Pregnancy Child Birth

The Three Female Reproductive Cycles

Dec 18 2007

The cyclic menstrual period is the most obvious manifestation of the reproductive cycle in women. In fact, the female reproductive cycle consists of three interrelated cycles, working in exquisite concert with each other to create the conditions necessary for fertilization and implantation. We will call these the hormonal cycle, the uterine or endometrial cycle, and the ovarian cycle. The hormonal cycle is the secretion, in precise order and with perfect timing, of the chemical messengers or hormones necessary to control the entire female reproductive process. The uterine or endometrial cycle is the preparation each month of the endometrium, the lining of the uterus for possible implantation of a fertilized egg. Without a fertilized egg, the endometrium is shed, to build up again in the next cycle. The ovarian cycle refers to the monthly development and expulsion of the egg cell from the ovary to the fallopian tube, where it meets the sperm, or, without a fertilization encounter, disintegrates.

Female Reproductive Hormones

• Hypothalamic Hormones
• Gonadotropin Releasing Hormone (GnRH)
• Pituitary Hormones
• Follicle-stimulating Hormone (FSH)
• Luteinizing Hormone (LH)
• Prolactin
• Estrogen
• Ovarian Hormones
• Progesterone Androgens
• Folticutostatin (Inhibin)

The Feedback Mechanism and Ovulation

Low levels of estrogen in the early part of your menstrual cycle stimulate the manufacture of the gonadotropins, FSH and LH.

Higher levels of estrogen, in the midportion of the cycle, suppress FSH. FSH stimulates the secretion of inhibin (folliculostatin), and in turn, inhibin suppresses the secretion of FSH.

After ovulation, high levels of progesterone inhibit the secretion of both gonadotropins from the pituitary by inhibiting GnRH secretion in the hypothalamus. If gonadotropins remained high, the ovarian follicles would be subjected to constant stimulation meaning that ovulation could occur at any time. Instead, the exquisite timing of the feedback mechanisms provides for ovulation only once each cycle.

Tags:androgens, female reproductive cycle, fertilized egg, gonadotropins, hormonal cycle, hypothalamic hormones, luteinizing hormone, ovarian cycle, ovarian follicles, ovulation, pituitary hormones pregnancy