1. A Chemical Signal Balancing Act
Reproduction
A Chemical Signal Balancing Act

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

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

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

7. Estrogenical tyranny
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.
Endometrium = lining of uterus

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

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

10. Day 2-5 FSH …. stimulates follicle growth LH aids in follicle growth
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
Slow rise in estrogen levels
Only one follicle matures the others disintegrate
Mature follicle causes
rapid rise in estrogen

12. Ovulation: day 14
Rapid rise in estrogen causes positive feedback on day 13….
a) Hypothal secretes surge of GnRH
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)

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

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

15. Drop in estrogen and progesterone cause menstruation to begin