Female Reproductive Physiology

Female Reproductive Physiology

• The female gonads are the ovaries, which, along with the uterus and fallopian tubes, constitute the female reproductive tract.
• Ovaries function in oogenesis and secrete female sex hormones (progesterone and estrogen)
• The ovary is comprised of three zones:
  • Cortex: outer, largest zone, containing oocytes within follicles, responsible for steroid hormone synthesis.
  • Medulla: middle zone, a mix of cell types.
  • Hilum: inner zone, where blood vessels and lymphatics pass.
• The single functional unit of the ovaries is the ovarian follicle, which supports the developing oocyte and plays a crucial role in ovulation, fertilization, and pregnancy maintenance.
• Oogenesis:
  • Primordial germ cells in the developing ovaries produce oogonia by mitosis until weeks 20-24.
  • From weeks 8-9, some oogonia enter meiosis I to form primary oocytes, which remain in prophase I until ovulation.
  • At birth, around 2 million oocytes remain; by puberty, only 400,000 are left.
• Follicle Development:
  • Occurs in stages (illustrated in Figure 10.7 and 82-3):
  • Primordial follicle to primary follicle lasting years (13-50 years).
  • Primary follicle to secondary follicle (70-85 days).
  • Secondary follicle to Graafian follicle (48 hours).
  • Graafian follicle undergoes ovulation, releasing the secondary oocyte.
  • The corpus luteum forms from the residual follicle if fertilization does not occur, degenerating into the corpus albicans.
• Ovarian Follicle Development Stages:
  • First stage is similar to the oocyte’s prophase I stage.
  • Second stage lasts 70-85 days, where fluid containing steroid hormones, mucopolysaccharides, proteins, and FSH builds up in a central area called the antrum.
  • Follicle transforms into a graafian follicle, of 2-5mm average diameter.
• Ovarian Steroid Hormone Synthesis and Secretion:
  • Ovaries synthesize progesterone and estradiol.
  • Theca cells synthesize progesterone.
  • Theca cells generate androstenedione, converted to testosterone, then estradiol in the granulosa cells via aromatase enzyme, utilizing LH and FSH.
• Regulation of Ovaries:
  • Highly controlled by the hypothalamic-pituitary axis.
  • GnRH from hypothalamus stimulates FSH & LH release.
  • FSH & LH target the ovaries to stimulate follicular development, ovulation and sex hormone synthesis.
  • Negative feedback mechanisms involve estradiol and progesterone, with varying effects across different phases of the cycle.
• Phases of the Menstrual Cycle:
  • Follicular (proliferative):
    • 14 days prior to ovulation
    • Dominated by estrogen
    • Prepares the endometrium for potential implantation.
  • Ovulation:
    • Day 14 of a typical 28 day cycle
    • Triggered by an LH surge, causing the dominant follicle to rupture and release the secondary oocyte.
  • Luteal (secretory):
    • 14 days after ovulation.
    • Dominated by progesterone.
    • Prepares the endometrium for pregnancy.
    • If fertilization does not occur, the corpus luteum degenerates.
  • Menses:
    • End of cycle.
    • Sloughing of the endometrial lining if no pregnancy occurs.
    • Prepares the uterine lining for a new cycle.
• Actions of Estrogen and Progesterone:
  • Affect various target tissues, including the breasts, uterus and fallopian tubes.
  • Usually work in a complementary fashion to support reproductive processes.