The efferent ductules are lined with pseudostratified columnar epithelium.
In man, approximately 20 efferent ductules connect the channels of the rete testis at the superior end of the mediastinum to the proximal portion of the duct of the epididymis. As the efferent ductules exit the testis, they  become highly coiled and form 6 to 10 conical masses, the coni vasculosi, whose bases form part of the head of the epididymis. The coni vasculosi, each about 10 mm in length, contain the highly convoluted ducts that measure 15 to 20 cm in length. At the base of the cones, the efferent ducts open into a single channel, the duct of the epididymis (see Fig. 22.4).
The efferent ductules are lined with a pseudostratified columnar epithelium that contains clumps of tall and short cells, giving the luminal surface a sawtooth appearance (see Fig. 22.21). Interspersed among the columnar cells are occasional basal cells that serve as epithelial stem cells. The tall columnar cells are ciliated. The short nonciliated cells have numerous microvilli and canalicular invaginations of the apical surface as well as numerous pinocytotic vesicles, membrane-bounded dense bodies, lysosomes, and other cytoplasmic structures associated with endocytotic activity.
Most of the fluid secreted in the seminiferous tubules is reabsorbed in the efferent ductules.
A smooth muscle layer in the excurrent ducts first appears at the beginning of the efferent ductules. The smooth muscle cells form a layer several cells thick in which the cells are arrayed as a circular sheath in the wall of the ductule. Interspersed among the muscle cells are elastic fibers. Transport of the sperm in the efferent ductules is affected largely by both ciliary action and contraction of this fibromuscular layer.
The epididymis is an organ that contains the efferent ductules and the duct of the epididymis.
The epididymis is a crescent-shaped structure that lies along the superior and posterior surfaces of the testis. It measures about 7.5 cm in length and consists of the efferent ductules and the duct of the epididymis and associated vessels, smooth muscles, and connective tissue coverings (Fig. 22.22 and Plate 88, page 822). The duct of the epididymis is a highly coiled tube measuring 4 to 6 m in length. The epididymis is divided into a head, a body, and a tail (see Fig. 22.4). The efferent ductules occupy the head, and the duct of the epididymis occupies the body and tail. Newly produced sperm, which enter the epididymis from the testis, mature during their passage through the duct of the epididymis, acquiring motility and the ability to fertilize an oocyte. During this androgen-dependent maturation process, the head of the sperm is modified by the addition of surface-associated decapacitation factor containing epididymal fluid glycoconjugates. This process, called decapacitation, inhibits the fertilizing ability of the sperm in a reversible inhibitory adenohypophysis testosterone stimulatory GnRH-like peptides spermatogenic cells Leydig cells Sertoli cells ? hypothalamus other CNS centers GnRH FSH LH prolactin inhibin estradiol DHT
FIGURE 22.18 • Diagram depicting the hormonal regulation of male reproductive function. Blue arrows indicate stimulatory action on the system; red arrows indicate inhibitory feedback. See text for explanation.