What is testosterone?

Testosterone is a hormone secreted by the testicle. It is under regulatory control of other hormones in the body. The hypothalamus in the front of the brain secretes GnRH. Stimulated by this the pituitary gland at the base of the brain secretes FSH and LH. In response to LH stimulation the testicle secretes testosterone. When testosterone levels rise the pituitary and hypothalamus lower GnRH and FSH/LH production, thus lowering the signal to produce testosterone. With all of this in balance the testosterone level varies over the course of the day within a normal range. In adults testosterone has a dozen or more functions. It is needed for sperm development, is involved in mood and energy levels, helps maintain muscle activity, and affects libido.