Androgen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. This includes the activity of the accessory male sex organs and development of male secondary sex characteristics. Androgens, which were first discovered in 1936, are also called androgenic hormones or testoids. Androgens are also the original anabolic steroids. They are also the precursor of all estrogens, the female sex hormones. The primary and most well-known androgen is testosterone. Androgen ablation can be used as an effective therapy in certain urologic cancers such as metastatic prostate cancer.

Types of androgens

thumb|right|450px|Steroidogenesis, showing the relation between several androgens at bottom left. (Estrone and estradiol, in contrast, are estrogens. A subset of androgens, adrenal androgens, includes any of the 19-carbon steroids synthesized by the adrenal cortex, the outer portion of the adrenal gland (zonula reticularis - innermost region of the adrenal cortex), that function as weak steroids or steroid precursors, including dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEA-S), and androstenedione.

Besides testosterone, other androgens include:

• Dehydroepiandrosterone (DHEA): a steroid hormone produced in the adrenal cortex from cholesterol. It is the primary precursor of natural estrogens. DHEA is also called dehydroisoandrosterone or dehydroandrosterone.

• Androstenedione (Andro): an androgenic steroid produced by the testes, adrenal cortex, and ovaries. While androstenediones are converted metabolically to testosterone and other androgens, they are also the parent structure of estrone. Use of androstenedione as an athletic or body building supplement has been banned by the International Olympic Committee as well as other sporting organizations.

• Androstenediol: the steroid metabolite that is thought to act as the main regulator of gonadotropin secretion.

• Androsterone: a chemical by-product created during the breakdown of androgens, or derived from progesterone, that also exerts minor masculinising effects, but with one-seventh the intensity of testosterone. It is found in approximately equal amounts in the plasma and urine of both males and females.

• Dihydrotestosterone (DHT): a metabolite of testosterone, and a more potent androgen than testosterone in that it binds more strongly to androgen receptors. It is produced in the adrenal cortex.

Testes formation

During mammalian development, the gonads are at first capable of becoming either ovaries or testes. In humans, starting at about week 4 the gonadal rudiments are present within the intermediate mesoderm adjacent to the developing kidneys. At about week 6, epithelial sex cords develop within the forming testes and incorporate the germ cells as they migrate into the gonads. In males, certain Y chromosome genes, particularly SRY, control development of the male phenotype, including conversion of the early bipotential gonad into testes. In males, the sex cords fully invade the developing gonads.