In-Depth Notes on Female Sexual and Reproductive Cycles

Reproductive and Sexual Cycles of Females

  • Reproductive Cycle: A sequence of events from fertilization to giving birth and returning to fertility.
  • Sexual Cycle: Events that recur every month when there is no pregnancy, consisting of:
    • Ovarian Cycle: Events in the ovaries.
    • Menstrual Cycle: Parallel changes in the uterus controlled by hormonal fluctuations.

Oogenesis

  • Oogenesis: The process of egg production; produces haploid gametes through meiosis.
  • Characteristics of Oogenesis:
    • Cyclic event, releasing one egg each month.
    • Accompanied by cyclic changes in hormone secretion and histological structure of ovaries/uterus.
    • Monthly menstrual flow results from uterine changes.
    • By puberty, around 200,000 oocytes remain (lifetime supply) but only about 480 ovulations occur.

Female Sexual Cycle

  • Averages 28 days, but can vary from 20 to 45 days.
  • Hormonal Regulation:
    • Hierarchical control: Hypothalamus → Pituitary → Ovaries → Uterus.
    • Hypothalamus regulates the pituitary gland, which in turn regulates the ovaries.
    • Ovaries secrete hormones that regulate the uterus and exert feedback control over the hypothalamus and pituitary.

Phases of the Sexual Cycle

  1. Follicular Phase: First two weeks, includes menstruation (Day 1-3 to 5).
    • Uterus replaces lost tissue by mitosis; follicles grow.
  2. Ovulation: Occurs around Day 14.
    • The remainder of the follicle becomes corpus luteum.
  3. Luteal Phase: Last two weeks where the corpus luteum stimulates endometrial secretion and thickening.
    • If pregnancy does not occur, endometrium breaks down in the last 2 days, leading to menstruation.

The Ovarian Cycle

  • Three stages:
    1. Follicular Phase (Days 1-14):
    • Most variable phase of the cycle; difficult to predict ovulation.
    • FSH stimulates follicle growth and estradiol secretion.
    • Dominant follicle develops, leading to ovulation.
    1. Ovulation:
    • Typically occurs around Day 14; involves the rupture of the mature follicle, releasing the egg.
    • Triggered by a surge in LH and a spike in FSH, leading to secondary oocyte formation.
    1. Luteal Phase (Days 15-28):
    • Corpus luteum forms and secretes progesterone.
    • If pregnancy does not occur, the luteum degenerates.

Signs of Ovulation

  • Helpful for couples trying to conceive:
    • Thinner, stretchier cervical mucus.
    • Basal body temperature increases by 0.4° to 0.6°F post-ovulation.
    • Possible presence of Mittelschmerz: twinges of pain at ovulation.
    • Optimal conception occurs within 24 hours of these signs.

The Menstrual Cycle

  • Four phases:
    1. Menstrual Phase: Vaginal discharge of blood and fluid, average duration is 5 days, starting from Day 1 of the new cycle.
    • Women expel about 40 mL blood and 35 mL serous fluid.
    1. Proliferative Phase: Rebuilding functional endometrium lost in menstruation, stimulated by estrogen. Ends around Day 14 with the endometrium at 2-3 mm thickness.
    2. Secretory Phase (Days 15-26): Endometrial thickening due to progesterone effects, making it suitable for potential embryonic development.
    3. Premenstrual Phase: Last 2 days before menstruation, characterized by degeneration of the endometrium and the onset of menstrual fluid.

Endometriosis

  • A condition involving the growth of endometrial tissue outside the uterus, typically resulting in:
    • Pain and potential infertility.
    • Prevalence of 6% to 10% among women, often thought to occur due to retrograde menstruation.

Excitement and Plateau Phases of Sexual Response

  • Excitement Phase: Labia minora engorge with blood; vaginal transudate moistens and lubricates.

Orgasm Phase

  • Involuntary contractions occur, with sensations spreading from the clitoris through the pelvis, followed by pelvic contractions about 0.8 seconds apart.
  • Women do not experience a refractory period and can sometimes have multiple orgasms.