Pseudostratified
columnar epithelium, transitional epithelium, and glandular epithelium cannot
be classified as easily as typical epithelium. Pseudostratified columnar
epithelium, found in the trachea, bronchi and large bronchioles, and parts of
the male reproductive tract, is characterized by the fact that all of its cells
are in contact with the basement membrane, but not all of the cells reach the
surface. It is called pseudostratified because it gives the false (“pseudo”)
impression that it is a multilayered stratification, since the nuclei of the
cells appear to be at several different levels. Transitional epithelium lines
the urinary tract, including the ureters, urinary bladder, urethra, and calyxes
of the kidneys. The cells vary in shape depending on the amount of fluid the
organ contains. For example, when the urinary bladder contains a large quantity
of urine, the cells are stretched out and assume a flat, squamous appearance.
When the bladder is empty, the cells have a cuboidal or slightly columnar
shape. Glandular epithelium cells are specialized for the synthesis, storage,
and secretion of chemical substances, such as saliva or digestive juices. These
glands are called exocrine glands.
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