FIGURE 22.16 • Schematic drawing of the Sertoli cell and its relationship to adjacent spermatogenic cells. This drawing shows the Sertoli–to–Sertoli junctional specialization between adjacent Sertoli cells and the Sertoli–to–spermatid junctional specialization between the Sertoli cell and late spermatids. The Sertoli–to–Sertoli junctional complex is an adhesion device that includes a tight junction that contributes to the blood–testis barrier. The junctional specialization between the Sertoli cell and late spermatids residing in deep recesses within the apical cytoplasm is an adhesion device only. Lateral processes of the Sertoli cells extend over the surface of the spermatocytes and spermatids. Note the ultrastructural features of the Sertoli cell, including the microtubule arrays and characteristic shape of the nucleus and its karyosome. (Reprinted with permission from Bloom W, Fawcett DW. A Textbook of Histology.
Philadelphia: WB Saunders, 1975.)
A similar-appearing junctional complex in the Sertoli cell is also present at the site where the spermatids are attached. However, no tight junction is present, and the spermatid lacks flattened cisternae of sER and actin filament bundles (see Figs. 22.16 and 22.17). Other junctional specializations of the Sertoli cells include gap junctions between Sertoli cells, desmosome-like junctions between Sertoli cells and early-stage spermatogenic cells, and hemidesmosomes at the Sertoli cell–basal lamina interface.
The Sertoli cell–to–Sertoli cell junctional complex divides the seminiferous epithelium into basal and luminal compartments.
The Sertoli cell–to–Sertoli cell junctions establish two epithelial compartments, a basal epithelial compartment and a luminal compartment. Spermatogonia and early primary spermatocytes are restricted to the basal compartment (i.e., between the Sertoli cell–to–Sertoli cell junctions and the basal lamina). More mature spermatocytes and spermatids are restricted to the luminal side of the Sertoli cell–to–Sertoli cell junctions. Early spermatocytes produced by mitotic division of type B spermatogonia must pass through the junctional complex to move from the basal compartment to the luminal compartment. This movement occurs via the formation of a new junctional complex between Sertoli cell processes that extend beneath the newly formed spermatocytes, followed by the breakdown of the junction above them. Thus, in the differentiation of the spermatogenic cells, the processes of meiosis and spermiogenesis occur in the luminal compartment.
In both compartments, spermatogenic cells are surrounded by complex processes of the Sertoli cells. Because of the unusually close relationships between Sertoli cells and differentiating spermatogenic cells, it has been suggested that Sertoli cells serve as “nurse,” or supporting, cells (i.e., they function in the exchange of metabolic substrates and wastes between the developing spermatogenic cells and the circulatory system).
In addition, Sertoli cells phagocytose and break down the residual bodies formed in the last stage of spermiogenesis. They also phagocytose any spermatogenic cells that fail to differentiate completely.
The Sertoli cell–to–Sertoli cell junctional complex is the site of the blood–testis barrier.
In addition to the physical compartmentalization described above, the Sertoli cell–to–Sertoli cell junctional complex also
FIGURE 22.17 • Electron micrograph of Sertoli cell junctions.