Newly released sperm cells are nonmotile and are carried from the seminiferous tubules in a fluid secreted by the Sertoli cells. The fluid and sperm flow through the seminiferous tubules, facilitated by peristaltic contractions of the peritubular contractile cells of the lamina propria. They then enter the straight tubules, a short segment of the seminiferous tubule where the epithelium consists only of Sertoli cells. At the mediastinum testis, the fluid and sperm enter the rete testis, an anastomosing system of ducts lined by simple cuboidal epithelium (Plate 87, page 820). From the rete testis, they move into the extratesticular portion of the efferent ductules (ductuli efferentes), the first part of the excurrent duct system, and then into the proximal portion of the duct of the epididymis (ductus epididymis). As the sperm cells move through the 4 to 5 m of the highly coiled duct of the epididymis, they acquire motility and undergo several maturational changes,. These changes include  condensation of nuclear DNA. The head of the sperm decreases in size.  further reduction of cytoplasm. The sperm cells become more slender.  changes in plasma membrane lipids, proteins, and glycosy lation.  alterations in the outer acrosomal membrane (decapacita tion). The surface-associated decapacitation factor is added to inhibit the fertilizing ability of the sperm cells (page 803).
Initiation of sperm cell motility during cell transit through the epididymis is most likely related to changes in the intracellular levels of cyclic adenosine monophosphate (cAMP), calcium ions (Ca2 ), and intracellular pH. These factors regulate flagellar activity through changes in protein phosphorylation, resulting from activities of protein kinases and protein phosphatases. For instance, pharmacologic stimulation of protein kinase A activity increases motility of sperm cells, whereas inhibition of protein phosphatase activity may initiate or stimulate such motility. This suggests that phosphatases have an important role in the regulation of sperm kinetic activity.
Contractions of the smooth muscle that surrounds the progressively distal and larger ducts continue to move the sperm by peristaltic action until they reach the distal portion of the duct of the epididymis, where they are stored before ejaculation.
Sperm can live for several weeks in the male excurrent duct system, but they will survive only 2 to 3 days in the female reproductive tract. They acquire the ability to fertilize the ovum only after some time in the female tract. This process, which involves removal and replacement of glycocalyx components (glycoconjugates) on the sperm membrane, is called capacitation. Capacitation of spermatozoa is described in detail in Chapter 23 (page 840).
Cycle of the Seminiferous Epithelium
Differentiating spermatogenic cells are not arranged at random in the seminiferous epithelium; specific cell types are grouped together. These groupings or associations occur because intercellular bridges are present between the progeny of each pair of type Ap spermatogonia and because the synchronized cells spend specific times in each stage of maturation. All phases of differentiation occur sequentially at any given site in a seminiferous tubule as the progeny of stem cells remain connected by cytoplasmic bridges and undergo synchronous mitotic and meiotic divisions and maturation (see Fig. 22.10).