"The walls of the seminiferous tubules are lined by primitive germ cells and Seoli cells, large, complex glycogen-containing cells that stretch from the basal lamina of the tubule to the lumen. Germ cells must stay in contact with Seoli cells to survive; this contact is maintained by cytoplasmic bridges. Tight junctions between adjacent Seoli cells near the basal lamina form a blood-testis barrier that prevents many large molecules from passing from the interstitial tissue and the pa of the tubule near the basal lamina. Spermatids mature into spermatozoa in deep folds of the cytoplasm of the Seoli cells. Mature spermatozoa are released from the Seoli cells and become free in the lumens of the tubules. The Seoli cells secrete the androgen-binding protein (ABP), inhibin, and MIS. They do not synthesize androgens, but they contain aromatase (CYP19), the enzyme responsible for the conversion of androgens to estrogens, and they can produce estrogens. ABP probably functions to maintain a high, stable supply of androgen in the tubular fluid. Inhibin inhibits follicle-stimulating hormone (FSH) secretion."