Ovarian and Menstrual Cycle

Overview

• Two main events: Menstruation and Ovulation
• Average cycle: 28 days (can vary)
• Menstruation begins on day 1
• Ovulation occurs around day 14

Phases of the Cycle

Follicular Phase

• Covers the first two weeks after menstruation
• Involves the growth of the ovarian follicle (support cells around the egg)

Luteal Phase

• Occurs from day 14 to 28
• Involves the corpus luteum (leftover follicle cells)

Events in the Ovary

• Follicle Stage: The growth of the follicle which supports the egg
  • This is when the follicular phase occurs
• Ovulation: The release of the egg from the ovary
• Corpus Luteum Formation: The leftover follicle becomes the corpus luteum
• Degeneration: Corpus luteum dies unless there's a pregnancy

Events in the Uterus

• Menstrual Flow: Shedding of the endometrium (lining of the uterus)
• Proliferative Phase: Growth and development of the endometrium
• Secretory Phase: Further preparation of endometrium to support a fertilized egg

Hormones Involved

Pituitary Hormones

• FSH (Follicle Stimulating Hormone)
  • Stimulates follicle growth in ovaries
  • Released by pituitary gland
• LH (Luteinizing Hormone)
  • Triggers ovulation
  • Causes formation of corpus luteum
  • Sudden spike around day 14 leads to ovulation

Ovarian Hormones

• Estrogen (Estradiol)
  • Produced by growing follicle
  • Communicates the follicle's readiness to pituitary
• Progesterone
  • Produced by corpus luteum
  • Prepares uterus (endometrium) for potential pregnancy
  • If corpus luteum dies, progesterone declines leading to menstruation

Detailed Cycle Progression

Day 1

• Menstruation begins
• Observable event marks start of the cycle

Follicular Phase

• Pituitary Gland: Releases FSH to grow follicle
• Ovaries: Follicle grows, increasing estrogen production
• Estrogen feedback to pituitary indicating follicle maturity
• Pituitary releases LH for ovulation

Ovulation

• Occurs around day 14
• Egg is released into the fallopian tube

Luteal Phase

• Corpus Luteum Formation: Produces progesterone
• Maintains endometrium for potential pregnancy

End of Cycle

• Without pregnancy, corpus luteum degenerates
• Progesterone stops, menstruation begins again

If Pregnancy Occurs

• Fertilized egg releases hCG (human chorionic gonadotropin)
• hCG signals corpus luteum to continue progesterone production
• Supports embryo growth in endometrium

Conclusion

• Follow hormonal signals and organ responses to understand the cycle
• Consider the cause and effect within each phase
• Diagram flowchart helps visualize processes