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Updated: Nov 9 2022

Hypothalamic-Pituitary Axis (Male)

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https://upload.medbullets.com/topic/116009/images/regulationofspermatogenesis.jpg
https://upload.medbullets.com/topic/116009/images/male repro regulation.jpg
  • Overview
    • Overview
      • hypothalamic-pituitary axis controls 2 functions of testes
        • spermatogenesis
        • synthesis and secretion of male sex steroid hormones
          • testosterone
    • Hypothalamic-pituitary axis
      • hypothalamus
        • GnRH
          • aka gonadotropin-releasing hormone
          • pulsatile GnRH secretion via preoptic nucleus of hypothalamus
            • GnRH travels in hypothalamic-hypophyseal portal blood system
            • GnRH acts on gonadotrophs in anterior lobe of pituitary
              • GnRH → ↑ FSH and LH (pulsatile)
      • pituitary
        • LH
          • aka luteinizing horome
          • LH → (+) Leydig (interstitial) cells → ↑ testosterone
            • LH acts on Leydig cells
              • increases activity of cholesterol desmolase enzyme
                • increases synthesis and secretion of testosterone via cholesterol
                  • testosterone has local (paracrine) and distal (endocrine) effects
                    • locally, testosterone acts on Sertoli cells
                      • reinforces pro-spermatogenesis action of Sertoli cells
        • FSH
          • aka follicle-stimulating hormone
          • FSH → (+) Sertoli (sustentacular) cells → (+) spermatogenesis
            • FSH acts on Sertoli cells
              • increases synthesis and secretion of androgen-binding protein (ABP)
                • Sertoli cells secrete ABP into luminal space of seminiferous tubule, near developing spermatogonia
                • ABP binds testosterone and maintains high local testosterone levels
              • increases synthesis of growth factors and other products that supports developing spermatogonia and supports spermatogenesis
              • increases synthesis and secretion of inhibin
                • inhibin provides negative feedback of hypothalamic-pituitary axis
                • low inhibin levels are asociated with high levels of FSH
    • Negative feedback
      • testosterone (via Leydig cells)
        • testosterone acts on hypothalamus
          • inhibits GnRH secretion
        • testosterone acts on anterior lobe of pituitary
          • inhibits LH and FSH secretion
      • inhibin (via Sertoli cells)
        • inhibin acts on anterior lobe of pituitary
          • inhibits FSH secretion
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