Development of the male reproductive system

Male and female reproductive systems develop in close relation to the urinary tract. Until approximately 7 weeks gestation, the human embryo remains sexually bipotential. Subsequently, in males, testis-inducing factors cause differentiation from the default female phenotype. As the testis forms, testosterone and other androgens drive the formation of the external genitalia and internal male reproductive structures, while other testicular factors cause regression of female reproductive organ precursors. Androgens also play a role in the descent of the testicles from their origin in the upper abdomen. Germ cells enter an arrested phase of maturation in the fi rst trimester. A surge of testosterone in the neonatal period plays a role in testicular development, but it is not until the largest androgen surge of puberty that gonadarche occurs with the onset of spermatogenesis. In this chapter, we review the formation and maturation of the reproductive system, with an emphasis on hormonal factors and aspects relevant to clinical care of male reproductive patients.