Questions

How is female gonadal hormone secretion regulated?

What are the major uses of female sex hormones?

The sex hormones oestrogen (17β-oestradiol, oestrone) and progesterone have important physiological actions in female development, regulation of ovulation and preparation of the female reproductive organ for fertilization and implantation. The secretion of gonadotrophin-releasing hormone (GnRH) from the hypothalamus is pulsatile in nature and under the control of a neural oscillator (or ‘clock’) (Fig. 3.27.1A). This hormone activates cells within the anterior pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which regulate the growth and development of the Graafian follicle in the ovary, stimulate the release of oestrogen from the ovary to induce the proliferation of the endometrium in preparation for implantation, and provide feedback control on the release of gonadotrophins from the anterior pituitary (thus preventing the development of other less mature follicles). As the concentration of oestrogen rises, it exerts a positive feedback on the hypothalamus and pituitary, which promotes a surge in FSH and LH release, thus promoting ovulation (Fig. 3.26.1B). The ruptured follicle develops into the corpus luteum and secretes progesterone, which has negative feedback effects upon FSH release from the anterior pituitary by decreasing the GnRH pulse frequency, which also decreases LH pulse frequency, but the amplitude of the pulses of LH is initially high (i.e. large amount released). Progesterone serves to diminish the proliferative effects of oestrogen upon the endometrium and stimulates differentiation of these cells. Mucus secretion and increased vascularization prepare the uterus for implantation. In the absence of fertilization, the corpus luteum regresses, oestrogen and progesterone levels fall and the endometrium cannot be maintained, resulting in menstruation. The biological activities of these sex hormones are mediated by binding to the steroid receptor family (oestrogen receptor and progestogen receptor).