1. Control of spermatogenesis:
As shown in the diagram, GNRH is released by the hypothalamus; GNRH stimulates the anteriorpituitary to release FSH and LH. FSH stimulates the seminiferous tubules to produce sperm. LHstimulates the Leydig cells to produce testosterone, the hormone responsible for male secondary sexcharacteristics. These include body hair growth, sex drive, increased muscle mass and certain typesof behaviour, e.g. aggression. Testosterone feeds back on the hypothalamus and controls the amountof GNRH released. Thus, there is a balance in the system. Attempts to modify this system withhormonal contraception has often upset this balance, leading to changes in sex drive (libido).