Hormones in the Menstrual Cycle

Woman's menstrual cycle is determined by a complex interaction of various hormones. The main hormones involved in the menstrual cycle is a gonadotropin releasing hormone (GnRH), follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. GnRH is secreted by the hypothalamus, FSH and LH are secreted by the anterior pituitary gland, and estrogen and progestin secreted in the ovaries. GnRH stimulates the release of LH and FSH from the anterior pituitary, which in turn stimulates the release of estrogen and progestin from the ovary.

Gonadotropin Releasing Hormone (GnRH)
Gonadotropin releasing hormone (GnRH) released from the hypothalamus that pulsed throughout the menstrual cycle. In order to take the normal menstrual cycle, GnRH must be released in pulses. On average, the frequency of GnRH secretion is once every 90 minutes in the early follicular phase, increasing to once per 60-70 minutes, and decreases with increasing amplitude during the luteal phase. GnRH induces the release of FSH and LH, but LH is much more sensitive to changes in levels of GnRH.

Follicle Stimulating Hormone (FSH)
Follicle stimulating hormone (FSH) secreted by the anterior pituitary gland and is essential for the growth of antral follicles to grow. FSH secretion reaches its peak and most critical during the first week of the follicular phase of the menstrual cycle. FSH induces the secretion of estrogen and progesterone from the ovaries to activate the enzyme aromatase and p450 and exert negative feedback on GnRH secretion. Further FSH-induced granulosa cell proliferation and expression of LH receptors in granulosa cells.

Luteinizing Hormone (LH)
Luteinizing hormone (LH) secreted by the anterior pituitary gland and is necessary for growth and luteinizing preovulatory follicles and ovulation of the dominant follicle. During the follicular phase of the menstrual cycle, LH induces androgen synthesis by theca cells folikuli; stimulate proliferation, differentiation, and secretion folikuli theca cells, and increased LH receptors in granulosa cells. Preovulatory LH surge pushed oocytes did the first meiotic division and initiate cell luteinizing theca and granulosa cells. The corpus luteum is then produced a number of progesterone and estrogen.

Estrogen
Estrogen is produced in the ovaries and is essential for the development and maturation of antral Graafian follicles. Estrogen dominant in the late follicular phase until just before ovulation. Estradiol, the most potent estrogen and abundant, especially coming from androgens produced by theca cells. Androgens migrate from theca cells into granulosa cells, where they are converted to estradiol by the enzyme aromatase. A number of estradiol can also be produced through de novo synthesis by theca cells. Estradiol action including conducting induction FSH receptors on granulosa cells, proliferation and secretion of follicular theca cells, induction of LH receptors in granulosa cells, and proliferation of stromal cells and endometrial epithelium. At the low level circulation, exert estrogen negative feedback on LH and FSH secretion, but at a very high level of estrogen exert a positive feedback on LH and FSH secretion. Estrogen induces further proliferation of granulosa cells and synthesize estrogen converting estrogen receptor, thus creating a positive feedback for herself. In endometrial cycle, estrogen induces proliferation of endometrial glands.

Progestins
Progestin secretion in ovarian follicles mainly by terluteinisasi. Progestin levels rise just before ovulation and peaked five to seven days post-ovulation. The first step in the synthesis of progestins requires p450 enzymes and progestin are two forms of circulating progesterone and progesterone-hydroxy-17. Progestins stimulate the release of proteolytic enzymes from theca cells, which in turn prepares ovulation. Progestins induce further migration from the blood vessels into the follicle wall and stimulates the secretion of prostaglandins in follicular tissue. During the luteal phase, progestin induces enlargement and increased secretion of the endometrium.