Hypothalamic-Pituitary Axis (Female)

Overview

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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