Page 136 - Atlas of Histology with Functional Correlations

Transitional epithelium (1) is found exclusively in the excretory passages of

the urinary system. It covers the lumina of renal calyces, pelvis, ureters, and
bladder. This stratified epithelium is composed of several layers of similar cells.
In an empty bladder, the epithelial cells appear cuboidal and extend into the
lumen. These cells are frequently called umbrella or dome cells. The epithelium
continuously changes its shape in response to either stretching, as a result of

fluid accumulation, or contraction during voiding of urine.

In a relaxed, unstretched condition, the surface cells (7) are usually cuboidal
and bulge out into the lumen. Frequently, binucleate (two nuclei) cells (6) are
visible in the superficial layers or surface cells (7) of the bladder.

Transitional epithelium (1) rests on a connective tissue (3, 8) layer,
composed primarily of fibroblasts (8a) and collagen fibers (8b). Between the
connective tissue (3, 8) and the transitional epithelium (1) is a thin basement
membrane (2). The base of the epithelium is not indented by connective tissue
papillae, and it exhibits an even contour.

Small blood vessels, venules (4, 11), and arterioles (9) of various sizes are
present in the connective tissue (3, 8). Deeper in the connective tissue are strands
of smooth muscle fibers (5, 10), sectioned in both cross (5) and longitudinal
(10) planes. The muscle layers in the bladder are located deep to the connective

tissue (3, 8).

FIGURE 4.8 ■ Transitional epithelium: bladder (unstretched or relaxed). Stain:
hematoxylin and eosin. High magnification.

FIGURE 4.9 | Transitional Epithelium: Bladder

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