Human androgens have a wide range of functions from birth to death. These steroids are essential to life and function as we have come to understand it. They are also abused extensively because of their virilizing effect and other body image enhancing properties. They have been banned in competitive sports but continue to be used widely.
Androgens are a powerful subset to steroids which are used extensively in medicine and abused by many sports enthusiasts and body builders. Androgens include adrenal androgens (produced by the adrenal glands) and all of the 19-carbon steroids synthesized by the adrenal cortex and the zonula retucularis i.e. the innermost region of the adrenal cortex.
Types of Androgens:
Testosterone is the main androgen however there are other androgens. Some of these are mentioned below:
This steroid hormone is produced from cholesterol in the adrenal cortex. It is the natural precursor of natural estrogens. DHEA is also known as dehydroisoandrosterone and dehydroandrosterone.
An androgenic steroid
Androstenedione, sometimes called Andro is produced in the testicles, adrenal cortex and ovaries. Androstenedione is converted metabolically to testosterone and other androgens. The usage of androstenedione for body building purposes is illegal internationally.
is the steroid precursor which is believed to be the main regulator of gonadotrophin secretion in mammals.
is a chemical by-product produced by the lysis of androgens. It is also derived from progesterone. It has masculinising effect but these effects are only about one-seventh the intensity of testosterone in the human body. It can be detected easily by testing the urine and / or blood of both male and female clients.
DHT is a metabolite of testosterone. It is one of the most potent androgens. It is more potent than testosterone and is produced by the adrenal cortex. This androgen can be synthesized in the laboratory.
Functions of Androgens:
Androgens play a key role in the formation of the testicles.
During the embryonic stage of human development, the gonads are at first capable of becoming either ovaries (female sex organs) testis (male sex organs). In humans, at about the age of four weeks gonadal rudiments appear in the intermediate mesoderm immediately next to the kidneys. During weeks five and six epithelial sex cords appear within the forming testes and incorporate the germ cells as they migrate into the gonads. In male embryos specific chromosome genes regulate and control the development of the male phenotype. SRY genes are most important for this development to occur. Androgen exposure is responsible for the conversion of the early bipotential gonad into testes. In males, the sex cords fully invade the developing gonads.
Evolution of Leydig Cells and Androgen Production
During the embryonic stage mesoderm-derived epithelial cells of the sex cords develop in the testes and later become the Sertoli cells. Sertoli cells later function to support sperm cell formation. During weeks seven to nine a small amount of non-epithelial cells appear between the tubules, during fetal development. These become the Leydig cells. After appropriate differentiation and maturation the Leydig cells begin to produce androgens.
Effects of Androgens
During embryonic development androgens function as pancrean hormones. These hormones are required by the Sertoli cells in order to facilitate sperm production. Androgens are also required for masculinization of the developing male fetus, including penis and scrotum formation – this process will be discussed in more detail in another article.
Embryological stages in human development.
The mesonephros is an excretory organ of the embryo. Under the influence of androgens, parts of the mesonephron and the wolffian ducts develop into male sex organs viz. the epididymis, the vas deferens and the seminal vesicles. This powerful action of mammalian androgens is supported by AMH hormone which is secreted by Sertoli cells. The key function AMH is to prevent embryonic Müllerian ducts from developing into fallopian tubes and other female reproductive tract tissues in male embryos. AMH and androgens cooperate to allow for the normal movement of testes into the scrotum.
Early Hormonal regulation
In humans Androgen action on target tissues involves conversion of testosterone to 5α-dihydrotestosterone. This is called dihydrotestosterone (DHT). In week 11 to week 12 of embryonic development human chorionic gonadotrophin (hCG) promotes the differentiation and specialization of Leydig cells and the intrinsic production of androgens. These processes take place before the production of the pituitary hormone called Luteinizing Hormone (LH).