Testosterone is a sex hormone produced in the male testes and the adrenal glands of both males and females, and it contributes to a large number of bodily functions. As both men and women produce this hormone, its roles extend beyond the conventional sexual-related functions such as sperm production and libido to tissue growth and brain function.
Testosterone
Testosterone is a steroid hormone derived from the fatty substance cholesterol, which is produced in both men and women, although men produce 10 times more. It has a number of roles in the body, and these can be broadly placed into two categories, those relating to sexual development and those related to anabolism, or tissue growth. Other functions which do not fall into these categories include brain functions related to neuron growth, cognitive ability and mood.
Testosterone Production
Testosterone is produced in the testes of males by cells known as Leydig cells. These respond to chemicals produced by the brain, which signal to increase the number of Leydig cells and to increase the amount of testosterone that they produce. Around 95 percent of circulating testosterone is produced by the testes in men but it is also produced in the adrenal glands. This is also where the majority of circulating testosterone is produced in females. Some is also produced in the female reproductive organs but this is immediately converted to the female sex hormone estrogen. Despite the precursor being the same, that is cholesterol, there are two slightly different synthesis pathways which produce testosterone in the sex organs and the adrenal glands.
Testosterone and Sexual Development
During puberty testosterone is responsible for many of the sexual changes which occur in boys including the production of sperm, the development of facial and bodily hair and the deepening of the voice. The Sertoli cells in the testes produce sperm cells, and this process requires a testosterone signal from the Leydig cells. At about 16 years of age, most teenage boys will have adult levels of testosterone of between 300 and 1200 ng/dL.
Testosterone and Muscle Growth
Testosterone's anabolic functions include muscle and bone growth, and both of these tissues contain testosterone receptors, which detect circulating testosterone. In studies where men have had their testes removed, administering testosterone has been shown to have anabolic effects on muscle. In healthy men there is an acute increase in testosterone levels after high intensity resistance training but what the exact link is between hormonal increases and muscle building is still unclear.
Testosterone and the Brain
Testosterone has also been implicated in certain elements of brain function. A 2003 study in the "Journal of Computational Neuroscience" by Danish researchers Marner and colleagues showed that the average brain mass was larger in males and females. Testosterone has also been linked to superior spatial skills and more risk taking. A 2009 study reported in the "Proceedings of the National Academy of Sciences" by P. Sapienza that women with higher levels of testosterone were more prepared to take risks with regard to their career choices.
Health Risks
Testosterone can be administered by a doctor as a medication for men who are not producing enough testosterone naturally or who have undergone surgery to their testes. Benefits of this kind of therapy can include and increased libido, sexual function, cognitive ability, muscle mass and bone density. There are concerns, however, that exogenous testosterone may increase your risk of developing prostate cancer, although no conclusive evidence exists to support this. Other concerns include worsening severe heart conditions, altering blood composition to make it more viscous and toxicity to the liver. If you are concerned about your testosterone levels, consult your doctor.
