The Role of Ovarian Factors in the Regulation of Metabolism

Abstract

The ovary, or female gonad, plays a central role in the production of the female gametes, the oocytes, and is the major organ where sex steroid hormones are produced in females. In humans, the oocytes are produced from a limiting primordial follicle pool, which is established before birth. From the primordial follicle pool follicles are continuously recruited to develop through primary and secondary stages to become antral follicles. After puberty, when menstrual cycling has commenced, at each cycle, follicles will be recruited from this growing follicle pool under the influence of Follicle Stimulating Hormone (FSH), and ultimately only one of those follicles will reach the preovulatory stage (dominant follicle) (Figure 1). The remaining follicles that are not rescued by FSH will become atretic. Under the influence of Gonadotropin Releasing Hormone (GnRH) from the hypothalamus, Luteinizing Hormone (LH) and FSH are secreted by the pituitary. During a menstrual cycle, which has an average length of 28 days, two phases can be recognized before and after ovulation: the follicular and the luteal phase. In normal cycling women, FSH levels are highest when the dominant follicle emerges. This leads to the production of estrogens by the granulosa cells of the preovulatory follicle. After estrogen levels peak, the LH surge occurs and ovulation will follow. After ovulation, the follicle remnant without the oocyte forms the corpus luteum, which marks the beginning of the luteal phase. The corpus luteum produces progesterone and estrogens which synergistically stimulate the endometrium. When pregnancy does not occur, progesteron and estrogen levels drop and menses start.