Figure 17. Hormonal control of male sex differentiation. Wolffian ducts are maintained by testosterone (T) produced by Leydig cells. Müllerian ducts regress under the influence of AMH produced by fetal Sertoli cells, acting through the AMH receptor. The urogenital sinus and external genitalia are virilized by dihydrotestosterone (DHT), resulting from the reduction of testosterone by the enzyme 5α-reductase (not shown). T and DHT act through the same androgen receptor.