The hypothalamus sends a releasing hormone (gonadotropin releasing hormone, GNRH) to the anterior pituitary that causes release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates production of sperm. LH stimulates interstitial cells, which lie between the seminiferous tubules, to produce testosterone. Testosterone stimulates and maintains male secondary sexual characteristics, such as growth of body and facial hair, deepening of voice, and general body proportions. Negative feedback maintains constant levels of these hormones.
