Editing Club cell (section)

==Function==
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&nbsp;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. In addition to being structurally diverse, club cells are also functionally variable. One major function they carry out is the synthesis and secretion of the material lining the bronchiolar [[lumen (anatomy)|lumen]]. This material includes glycosaminoglycans, proteins such as [[lysozyme]]s, and conjugation of the secretory portion of IgA antibodies. These play an important defensive role, and they also contribute to the degradation of the mucus produced by the upper airways. The heterogeneous nature of the dense granules within the club cell's cytoplasm suggests that they may not all have a secretory function. Some of them may contain lysosomal enzymes, which carry out a digestive role, either in defense: Club cells engulf airborne toxins and break them down via their cytochrome P-450 enzymes (particularly [[CYP4B1]], which is only present in the club cells) present in their smooth endoplasmic reticulum; or in the recycling of secretory products. Club cells are mitotically active. They divide and differentiate to form both ciliated and non-ciliated epithelial cells.