![]() As further branching occurs, epithelial height lowers to produce more cuboidal ciliated cells. The larger bronchioles are lined with ciliated pseudostratified columnar cells typical of the classical respiratory epithelium. Despite this, smooth muscle is still present in the lamina propria of bronchioles and contributes to small airway closure in obstructive lung disease like asthma. Histologyīronchioles are defined by their lack of hyaline cartilage, instead relying on the tension from surrounding lung tissue for dilatory support. Each respiratory bronchiole then supplies 2-11 alveolar ducts which in turn each supply 4-5 alveolar sacs. Thus, the respiratory bronchiole represents the first part of the respiratory division. These respiratory bronchioles are noted for thin-walled outpouchings from the lumen known as alveoli where primary gas exchange occurs. These transfer air but lack glands or alveoli with the most distal segment of these termed terminal bronchioles.Įach of these terminal bronchioles themselves gives rise to several generations of respiratory bronchioles. Following the tertiary segmental bronchi, there are 20-25 branching generations of conducting bronchioles which are typically <1 mm in diameter. The bronchioles typically begin beyond the tertiary segmental bronchi and are described as conducting bronchioles. ![]()
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