The Female Reproductive System - 1 Hypothalamus-Pituitary-Gonad Axis and Follicle Maturation Jennifer Carbrey Ph.D. Department of Cell Biology Common Axis once each cycle an increase in estrogen causes an increase in GnRH production (and progesterone) In males & females, GnRH secretion is pulsatile. Local secretion of testosterone is needed for development of ovum (female) and of sperm (male). Inhibin B decreases FSH secretion. Sex hormones regulate GnRH, LH and FSH. image by Uwe Gille (modified), http://commons.wikimedia.org/wiki/File:Hypothalamus-Hypophysis-Testicle-Hormone-Axis_%28engl.%29.svg, Creative Commons Attribution-Share Alike 3.0 Unported license The Roles of the Ovary Oocyte Number Germ cells (oocytes) are generated in embryogenesis (10-20 milllion per ovary at birth). 400-500 oocytes actually mature to ovulation. Oocyte Maturation oocyte granulosa cells theca cells LH FSH Theca cells Granulosa cells Estrogen increases the number of LH receptors -positive feedback produce convert As follicle matures, the follicle produces more and more estrogen testosterone testosterone In addition, the number of LH and FSH receptors increases, making the follicle to estrogen more sensitive to their effects Image modified from Cambridge Natural History, Volume X, Mammalia (1902), by Frank E. Beddard, Macmillan & Co., Limited, public domain Ovulation image by Uwe Gille (modified), http://commons.wikimedia.org/wiki/File:Hypothalamus-Hypophysis-Testicle-Hormone-Axis_%28engl.%29.svg, Creative Commons Attribution-Share Alike 3.0 Unported license Role of kisspeptin in LH surge LH mid cycle surge due to estrogen positive feedback to kisspeptin LH surge triggers ovulation. Phases of the Ovary 2., 3. follicle maturation 4. ovulation 5. corpus luteum formation 6. corpus luteum degeneration image by Shazz (modified), http://commons.wikimedia.org/wiki/File:Order_of_changes_in_ovary.svg , Creative Commons Attribution-Share Alike 3.0 Unported license Key Concepts Differentiation of germ cells as well as synthesis and secretion of sex hormones are the common functions of the ovaries and testes. FSH and LH govern germ cell maturation and sex steroid hormone production in both males and females. As the chosen follicle matures, it produces estrogen which increases its own sensitivity to LH (and FSH) and reduces the amount of FSH released by the pituitary. The reduction in FSH leads to the death of less mature follicles. In females, a second group of kisspeptin neurons is responsible for the ability of estrogen to cause the LH surge. .