This page looks at gonad development in terms of endocrine function. Initial gonad differentiation is under the influence of testis-determining factor (TDF) fom the Y chromosome, which will then determine the support cells that will form and secrete the sex steroidal hormones. While gonad reproductive function is not acquired until pubery, the endocrine function of the gonad begins toward the end of the embryonic period when mesenchyme forming the interstitial cells (of Leydig) within the testes secrete testosterone, androstenedione.
Between the end of embryonic (8 weeks) to early fetal (12 weeks) hCG will also stimulate testosterone production. The Sustentacular cells also produce anti-mullerian hormone until puberty.
There are more specific notes on Genital Development
Embryo Images Unit:
Gonads (Covered in Sexual Differentiation) - Endocrine Gonad Notes