Figure 1.

A schematic representation of the components of the hypothalamic-pituitary-testicular axis and the endocrine regulation of spermatogenesis. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are secreted by the pituitary in response to hypothalamic gonadotropin releasing hormone (GnRH). Whereas FSH acts directly on the germinal epithelium, LH stimulates the secretion of testosterone from Leydig cells. Testosterone stimulates sperm production and also feeds back to the hypothalamus and pituitary to regulate GnRH secretion. FSH stimulates Sertoli cells to support spermatogenesis and secrete inhibin B, which negatively regulates FSH secretion.