The respiratory tree is so named because it has the appearance of an inverted tree, with its trunk and branches. It is essentially a tubular structure connecting the larynx to the alveoli of the lungs.
This tubular structure is lined with a ciliated epithelium. The tubes are kept open by a series of ring-like structures of cartilage.
The "trunk" of the tree is the trachea. The trachea extends from the inferior margin of the larynx, down through the neck, and into the center of the thorax.
In the center of the thorax, the trachea divides into right and left primary bronchi. The right is somewhat more vertical than the left.
Therefore, when a person accidentally aspirates ("breathes in") a foreign object, it is more likely to be found in the right primary bronchus than the left.
Each primary bronchus extends laterally into the substance of the appropriate lung. Within each lung, the tubular structure divides, subdivides, and divides again, up to about 30 times.
Thus, the tubes become more and more numerous and smaller and smaller in size. At the terminals of the branching tubes are groups of spherical alveoli.
This gives the appearance of a bunch of grapes. A variety of situations may occlude (close or shut off) these tubular air passageways. A foreign object may be aspirated ("breathed in").
The wall of the tube may constrict in a bronchial spasm. The lining of the tube may become swollen with fluid and close the passageway.
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