| Popis: |
Normal male genital differentiation requires fetal testicular secretion of both testosterone and the nonsteroidal müllerian-inhibitory factor. It appears that secretion of testosterone, at least during the critical period of differentiation, occurs in response to stimulation by CG, although pituitary LG may influence Leydig cell function in later fetal life. To date, there is no evidence to support a similar endocrine function for the fetal ovary in female genital differentiation. In both sexes normal fetal pituitary gonadotropin secretion appears to be required for maturation of the germ cells and related elements. The pattern of FSH and LH secretion in the fetus reflects gradual maturation of a functional hypothalamo-pituitary unit responsive to feedback inhibition by sex steroids. The higher levels of gonadotropins in female fetuses from from 12--20 weeks suggest either that this maturation occurs earlier in males than in females, or, more probably, that feedback recognition of androgens is established before gestation reflects development of an estrogen-mediated feedback mechanism, and in addition the possible influence that hormones, such as prolactin or placental estradiol, may have on testicular steroidogenesis. |
