Page 134 - Atlas of Histology with Functional Correlations

FIGURE 4.7 | Pseudostratified Columnar Ciliated

Epithelium: Respiratory Passages—Trachea

Pseudostratified columnar ciliated epithelium lines the upper respiratory

passages, such as the trachea and bronchi. In this type of epithelium, the cells
appear to form several layers. Serial sections show that all cells reach the
basement membrane (4, 13); however, because the epithelial cells are of
different shapes and heights, not all reach the surface. For this reason, this type

of epithelium is called pseudostratified rather than stratified.

Numerous motile and closely spaced cilia (1, 8) (cilium, singular) cover all
cell apices of the ciliated cells, except those of the light-staining, oval goblet
cells (3, 11) that are interspersed among the ciliated cells. Each cilium arises

from a basal body (9), whose internal morphology is identical to the centriole.
The basal bodies (9) are located directly beneath the apical cell membrane and
are adjacent to each other; they often give the appearance of a continuous dark,
apical membrane (9).

In pseudostratified epithelium, the deeper nuclei belong to the intermediate

and short basal cells (12). The more superficial, oval nuclei belong to the
columnar ciliated cells (1, 8). The small, round, heavily stained nuclei, without
any visible surrounding cytoplasm, are those of lymphocytes (2, 10). These cells
migrate from the underlying connective tissue (5) through the epithelium.

A clearly visible basement membrane (4, 13) separates the pseudostratified
epithelium from the underlying connective tissue (5). Visible in the connective
tissue (5) are fibrocytes (5a), dense collagen fibers (5b), scattered lymphocytes,
and small blood vessels (14). Deeper in the connective tissue are glands with
mucous acini (6) and serous acini (7, 15). These provide secretions that moisten

the respiratory passages.

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