The basal surface of the ductule, in contrast, has a smooth contour (see figure below and inset). Some of the cells, generally the tall columnar cells, possess cilia (C) (inset). Whereas the ciliated cells aid in moving the contents of the tubule toward the epididymis, the cells with the microvilli are largely responsible for absorbing fluid from the lumen. In addition to the columnar and cuboidal cells, basal cells are also present; thus, the epithelium is designated pseudostratified columnar. The basal cells possess little cytoplasm and presumably serve as stem cells.
The efferent ductules possess a thin layer of circularly arranged smooth muscle cells (SM, inset). The muscle is close to the basal surface of the epithelial cells, being separated from it by only a small amount of connective tissue (CT, inset). Because of this close association, the smooth muscle may be overlooked or misidentified as connective tissue. Smooth muscle facilitates movement of luminal contents of the ductule to the ductus epididymis.
They are readily distinguished from the spherical nuclei of the basal cells that lie close to the basement membrane. Other conspicuous features of the columnar cells include a very large supranuclear Golgi apparatus (not seen at the magnification offered here), pigment accumulations (P), and numerous lysosomes, demonstrable with appropriate techniques.
Because of the unusual height of the columnar cells and, again, the tortuosity of the duct, an uneven lumen appears in some sites; indeed, even “islands” of epithelium can be encountered in the lumen (see arrows, figure above). Such profiles are accounted for by sharp turns in the duct where the epithelial wall on one side of the duct is partially cut. For example, a cut in the plane of the double-headed arrow indicated in this figure would create such an isolated epithelial island.
A thin layer of smooth muscle circumscribes the duct and appears similar to that associated with the efferent ductules. In the terminal portion of the epididymis, however, the smooth muscle acquires a greater thickness, and longitudinal fibers are also present. Beyond the smooth muscle coat there is a small amount of connective tissue (CT) that binds the loops of the duct together and carries the blood vessels (BV) and nerves.
The ductus (vas) deferens continues from the duct of the epididymis as a thick-walled muscular tube that leaves the scrotum and passes through the inguinal canal as a component of the spermatic cord. At the deep inguinal ring, it continues into the pelvis and, behind the urinary bladder, joins with the excretory duct from the seminal vesicle to form the ejaculatory duct. The ejaculatory duct then pierces the prostate gland and opens into the urethra. Mature sperm are stored in the terminal portion (tail) of the ductus epididymis. These sperm are forced into the ductus deferens by intense contractions of the three smooth muscle layers of the ductus deferens following appropriate neural stimulation. Contraction of the smooth muscle of the ductus deferens continues the movement of the sperm through the ejaculatory duct into the urethra during the ejaculatory reflex. The seminal vesicles (see Plate 91) are not storage sites for sperm but, rather, secrete a fructose-rich fluid that becomes part of the ejaculated semen. Fructose is the principal metabolic substrate for sperm.
Spermatic cord, human, H&E 80.
A cross section through the ductus deferens and some of the vessels and nerves that accompany the duct in the spermatic cord are shown in this figure. The wall of the ductus deferens is extremely thick, mostly because of the presence of a large amount of smooth muscle. The muscle contracts when the tissue is removed, causing the mucosa to form longitudinal folds. For this reason, in histologic sections, the lumen (L) usually appears irregular in cross section.