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1. 0:04Ovulation is a part of the menstrual cycle when the ovary releases a ripe egg, or ovum.
2. 0:11Inside the ovary are hundreds of thousands of follicles.
3. 0:14Each follicle is a hollow ball of cells with an immature egg in the center.
4. 0:19The typical 28-day menstrual cycle
5. 0:22begins on the first day of menstrual bleeding.
6. 0:26During the first 7 days of the cycle,
7. 0:28a few follicles begin to grow at the same time.
8. 0:31These maturing follicles secrete estrogen hormone into the blood stream
9. 0:36to prepare the lining of the uterus for pregnancy.
10. 0:42Around Day 7, all of the follicles stop growing,
11. 0:45and begin to degenerate, except for one.
12. 0:49This dominant follicle continues to grow
13. 0:52and nourishes the developing egg inside it.
14. 0:56Around Day 12, the follicle secretes a large amount of estrogen into the blood stream.
15. 1:02When the estrogen reaches the hypothalamus and the pituitary gland in the brain,
16. 1:07the anterior, or front part, of the pituitary gland
17. 1:10releases a huge surge of luteinizing hormone
18. 1:13into the blood stream.
19. 1:14Around day 14, luteinizing hormone
20. 1:18causes the follicle to undergo a sudden growth spurt.
21. 1:21Right before ovulation,
22. 1:23the egg detaches from the inside of the follicle.
23. 1:26The bulging follicle releases chemicals,
24. 1:28causing one of the two fallopian tubes
25. 1:31to move in closer and surround the follicle.
26. 1:39The follicle swells until it bursts open,
27. 1:41ejecting the egg and fluid from the follicle
28. 1:44into the abdominal cavity.
29. 1:48In response, the fimbriae, tiny projections
30. 1:51at the end of the fallopian tube,
31. 1:54sweep across the ovulation site and pick up the egg.
32. 1:57Microscopic cilia on the fimbriae's surface
33. 2:01transport the egg to the entrance of the fallopian tube.
34. 2:04Inside the walls of the fallopian tube,
35. 2:06muscular contractions gently push the egg toward the uterus.
36. 2:11After ovulation, the egg lives for 12-24 hours,
37. 2:16so it must be fertilized by a sperm from the male
38. 2:19during this time for a woman to become pregnant.
39. 2:22If it is not fertilized, the egg dissolves away
40. 2:25and is shed along with the uterine lining during menstruation.