Updated: 4/13/2019

Hypothalamic-Pituitary Axis (Female)

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Overview

female hypo pit axis

  • Overview
    • hypothalamic-pituitary axis controls 2 functions of ovaries
      • oogenesis
      • synthesis and secretion of female sex steroid hormones
        • progesterone and 17β-estradiol (estrogen)
  • 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
      • follicular phase of menstrual cycle
        • LH
          • aka luteinizing hormone
          • LH → (+) theca cells → ↑ progesterone and androstenedione
            • LH acts on theca cells
              • increases activity of cholesterol desmolase 
                • increases synthesis/secretion of progesterone
                • increases synthesis/secretion of androstenedione
                  • androstenedione diffuses from theca cells to granulosa cells
        • FSH
          • aka follicle-stimulating hormone
          • FSH → (+) granulosa cells → ↑ 17β-estradiol
            • FSH acts on granulosa cells 
              • increases activity of aromatase
                • increases synthesis/secretion of 17β-estradiol
              • androstenedione diffuses from theca cells to granulosa cells
                • granulosa cells express 17β-hydroxysteroid dehydrogenase
                  • catalyzes conversion of androstenedione to testosterone
                • granulosa cells express aromatase
                  • catalyzes conversion of testosterone to 17β-estradiol
        • negative feedback
          • 17β-estradiol (via granulosa cells)
            • ↑ 17β-estradiol → (-) hypothalamus → ↓ GnRH
              • 17β-estradiol acts on hypothalamus
                • downregulates GnRH secretion
            • ↑ 17β-estradiol → (-) anterior pituitary → ↓ FSH and ↓ LH
              • 17β-estradiol acts on anterior lobe of pituitary
                • downregulates LH and FSH secretion
      • midpoint of menstrual cycle (ovulation)
        • positive feedback
          • 17β-estradiol (via granulosa cells)
            • ↑↑ 17β-estradiol → (+) hypothalamus → ↑ GnRH
              • 17β-estradiol acts on hypothalamus
                • upregulates GnRH secretion
            • ↑↑ 17β-estradiol → (+) anterior pituitary → ↑↑ FSH, ↑↑ LH
              • 17β-estradiol acts on anterior lobe of pituitary
                • upregulates LH, FSH secretion
      • luteal phase of menstrual cycle
        • LH surge
          • ↑↑ LH → (+) corpus luteum → ↑ progesterone
            • LH acts on corpus luteum
              • increases synthesis/secretion of progesterone
        • negative feedback
          • progesterone (via granulosa lutein cells and theca lutein cells)
            • ↑ progesterone → (-) hypothalamus → ↓ GnRH
              • progesterone acts on hypothalamus
                • downregulates GnRH secretion
            • ↑ progesterone → (-) anterior pituitary → ↓ FSH and ↓ LH
              • progesterone acts on anterior lobe of pituitary
                • downregulates LH and FSH secretion
 

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