Spermatogenesis occurs within the seminiferous tubules of the testis, in close association with the somatic cells of the seminiferous epithelium, the Sertoli cells. At the completion of spermatogenesis, mature spermatids are released from the Sertoli cells into the seminiferous tubule lumen, and proceed through the excurrent duct system, known as the rete testis, until they enter the epididymis via the efferent ducts. The duration of the proliferative period and the number of Sertoli cells produced, together with the subsequent maturation period, determines the spermatogenic potential of the testis, with each Sertoli cell capable of supporting a finite number of germ cells. The endocrine regulation of spermatogenesis is accomplished via a classic negative feedback loop involving interactions between the hypothalamus, pituitary, and testis (the hypothalamic-pituitary-testis, or HPT, axis). The production of spermatozoa is dependent on stimulation by the pituitary gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH), which are secreted in response to hypothalamic gonadotropinreleasing hormone (GnRH).