Key

BV, blood vessels CT, connective tissue L, lumen of ductus deferens LP, lamina propria

Lu, lumen of blood vessel N, nerve

SM(C), circular layer of smooth muscle SM(L), longitudinal layer of smooth muscle arrowheads, stereocilia arrows (Fig. 2), basal cell nucleus asterisks (Fig. 1), small arteries supplying ductus deferens

The prostate gland is the largest accessory sex gland. It consists of 30 to 50 tubuloalveolar glands that surround the proximal urethra. Because of this relationship, a common condition in later life, benign prostatic hyperplasia, can result in partial or total obstruction of the urethra.

The prostatic glands are arranged in three concentric layers: a mucosal layer, a submucosal layer, and a peripheral layer containing the main prostatic glands. The mucosal glands secrete directly into the urethra; the other two sets of glands deliver their secretions through ducts that open into the prostatic sinuses on the posterior wall of the urethra. All of the glands are made up of a pseudostratified columnar epithelium that secretes several components of the semen, including acid phosphatase, citric acid (a nutrient for sperm), and fibrinolysin (which keeps the semen liquified). Aggregations of dead epithelial cells and precipitated secretory products form concretions in the alveoli of the glands; these are a characteristic feature that aids in recognition of the prostate.

The stroma is characterized by numerous small bundles of smooth muscle, so that it can also be described as a fibromus-cular stroma. Contraction of this muscle occurs at ejaculation, forcing the secretion into the urethra. Surrounding the gland is a fibroelastic capsule that also contains small bundles of smooth muscle.

Figure 1, prostate, human H&E x47.

A portion of the prostate gland in shown in this low-magnification micrograph. A small section of the capsule (Cap) of the gland is seen in the upper left corner. The rest of the field is filled with the glandular and stromal components of the prostate. The secretory tubuloalveoli of the prostate gland vary greatly in form, as is evident in the figure. They may appear as tubes, as isolated alveoli, as alveoli with branches, or as tubes with branches. Tangential sections through alveoli may even produce the appearance of "epithelial islands" (arrowheads) in the lumen of the alveoli. This is due to the extremely uneven contour of the

Figure 2, prostate, human, H&E x178; upper inset x350; lower inset x650.

In this higher magnification view of a portion of the prostate gland, the fibromuscular stroma is clearly seen both immediately subtending the secretory epithelium of the tubuloalveoli as well as in deeper, nonsecretory areas. In the upper inset, corresponding to the larger rectangle, the intensity of the staining of the smooth muscle (SM) clearly distinguishes it from the fibrous stromal connective tissue with which it is intimately intermingled. There are no clearly outlined bundles or layers of smooth muscle in the prostate; rather, it is randomly arrayed throughout the epithelial surface. It should also be noted that many of the alveoli may appear rudimentary in structure (arrows). These are simply in an inactive state and are increasingly observed in older individuals. As noted above, aggregations of dead epithelial cells and precipitated secretions form prostatic concretions (C) in the lumina of the alveoli; these gradually increase in number and size with age. The concretions stain with eosin and may have a concentric lamellar appearance, as is clearly shown in the concretion in the lower right. With time, they may become impregnated with calcium salts and thus be easily recognized in x-rays of the lower abdomen.

stroma. Concretions (C) are again evident in the lumina of alveoli, in one instance compressing the epithelium to a degree that makes it nearly unrecognizable. The lower inset, corresponding to the smaller rectangle, clearly demonstrates the pseudostratified columnar nature of the prostatic epithelium (Ep). Well-delineated basal cells (arrowheads) are seen along with the taller columnar secretory cells. A small blood vessel immediately subtending the epithelium is recognizable by the red blood cells in its lumen. A lymphocytic infiltration appears to fill the stroma along the lower border of Figure 2, suggesting an inflammatory process occurring in the prostate gland.

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