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The airway warms and moistens the air prior to gas exchange as it travels from the nasal passage towards the distal lung, while protecting the distal lung from harmful pathogens and environmental insults. See MoreThe human airway is covered with a continuous epithelial sheet that differs in morphology and cellular composition between the conducting and respiratory zones.

The conducting zone includes regions that do not participate in gas exchange: the nasal passage, trachea, main bronchi, intra-pulmonary bronchi and bronchioles. The proximal regions exhibit a columnar, pseudostratified morphology, while the height of this epithelium decreases in more distal regions of the bronchi and bronchioles, where it resembles a cuboidal epithelium. The major cell types of the conducting zone are goblet cells that produce and secrete mucus, ciliated cells that promote mucus motility through coordinated movement of their apical cilia, and basal cells that line the basement membrane and do not contact the apical surface of the epithelium.

The respiratory zone consists of the respiratory bronchioles, alveolar ducts and alveolar sacs, and is the site of gas exchange between the air within the lung and the blood within pulmonary capillaries. The alveolar epithelium is lined with type I and II alveolar epithelial cells (AECs). The alveolar cells fuse to endothelial cells by their basal membranes to form the gas exchange barrier.

Read this mini-review to learn more about Airway Epithelial Cells.

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