Page 138 - Atlas of Histology with Functional Correlations

barrier against the hypertonic and cytotoxic effect of urine in the bladder

and underlying connective tissue.

FIGURE 4.10 | Stratified Squamous

Nonkeratinized Epithelium: Esophagus

Stratified squamous epithelium is characterized by numerous cell layers, with the
outermost layer consisting of flat or squamous cells, which contain nuclei and
are alive. The thickness of the epithelium varies among different regions of the
body, and, as a result, the composition of the epithelium also varies. Illustrated in

this figure is an example of the moist, nonkeratinized stratified squamous
epithelium (1) that lines the esophagus as well as the oral cavity, vagina, and
anal canal.

Cuboidal or low columnar basal cells (5) are located at the base of the

stratified epithelium. The cytoplasm is finely granular, and the oval, chromatin-
rich nucleus occupies most of the cell. Cells in the intermediate layers of the
epithelium are polyhedral (4) with round or oval nuclei and more visible cell
cytoplasm and membranes. Mitoses (6) are frequently observed in the deeper

cell layers and in the basal cells (5). Cells and their nuclei become progressively
flatter as the cells migrate toward the free surface of the epithelium. Above the
polyhedral cells (4) are several rows of flattened or squamous cells (3).

A fine basement membrane (7) separates the epithelium (1) from the

underlying connective tissue, the lamina propria (2). Papillae (10) or
extensions of connective tissue indent the lower surface of the epithelium (1),
giving it a characteristic wavy appearance. The connective tissue (2) contains
collagen fibers (11), fibrocytes (9), capillaries (12), and arterioles (8).

In areas where stratified squamous epithelium is exposed to increased wear

and tear, the outermost layer, called the stratum corneum, becomes thick and
keratinized, as illustrated in the epidermis of the palm in Figure 4.11.

An example of thin, stratified squamous epithelium without connective
tissue papillae indentation is found in the cornea of the eye; the surface

underlying the epithelium is smooth. This type of epithelium is only a few cell
layers thick, but it has the characteristic arrangement of basal columnar,
polyhedral, and superficial squamous cells.

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