The seminiferous cords are of considerably smaller diameter than the tubules of the adult and are composed of two cell types: the gonocyte, or first-generation spermatogonium, derived from the primordial germ cell that migrates from the yolk sac to the developing gonad in the embryo; and a cell that resembles the Sertoli cell of the adult. The latter cell type predominates and constitutes the bulk of the cord. The cells are columnar, and their nuclei are close to the basement membrane. The gonocytes (G) are the precursors of the definitive germ cells, or spermatogonia. They are round cells
Mediastinum testis, testis, monkey, H&E 65.
In the posterior portion of the testis, the connective tissue of the tunica albuginea extends more deeply into the organ. This inward extension of connective tissue is called the mediastinum testis. It contains a network of anastomosing channels called the rete testis. Only a small portion of the mediastinum testis (MT) is evident in the figure. The area includes, however, a few seminiferous tubules (ST) in the upper portion of the micrograph
Straight tubule, testis, monkey, H&E 400.
The straight tubule or tubulus rectus (TR) in this figure appears to end on one side before it ends on the other. This simply reflects the angle of section. When the straight tubule ends, however, the epithelial lining suddenly becomes cuboidal. This represents the rete testis, which constitutes an anastomosing system of channels that lead to the efferent ductules. The that have a centrally placed, spherical nucleus. The cytoplasm takes little stain and usually appears as a light ring around the nucleus. This gives the gonocyte a distinctive appearance in histologic sections (inset). Generally, the gonocytes are found at the periphery of the cord, but many are also found more centrally. The gonocytes give rise to spermatogonia that begin to proliferate in males between the ages of 10 and 13 years. The seminiferous epithelium then becomes populated with cells at various stages of spermatogenesis, as seen in the adult.
The seminiferous cords are surrounded by one or two layers of cells with long processes and flat nuclei. They resemble fibroblasts at the ultrastructural level and give rise to the myoid peritubular cells of the adult.
The interstitial cells (of Leydig) are conspicuous in the newborn, a reflection of the residual effects of maternal hormones. Leydig cells, however, regress and do not become conspicuous again until puberty. In this preparation, the Leydig cells (LC) can be seen between the cords (inset). They are ovoid or polygonal and are closely grouped, so that adjacent cells are in contact with each other. Overall, they have the same appearance as the Leydig cells of the adult.
and, fortuitously, the site where one of the seminiferous tubules terminates and joins the rete testis (RT). This can be recognized in the area delineated by the rectangle, which is shown at higher magnification in figure below. As noted above, the seminiferous tubules are arranged in the form of a loop, with each end joining the rete testis. The seminiferous tubules open into the rete testis by way of a straight tubule. Straight tubules are very short and are lined by Sertoli-like cells; no germ cell component is present.
epithelial lining cells of the rete are sometimes more squamous than cuboidal or, occasionally, may be low columnar in appearance. Typically, they possess a single cilium; however, this is difficult to see in routine H&E preparations.
The connective tissue of the mediastinum is very dense but exhibits no other special features, nor is smooth muscle present. Adipose cells (AC) and blood vessels (BV), particularly veins of varying size, are present within the connective tissue.