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27 . The Male Reproductive System: Hormonal Regulation. Male Reproductive System – Hormonal Regulation. Hormonal Regulation of Male Reproductive Function – pp. 1038 – 1040 . Hormonal Regulation of Male Reproductive Function.

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  1. 27 The Male Reproductive System: Hormonal Regulation

  2. Male Reproductive System – Hormonal Regulation • Hormonal Regulation of Male Reproductive Function – pp. 1038 – 1040

  3. Hormonal Regulation of Male Reproductive Function • A sequence of hormonal regulatory events involving the hypothalamus, anterior pituitary gland, and the testes • The hypothalamic-pituitary-gonadal (HPG) axis

  4. HPG Axis • Hypothalamus releases gonadotropin-releasing hormone (GnRH) • GnRH stimulates the anterior pituitary to secrete FSH and LH • FSH causes sustentacular cells to release androgen-binding protein (ABP), which makes spermatogenic cell receptive to testosterone • LH stimulates interstitial cells to release testosterone

  5. HPG Axis • Testosterone is the final trigger for spermatogenesis • Feedback inhibition on the hypothalamus and pituitary results from • Rising levels of testosterone • Inhibin (released when sperm count is high)

  6. 1 GnRH Anterior pituitary Via portal blood 8 7 2 Inhibin 2 LH FSH Interstitial cells 4 3 6 Testosterone Somatic and psychological effects at other body sites Sustentacular cell Spermatogenic cells 5 Seminiferous tubule Stimulates Inhibits Figure 27.9

  7. Mechanism and Effects of Testosterone Activity • Testosterone • Synthesized from cholesterol • Transformed to exert its effects on some target cells • Dihydrotestosterone (DHT) in the prostate • Estrogen in some neurons in the brain

  8. Mechanism and Effects of Testosterone Activity • Prompts spermatogenesis • Targets all accessory organs; deficiency leads to atrophy • Has multiple anabolic effects throughout the body • Is the basis of the sex drive (libido) in males

  9. Male Secondary Sex Characteristics • Features induced in the nonreproductive organs by male sex hormones (mainly testosterone) • Appearance of pubic, axillary, and facial hair • Enhanced growth of the chest and deepening of the voice • Skin thickens and becomes oily • Bones grow and increase in density • Skeletal muscles increase in size and mass

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