2. Sperm Egg Human Reproduction: Ovulation, Semen Production, and Fertilization

3. Sperm race to fertilize the egg

4. Ovulation: when an egg is released from the ovary 1. Egg release from ovary = ovulation 2. Egg travels through the fallopian tube in an attempt to meet with a sperm

5. Fertilization The best time for sperm to meet the egg is soon after ovulation

6. To Recap: Ovulation Egg Ejaculation Sperm Fertilization Implantation Pregnancy

7. Anatomy of the ovum The egg is surrounded by a thick coat called the zona pellucida. The zona is surrounded by the corona radiata, which is many cell layers formed by follicle cells adhering to the egg before it leaves the follicle in the ovary.

8. The sperm must burrow its way through the zona pellucida. (Only one sperm can do this!) Once inside the sperm’s DNA combines with the egg’s DNA.

9. Once fertilized, the egg is now called a zygote. The zygote begins rapid cell division. At the end of this cell division, the zygote becomes a blastocyst. https://www.youtube.com/watch?v=W4pVICcRtxQ

10. Implantation (when the blastocyst burrows into the endometrium) usually happens about 8 days after ovulation.

11. Implantation into endometrium The syncytiotrophoblast erodes the uterine wall during implantation and the begins the production of the placenta. The syncytiotrophoblast also produces the HCG (human chorionic gonadotropin) hormone. This is the hormone that pregnancy tests test for.  The presence of the syncytiotrophoblast = pregnancy.

12. Placenta The placenta provides oxygen and nutrients to the fetus, while removing carbon dioxide and other waste products.

13. Timeline Day 0 – Day 5: Zygote Day 5 – Day 10: Blastocyst Week 2 – week 7: Embryo Week 8 – week 40: Fetus

14. Day 0 – Day 5: Zygote A zygote immediately begins to divide and grow into a ball of cells called a blastocyst. Day 5 – Day 10: Blastocyst The thin layer becomes the placenta, an organ that regulates fetal development. The thick section of the blastocyst will become the embryo itself. Week 2 – week 7: Embryo Major internal organs and external body structures take on identifiable shapes. The heart forms and begins to pump blood. The brain and spinal cord can be identified. Arms and legs sprout and take shape. Week 8 – week 40: Fetus Structures that have already formed continue to grow and develop.

15. Sex differentiation – how reproductive organs develop in utero Sperm determines the sex of the embryo/fetus But no matter what the sex is, male and female embryos begin with the same fetal reproductive system

16. All embryos begin with this structure The PINK tract is called the Mullerian duct. It will become the female reproductive system. The BLUE tract is called the Wolffian duct. It will become the male reproductive system. The circles are the gonads and will eventually become the ovaries or the testicles.

17. How does this happen? SRY is a gene located on the Y chromosome and is ESSENTIAL for the development of the testes. Once the testes develop, the leydig cells make testosterone Male sex hormones are XY and females are XX

18. The presence of testosterone retains the wolffian duct and develops it into the male reproductive system Meanwhile, sertoli cells produce a hormone called MIS (mullerian inhibiting substance), which disintegrates the mullerian duct

19. What about in the female? Male sex hormones are XY and females are XX Female only has XX chromosome, no Y chromosome  No SRY gene  Testes do not develop  No cells make testosterone  Wolffian duct is NOT maintained without the presence of testosterone  Wolffian duct disintegrate  Mullerian duct remains and develops into the female reproductive system

20. So what does all of this mean? The male reproductive system REQUIRES activation in order to development. It needs the SRY gene and testosterone. The female system DOES NOT require activation. It will simply develop without the presence of testosterone. The female reproductive system is the DEFAULT system. It’s not that we all start as females in utero. We all start as the SAME- neither male nor female.

22. Symptoms of Pregnancy Missed period Tender or swollen breasts Nausea (with or without vomiting) Slight bleeding or “spotting” Increased urination Fatigue Food aversions or craving The only way to REALLY determine pregnancy is to take a test.