Accessory sex glands

The paired seminal vesicles secrete a fluid rich in fructose

The seminal vesicles are paired, elongate, and highly folded tubular glands located on the posterior wall of the urinary bladder, parallel to the ampulla of the ductus deferens. A short excretory duct from each seminal vesicle combines with the ampulla of the ductus defer-

x3,000. b. Apical surface of the epithelial cell with its numerous long microvilli (stereocilia). The middle piece of a sperm (S) is evident in the lumen. The small, light circular profiles (arrowheads) are endocytotic vesicles, x 13,000.

ens to form the ejaculatory duct. Seminal vesicles develop as evaginations of the mesonephric (Wolffian) ducts in the region of future ampullae. The wall of the seminal vesicles contains a mucosa, a thin layer of smooth muscle, and a fibrous coat (Fig. 21.26). The mucosa is thrown into numerous primary, secondary, and tertiary folds that increase the secretory surface area. All of the irregular chambers thus formed, however, communicate with the lumen.

The pseudostratified columnar epithelium contains tall, nonciliated columnar cells and short, round cells that rest on the basal lamina. The short cells appear identical to those of the rest of the excurrent duct system. They are the stem cells from which the columnar cells are derived. The columnar cells have the morphology of protein-secreting cells, with a well-developed rER and large secretory vacuoles in the apical cytoplasm.

The secretion of the seminal vesicles is a whitish yellow, viscous material. It contains fructose, which is the principal metabolic substrate for sperm, along with other simple sugars, amino acids, ascorbic acid, and prostaglandins. Al-

testicular artery and vein veins of, ^ pampiniform / plexus chapter 21 i Male Reproductive System 707

though prostaglandins were first isolated from the prostate gland (hence the name), they are actually synthesized in large amounts in the seminal vesicles. Contraction of the smooth muscle coat of the seminal vesicles during ejaculation discharges their secretion into the ejaculatory ducts and helps to flush sperm out of the urethra. The secretory function and morphology of the seminal vesicles are under the control of testosterone.

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