithelium that is ciliated. [8] The cilia are hair-like, microtubular-based structures on the luminal surface of the epithelium. On each epithelial cell there are around 200 cilia that beat constantly at a rate of between 10 and 20 times per ...
Type I cells are the larger of the two cell types; they are thin, flat epithelial lining cells (membranous pneumocytes), that form the structure of the alveoli. [3] They are squamous (giving more surface area to each cell) and have long cytoplasmic extensions that cover more than 95% of the alveolar surface. [12] [17]