Plate 3 Stratified Epithelia And Epithelioid Tissues

Figure 1, esophagus, monkey, H&E x250

This part of the wall of the esophagus reveals two different epithelia. On the left is the lining epithelium of the esophagus. It is multilayered with squamous surface cells; therefore, it is a stratified squamous epithelium (SS). On the right is the duct of an esophageal gland cut in several planes. By examining a region where the plane of section is at a right angle to the surface, the true character of the epithelium becomes apparent. In this case, the epithelium consists of two cell layers with cuboidal surface cells; thus, it is stratified cuboidal epithelium (SC).

This shows a portion of the duct of a sweat gland just before the duct enters the stratified squamous epithelium (SS) of the skin. The dashed line traces the duct within the epidermis. This duct also consists of a stratified cuboidal ep ithelium (SC) in two layers; the cells of the inner layer (the surface cells) appear more or less square. Because the epidermal surface cells are not included in the field, the designation stratified squamous cannot be derived from the information offered by the micrograph.

Figure 3, anorectal junction, human, H&E X300.

The area shown here is the terminal part of the intestine. The luminal epithelium on the left is typical simple columnar (SCol) epithelium of the colon. This epithelium undergoes an abrupt transition (arrowhead) to a stratified cuboidal epithelium (StCu) at the anal canal. Note the general cuboidal shape of most of the surface cells (arrows)

and the underlying layers of cells. The simple columnar epithelium on the left is part of an intestinal gland that is continuous with the simple columnar epithelium at the intestinal luminal surface. The connective tissue (CT) at this site is heavily infiltrated with lymphocytes, giving it an appearance unlike the connective tissue of other specimens on this page.

Figure 4, urinary bladder, monkey, H&E x400.

The epithelium of the urinary bladder is called transitional epithelium, a stratified epithelium that changes in appearance according to the degree of distension of the bladder. In the nondistended state, as here, it is about four or five cells deep. The surface cells are large and dome shaped (asterisks). The cells immediately under the surface cells are pear shaped and slightly smaller. The deepest cells are the smallest, and their nuclei appear more crowded. When the bladder is distended, the superficial cells are stretched into squamous cells, and the epithelium is reduced in thickness to about three cells deep. The bladder wall usually contracts when it is removed, unless special steps are taken to preserve it in a distended state. Thus, its appearance is usually like that in Figure 4.

Figure 4, urinary bladder, monkey, H&E x400.

The epithelium of the urinary bladder is called transitional epithelium, a stratified epithelium that changes in appearance according to the degree of distension of the bladder. In the nondistended state, as here, it is about four or five cells deep. The surface cells are large and dome shaped (asterisks). The cells immediately under the surface cells are pear shaped and slightly smaller. The deepest cells

Figure 6, endocrine pancreas, human, H&E X450.

Cells of the endocrine islet (of Langerhans) (En) of the pancreas also have an epithelioid ammgement. The cells are in contact but lack a free surface, although they have developed from an epithelial surface by invagination. In contrast, the surrounding alveoli of the exocrine pancreas (Ex), which developed from the same epithelial surface, are made up of cells with a free surface onto which the secretory product is discharged. Capillaries (C) are prominent in endocrine tissues. Similar examples of epithelioid tissue are seen in the adrenal and the parathyroid and pituitary glands, all of which are endocrine glands.

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