1. Reproduction A Chemical Signal Balancing Act

2. Testis signaled to make sperm Low Testosterone in blood detected by Hypothalamus Low Testosterone in blood detected by Hypothalamus Hypothal. Secretes GnRH Hypothal. Secretes GnRH (gonadotropin-releasing hormone) (gonadotropin-releasing hormone) GnRH travels through capillaries to Ant pit. GnRH travels through capillaries to Ant pit. GnRH causes the Anterior pituitary to release gondadotropins. GnRH causes the Anterior pituitary to release gondadotropins. Gonadotropins are hormones that work on gonads (in this case testes) Gonadotropins are hormones that work on gonads (in this case testes) LH and FSH LH and FSH

3. Sperm Production: actionof gonadotropins in testis LH causes Leydig cells to make testosterone LH causes Leydig cells to make testosterone Testosterone aids in sperm production Testosterone aids in sperm production FSH trigger Sertoli cells to signal primary spermatocytes to differentiate into sperm FSH trigger Sertoli cells to signal primary spermatocytes to differentiate into sperm

4. Negative Feedback Loops 1) High sperm count causes sertoli cells to 1) High sperm count causes sertoli cells to Relaese inhibin Relaese inhibin Inhibin travels in blood to Hypothal and ant. Pit Inhibin travels in blood to Hypothal and ant. Pit Inhibits production of GnRH and LH Inhibits production of GnRH and LH 2) High testosterone levels provide negative feedback to Hypothal. 2) High testosterone levels provide negative feedback to Hypothal. GnRH production is inhibited GnRH production is inhibited

7. Estrogenical tyranny FYI….pms happens when estrogen levels are too low…. FYI….pms happens when estrogen levels are too low…. Low estrogen and progesterone levels cause menstruation.. upper 2/3 of endometrium disintegrates due to constriction of uterine arterioles. Low estrogen and progesterone levels cause menstruation.. upper 2/3 of endometrium disintegrates due to constriction of uterine arterioles. Endometrium = lining of uterus Endometrium = lining of uterus

8. Endometrial glands secrete nutrient fluid to sustain the embryo before implantation

9. Day 1…… Menstruation begins & Menstruation begins & Low levels of estrogen & progesterons let hypothal secrete GnRH (high levels inhibit GNRH) Low levels of estrogen & progesterons let hypothal secrete GnRH (high levels inhibit GNRH) GnRh travels in capillaries to Ant pit. GnRh travels in capillaries to Ant pit. Ant pit makes small amount of the Gonadotropins LH and FSH Ant pit makes small amount of the Gonadotropins LH and FSH

10. Day 2-5 FSH …. FSH …. stimulates follicle growth stimulates follicle growth LH aids in follicle growth LH aids in follicle growth Growing follicle begins to release estrogen Growing follicle begins to release estrogen

11. Follicular phase Day 1-13 Several follicles begin to grow, an oocyte begins to mature in each follicle Several follicles begin to grow, an oocyte begins to mature in each follicle Slow rise in estrogen levels Slow rise in estrogen levels Only one follicle matures the others disintegrate Only one follicle matures the others disintegrate Mature follicle causes Mature follicle causes rapid rise in estrogen

12. Ovulation: day 14 Rapid rise in estrogen causes positive feedback Rapid rise in estrogen causes positive feedback on day 13…. a) Hypothal secretes surge of GnRH a) Hypothal secretes surge of GnRH b) GnRH causes ant pit to release LH surge b) GnRH causes ant pit to release LH surge On day 14 High levels of LH cause ovulation: follicle and ovary wall rupture and secondary oocyte release (ovulation) High levels of LH cause ovulation: follicle and ovary wall rupture and secondary oocyte release (ovulation)

13. Oogenesis Follicle is mature when meiosis I is completed Follicle is mature when meiosis I is completed Secondary oocyte is arrested at Metaphase II until fertilization Secondary oocyte is arrested at Metaphase II until fertilization

14. Luteal phase Day 15-28 LH causes Empty follicle become the …… LH causes Empty follicle become the …… corpus luteum corpus luteum Corpus luteum secretes progesterone and estrogen Corpus luteum secretes progesterone and estrogen High progesterone and estrogen exert negative feedback on hypothal and ant pit High progesterone and estrogen exert negative feedback on hypothal and ant pit Prevent GnRH and FSH and LH production Prevent GnRH and FSH and LH production Maintain endometrium until Corpus luteum disintegrates at about day 25 Maintain endometrium until Corpus luteum disintegrates at about day 25

15. When corpus luteum disintegrates…. When corpus luteum disintegrates…. Drop in estrogen and progesterone cause menstruation to begin Drop in estrogen and progesterone cause menstruation to begin Unless…….. Unless…….. Fertilization has occurred. Fertilization has occurred. Blastocyst secretes HCG (human chorionic godadotropin) that keeps the corpus luteum intact Blastocyst secretes HCG (human chorionic godadotropin) that keeps the corpus luteum intact Pregnancy tests detect HCG in urine Pregnancy tests detect HCG in urine

16. Fertilization Sperm travel up oviduct to meet secondary oocyte Sperm travel up oviduct to meet secondary oocyte Meiosis II takes place after fertilization Meiosis II takes place after fertilization Egg nucleus and sperm nucleus fuse Egg nucleus and sperm nucleus fuse Mitosis begins (cleavage) Mitosis begins (cleavage) 3-4 days after fertilization 3-4 days after fertilization

17. By 4 days 16-32 cell morula By 4 days 16-32 cell morula By day 5 blastocyst By day 5 blastocyst Days 6-7 implantation Days 6-7 implantation