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Male Reproductive Hormones Flashcards

  • Overview of Hormonal Regulation in Males

    • The process of male reproductive function is facilitated by a series of hormones that follow a sequence starting from the hypothalamus.

  • Key Structure Components

    • Hypothalamus: Produces Gonadotropin-Releasing Hormone (GnRH)
    • Anterior Pituitary: Responds to GnRH by releasing
    • Follicle-Stimulating Hormone (FSH)
    • Luteinizing Hormone (LH)

  • Hormonal Steps

    • Step 1: Hypothalamus releases GnRH.
    • Step 2: GnRH targets anterior pituitary to trigger the release of FSH and LH.
    • Step 3: simultaneous action:
    • 3a: FSH stimulates Sertoli cells (or sustentacular cells) in the seminiferous tubules.
      • Concept: Sertoli cells nurture developing sperm and produce Androgen Binding Protein (ABP).
      • Role of ABP: Increases testosterone concentration near Sertoli cells, enhancing spermatogenesis.
    • 3b: LH stimulates interstitial cells (Leydig cells) in the testes to produce testosterone.

  • Role of Testosterone

    • Promotes spermatogenesis directly.
    • Responsible for male secondary sex characteristics (e.g., increased body hair, deepening voice due to enlarged larynx, muscle mass gain).
    • Testosterone also contributes to metabolic rate increases due to muscle and skeleton changes.

  • Feedback Mechanisms

    • Rising testosterone levels provide negative feedback to the hypothalamus, reducing GnRH secretion.
    • Inhibin produced by Sertoli cells also contributes to feedback, inhibiting both GnRH and FSH production
    • Effect of Feedback: Prevents overproduction of testosterone and sperm; maintains hormonal balance.

  • Inhibin

    • A hormone produced by Sertoli cells that decreases the release of GnRH and FSH.
    • Functions to regulate spermatogenesis by controlling FSH levels.

  • Testosterone Levels

    • Varies significantly throughout life:
    • Pre-birth: Male fetus levels are ~66% of adult levels.
    • Post-birth: Levels drop significantly then rise during puberty, stabilizing into adulthood.
    • Decline in later life, reflecting decrease towards levels seen pre-birth.

  • Development of Secondary Sex Characteristics

    • Changes include:
    • Hair growth (facial, chest, armpits, pubic).
    • Voice deepening due to larynx enlargement.
    • Increased muscle mass and strength
    • Enhanced metabolic rate and temperature regulation.

  • Conclusion

    • Understanding hormonal regulation is crucial for grasping male reproductive physiology and the effects of hormones like testosterone on physical development.