By about 8 weeks after conception the sex hormones begin to play an important role in sex differentiation. The two duct systems shown in Figure 5.2a—the Wolffian ducts and the Mullerian ducts—begin to differentiate into those internal structures shown in Figure 5.2b. In a male fetus, androgens secreted by the testes stimulate the Wolffian ducts to develop into the vas deferens, seminal vesicles, and ejaculatory ducts. Another substance released by the testes is known as Mullerian-inhibiting substance (MIS). MIS causes the Mullerian duct system to shrink and disappear in males (Wilhelm et al., 2007). In the absence of androgens the fetus develops female structures (Clarnette et al., 1997). The Mullerian ducts develop into the fallopian tubes, the uterus, and the inner third of the vagina, and the Wolffian duct system degenerates.
Gender Issues