Biosynthesis
Testosterone is a steroid hormone, which means that it is made by the body from cholesterol. The cholesterol can either be made by the liver or come from the diet. Testosterone synthesis can follow one of two pathways, both of which are regulated by special proteins called enzymes.
The physiology department at the Second Medical School of Czechoslovakia notes that cholesterol can either be turned into progenolone or progesterone (which is also a steroid hormone); both of these intermediates can be turned into androstenedione, which can be used to make testosterone.
Tissue Production
Testosterone is an androgen, which means that it helps produce secondary sex characteristics. As Endotext.org explains, testosterone is the dominant androgen in males. It is responsible for the development of pubic hair and for the onset of puberty. Testosterone is primarily produced by specialized cells within the testes called Leydig cells. In women, testosterone is produced in small amounts by the ovaries. The adrenal glands (in both men and women) are able to produce testosterone as well, but this androgen production is usually insignificant.
Regulation
Production of testosterone is controlled by the anterior pituitary. The pituitary gland represents an intersection of the nervous system and the endocrine system and allows for neural control of hormone levels. The anterior pituitary is able to secrete two different hormones that can increase testosterone production: luteinizing hormone and follicle stimulating hormone. As Endotext.org explains, these two hormones drive testosterone synthesis by increasing the rate at which cholesterol is made into progenolone and progesterone. This is known as a rate-limiting step, because once those two molecules are made then testosterone production occurs fairly rapidly.
