Physiology

An androgen, or male sex hormone, is defined as a substance capable of developing and maintaining masculine characteristics in reproductive tissues (notably the genital tract, secondary sexual characteristics, and fertility) and contributing to the anabolic status of somatic tissues.

Testosterone together with its potent metabolite, dihydrotestosterone (DHT), are the principal androgens in the circulation of mature male mammals.

Testosterone is synthesized by an enzymatic sequence of steps from cholesterol within the 500 million Leydig cells located in the interstitial compartment of the testis between the seminiferous tubules, which constitutes approximately 5% of mature testis volume.

The classical biological effects of androgens are primarily mediated by binding to the androgen receptor, a member of the steroid nuclear receptor superfamily encoded by a single gene located on the X chromosome, which then leads to a characteristic patterns of gene expression by regulating the transcription of an array of androgen responsive target genes.

Reference

1. Miller WL, Auchus RJ. The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders. Endocrine Reviews. 2011;32:81–151