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9.4 - Hormonal Regulation of the Reproductive System

9.4 Hormonal Regulation of the Reproductive System

Key Definitions

  • Gonad: Organ that produces reproductive cells (gametes); the ovary produces eggs (ova) and the testes produce sperm.

  • Sex hormone: Chemical compounds that control the development and function of the reproductive system or secondary sex characteristics.

Male Reproductive System

  • Key Organs:

    • Testes: Produce sperm and testosterone.

    • Epididymis: Stores sperm until maturation.

    • Ductus deferens: Transports sperm.

    • Seminal vesicle, prostate gland, Cowper's gland: Contribute fluids to semen.

    • Penis: Organ for copulation.

    • Scrotum: Pouch containing testes, regulates temperature.

Hormonal Processes in Males

  • Puberty begins with:

    • Increase in gonadotropin-releasing hormone (GnRH) from the hypothalamus.

    • GnRH stimulates the anterior pituitary to release:

      • Follicle-stimulating hormone (FSH): Promotes sperm production in testes.

      • Luteinizing hormone (LH): Stimulates testosterone release, functioning to develop sex organs and secondary sexual characteristics.

  • Negative Feedback Mechanism:

    • Testosterone and inhibin are produced by interstitial cells and seminiferous tubules, respectively, inhibiting further release of GnRH, LH, and FSH when levels are sufficient.

Andropause

  • Gradual decline in testosterone levels in men starting around age 40.

    • Symptoms include:

      • Fatigue

      • Depression

      • Loss of muscle and bone mass

      • Decrease in sperm production (not complete cessation).

Female Reproductive System

  • Key Organs:

    • Ovary: Produces eggs and hormones.

    • Oviduct (Fallopian tube): Transports eggs to the uterus.

    • Uterus: Site of implantation and fetal development.

    • Vagina: Birth canal and copulatory organ.

Hormonal Processes in Females

  • Puberty begins similarly:

    • Increase in GnRH from the hypothalamus leads to:

      • Release of LH and FSH from the anterior pituitary.

    • FSH and LH stimulate:

      • Ovaries to produce estrogen and progesterone, which develop female secondary sex characteristics and start the menstrual cycle.

The Menstrual Cycle

  • Comprised of two cycles:

    • Ovarian Cycle: Takes place in ovaries with two stages - follicular and luteal.

    • Uterine Cycle: Takes place in the uterus.

Ovarian Cycle

  • Follicular Stage:

    • FSH stimulates maturation of follicles.

    • Follicle produces estrogen which inhibits further FSH release and triggers an LH surge.

    • Surge in LH causes ovulation (release of ovum).

  • Luteal Stage:

    • Post-ovulation, the ruptured follicle develops into the corpus luteum, which secretes progesterone and some estrogen.

    • High levels of these hormones inhibit FSH and LH production.

    • Corpus luteum degenerates if no fertilization occurs, dropping estrogen and progesterone levels, thus prompting the anterior pituitary to restart the cycle.

Uterine Cycle

  • Starts on first day of menstruation (around 5 days).

  • Uterine lining (endometrium) thins during menstruation.

  • Estrogen levels rise post-menstruation, causing thickening of the endometrium around day 6.

  • Progesterone peaks around day 14 leading to further thickening.

  • If fertilization does not occur, hormone levels drop, resulting in menstruation.

Menopause

  • Decline in estrogen and progesterone leads to cessation of menstrual cycles, occurring typically around age 50.