Final answer:
Testosterone is the major androgen produced by the interstitial cells of the testes that stimulates male development. It is secreted by Leydig cells, located between the seminiferous tubules. Testosterone plays a role in the anatomical differentiation of male sexual organs and activates physical changes during puberty.
Step-by-step explanation:
Testosterone, an androgen, is a steroid hormone produced by Leydig cells. The alternate term for Leydig cells, interstitial cells, reflects their location between the seminiferous tubules in the testes. In male embryos, testosterone is secreted by Leydig cells by the seventh week of development, with peak concentrations reached in the second trimester. This early release of testosterone results in the anatomical differentiation of the male sexual organs. In childhood, testosterone concentrations are low. They increase during puberty, activating characteristic physical changes and initiating spermatogenesis.