Ovulation

1. Ovulation Each month, a mature egg is released from one of a woman's two ovaries -- this is called ovulation. Ovulation takes place about two weeks after the first day of the last menstrual period.

2. Passage Into the Fallopian Tube Once the egg is released from the ovary, it travels into the fallopian tube where it remains until a single sperm penetrates it during fertilization

3. The Laborious Journey of the Sperm An average ejaculate discharges 40-150 million sperm which eagerly swim upstream toward the fallopian tubes on their mission to fertilize an egg. Fast-swimming sperm can reach the egg in a half an hour, while others may take days. The sperm can live up to 48-72 hours. Only a few hundred will even come close to the egg, due to the many natural barriers and hurdles that exist in the female reproductive tract.

4. Fertilization: Sperm Penetrates Egg If a sperm cell meets and penetrates an egg, it will fertilize the egg. The fertilization process takes about 24 hours. When fertilization happens, changes occur on the surface of the egg to prevent other sperm from penetrating it. At the moment of fertilization, the genetic makeup is complete, including the sex of the infant.

5. The Cells Begin to Divide The fertilized egg begins dividing rapidly, growing into many cells. It leaves the fallopian tube and enters the uterus three to four days after fertilization. Rarely, the fertilized egg does not leave the fallopian tube; this is called a tubal pregnancy or ectopic pregnancy and is a danger to the mother.

6. Implantation After entering the uterus, the fertilized egg attaches to the uterine lining, or endometrium. This process is called implantation. The cells continue to divide

7. At the moment when a lone sperm penetrates a mature egg, conception or fertilization takes place.

8. At ovulation, the mucus in the cervix becomes more fluid and more elastic, allowing sperm to enter the uterus rapidly. Within 5 minutes, sperm may move from the vagina, through the cervix into the uterus, and to the funnel-shaped end of a fallopian tube—the usual site of fertilization. The cells lining the fallopian tube facilitate fertilization.

10. VOCABULARY 1.Zona pellucida-___________________________________________ 2. Cortical granules- ____________________________________________ 3. Zygote - ______________________________________ 4. Cleavage- ____________________________________

11. Day 1: first cleavage- 1 cell becomes 2 Day 2: second cleavage – 4-cell stage Day 3: 6-12 cell stage ( can test for genetic diseases if done by IVF) Day 4: 16-32 cell stage – solid ball of cells – now called a morula

12. Day 5: Solid morula develops into hollow, fluid-filled blastula The embryo will develop from the inner cell mass, or embryonic disc Trophoblasts are the outer layer of the blastocyst that provide nutrients to embryo & develop into a large part of the placenta. First cells to differentiate fro fertilized egg.

13. Day 6-7: Blastocyst attaches to the endometrium and burrows in (implantation) • blastocyst starts to secrete HCG- which keeps estrogen and progesterone levels elevated- prevents another egg to mature • This rise in estrogen and progesterone causes “morning sickness” in some women • Remember – OTC pregnancy tests measure the amount of HCG

15. Days 7-10: Gastrulation; major cellular organization into 2 or 3 (germ) layers • Ectoderm layer: becomes skin, nervous system • Endoderm layer: lining of the gut and internal organs • Mesoderm: muscles, bones , heart • Gastrula: Early embryo with 3 tissue layers. All cells have the same DNA; however, different cells now begin to "turn on" (or "express") different genes to become different organs.

16. Days 10-14: pregnancy becomes established • Amniotic cavity starts to form • Yolk sac starts to form ( this will make germ cells, blood cells • Embryo starts to form from embryonic disc • Chorion (placenta) starts to form • Woman will have just missed her period

17. Day 15-21: Emergence of the vertebrate body plan • Primitive streak starts to form • Site of gastrulation (formation of the three tissue layers • Ectoderm, endoderm, mesoderm • Neural grove begins to form – future spinal cord and brain • Somites begin to form (bands of tissue that become muscles and bones • Pharyngeal arches begin to form – face, neck, mouth, nose

18. Day 21 on – Weeks 3-8: development of all organs Day 22 cardiac cells begin to beat!! Day 24 embryo

19. The first 3 weeks of life are the roughest!! • 1/3 of fertilized zygotes do not make it this far • Causes of miscarriages: • Inheritance of defective set of chromosomes • Errors in mitosis after fertilization • Implantation errors • Ectopic pregnancy

20. Week 4 – bring on the organs!!! Week 4-8 is when most organs are formed and when teratogens are most harmful

21. Week 7/Day 48: first brain waves can be detected Week 8 embryo

22. Week 9- week 40 ( now called a fetus) After 12 weeks or so, the baby's development is largely "finished" - except brain and lung development The fetus just spends much of the 2nd and 3rd trimesters just growing (and doing various flip-turns and kicks inside the amniotic fluid!)

23. Week 16 fetus

27. 5 week old embryo

28. 6 week embryo

29. 20 week old At 9 weeks, fingers are seen

31. http://www.youtube.com/watch?v=RS1ti23SUSw