Each lobule of the testis consists of one to four seminiferous tubules, in which sperm are produced, and a connective tissue stroma, in which Leydig (interstitial) cells are contained (Fig. 22.5). Each tubule within the lobule forms a loop and, because of its considerable length, is highly convoluted, actually folding on itself within the lobule. The ends of the loop are located near the mediastinum of the testis, where they assume a short straight course. This part of the seminiferous tubule is called the straight tubule (tubulus rectus). It becomes continuous with the rete testis, an anastomosing channel system within the mediastinum.
The seminiferous tubules consist of a seminiferous epithelium surrounded by a tunica propria.
Each seminiferous tubule is approximately 50 cm long (range, 30 to 80 cm) and 150 to 250 m in diameter. The seminiferous epithelium is an unusual and complex stratified epithelium composed of two basic cell populations:  Sertoli cells, also known as supporting, or sustentacular, cells. These cells do not replicate after puberty. Sertoli cells are columnar cells with extensive apical and lateral processes that surround the adjacent spermatogenic cells and occupy the spaces between them. However, this elaborate configuration of the Sertoli cells cannot be seen distinctly in routine hematoxylin and eosin (H&E) preparations.