Female Reproductive System

• Female Reproductive System

  Physiology more complex than males, gametes produced but also preparation for developing fetus
• Oogenesis


  • Oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients
  • Primary oocytes develop in primordial follicles that become surrounded by follicle cells
  • Primary oocytes begin meiosis but stall in prophase I
  • Each month a few primary oocytes activated (one will be ovulated)

  
• Ovarian Cycle


  1. Monthly (~28 day) series of events associated with maturation of egg

  2. Follicular phase: period of vesicular follicle growth (days 1–14)

  3. Luteal phase: period of corpus luteum activity (days 14–28)

  4. Only 10–15% women have 28-day cycle (varies)

  
• Stages of Follicle Development


  1. Primordial follicle becomes primary follicle

  2. Primary follicle becomes secondary follicle

  3. Secondary follicle becomes vesicular follicle

  4. Primary oocyte of dominant follicle completes meiosis I, forming secondary oocyte and polar body
• Ovulation


  1. Dominant follicle (when ~2.5 cm) bulges, ovary wall ruptures, oocyte expelled

  2. If not penetrated by sperm, secondary oocyte deteriorates

  3. If penetrated by sperm, second oocyte completes meiosis II, yielding ovum and second polar body

  
• Luteal Phase


  1. After ovulation, antrum fills with clotted blood

  2. Remaining granulosa cells and internal thecal cells enlarge to form corpus luteum

  3. Corpus luteum secretes progesterone and some estrogen

  4. No pregnancy: corpus luteum degrades into corpus albicans (scar) in 10 days

  5. Pregnancy: corpus luteum produces hormones that sustain pregnancy until placenta takes over
• Hormonal Regulation of Ovarian Cycle

  1. GnRH stimulates FSH and LH secretion

  2. FSH and LH stimulate follicles to grow, mature, and secrete sex hormones

  3. Negative feedback inhibits gonadotropin release

  4. Positive feedback stimulates gonadotropin release

  5. LH surge triggers ovulation and formation of corpus luteum

  6. Negative feedback inhibits LH and FSH release
• The Uterine (Menstrual) Cycle

  1. Days 1–5: menstrual phase

  2. Days 6–14: proliferative (preovulatory) phase

  3. Days 15–28: secretory (postovulatory) phase

  
• Estrogen


  • Steroid hormone (formed from testosterone)
  • Promote oogenesis and follicle growth in ovary
  • Exert anabolic effect on female reproductive tract

  
• Effects of Estrogen


  • Support rapid short-lived growth spurts at puberty
  • Induce secondary sex characteristics
  • Maintains low total blood cholesterol and high HDL levels
  • Facilitates calcium uptake
• Progesterone


  • Works with estrogen to establish and regulate uterine cycle
  • Promotes changes in cervical mucus
  • Effects of placental progesterone during pregnancy
  • Inhibits uterine motility
  • Helps prepare breasts for lactation
• Extremely strenuous physical activity can delay/disrupt normal menstrual cycle in girls/women
• Menopause


  Declining estrogen levels cause atrophy of reproductive organs and breasts, irritability and depression, hot flashes, thinning of skin and bone loss, increased total blood cholesterol levels and falling HDL