Lecture 8: Hormonal Regulation of the Female Reproductive Cycle

Overview

• The female reproductive cycle consists of two main cycles:
  • Ovarian Cycle: Production of the oocyte.
  • Uterine Cycle: Prepares uterus for implantation of fertilized eggs.
• Hormones play a crucial role in regulating these cycles and changes in the breast and cervix.

Ovarian Cycle

• Involves changes in the ovary.
• Gonadotropin-Releasing Hormone (GnRH): Secreted by the hypothalamus.
  • Stimulates release of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
• FSH: Initiates growth of follicles.
  • Follicles secrete estrogen.
• LH: Stimulates ovulation and formation of the corpus luteum.
  • Corpus luteum secretes estrogens, progesterone, relaxin, and inhibin.
  • If fertilization does not occur, it degenerates into scar tissue.

Hormones Involved

• Estrogen: Maintains reproductive organs, increases protein anabolism, develops female secondary sexual characteristics, lowers blood cholesterol.
  • Types: Beta estradiol, estrone, estriol.
• Progesterone: Prepares uterus for implantation, aids mammary glands in milk secretion, inhibits GnRH and LH.
• Relaxin: Facilitates implantation, relaxes uterus, increases pubic symphysis flexibility during labor.
• Inhibin: Inhibits FSH secretion to prevent new follicle development during pregnancy.

Uterine (Menstrual) Cycle

• Stratum Functionalis: Shed if implantation does not occur.
• Phases:
  • Menstrual Phase: Starts with first day of menstruation, tissue sloughs off.
  • Preovulatory Phase: Tissue proliferates in preparation for implantation.
  • Ovulation: Graafian follicle matures and ovulation occurs.
  • Secretory Phase: Post-ovulation, tissue matures; if no implantation, menstruation begins again.

Hormonal Cycle Patterns

• Menstrual Cycle: Typically 28 days.
  • LH: Peaks during ovulation.
  • Estrogen: Peaks around ovulation and before menstruation.
  • Progesterone: Declining levels trigger menstruation.
  • Importance in conception and pregnancy maintenance: Low progesterone can cause issues in maintaining pregnancy.

Additional Notes

• Women's decreased susceptibility to heart disease is linked to estrogen levels, which decline after menopause.
• The corpus luteum degenerates to corpus albicans if fertilization does not occur.
• Hormonal cycles not only influence reproductive tissues but also have systemic effects, such as on muscle and bone strength.