Fertilization

Fertilization is the epic story of a single sperm facing incredible odds 0:08 To unite with an egg and form a new human life it is the story of all of us 0:19 During sexual intercourse about 300 million sperm enter the vagina 0:27 Soon afterward millions of them will either flow out of the vagina 0:33 or die in its acidic environment 0:35 However many survive because of the protective elements provided in the fluid surrounding them 0:42 Next the sperm must pass through the cervix and opening into the uterus 0:48 Usually it remains tightly closed but here the cervix is open for a few days while the woman ovulates 0:55 The sperm swim through the Cervical Mucus which is thinned to a more watery consistency for easier passage 1:04 Once inside the cervix the sperm continue swimming toward the uterus though millions will die trying to make it through the mucus 1:13 Some sperm remain behind caught in the folds of the cervix, but they may later continue the journey as a backup to the first group 1:23 Inside the uterus muscular uterine contractions assist the sperm on their journey Toward the egg 1:30 However resident cells from the women's immune system mistaking the sperm for foreign invaders, destroy thousands more 1:44 Next half the sperm head for the empty Fallopian Tube while the other half swim toward the Tube containing the unfertilized egg 1:53 now 1:54 only a few thousand remain 1:57 Inside the Fallopian Tube tiny cilia pushed the egg toward the Uterus 2:02 To continue the sperm must surge against this motion to reach the egg 2:07 Some sperm get trapped in the cilia and die 2:11 during this part of the journey chemicals in the reproductive tract cause the membranes covering the heads of the sperm to change 2:18 as a result, the sperm become hyperactive 2:21 swimming harder and faster toward their destination 2:26 at long last the spam reached the egg 2:32 only a few dozen of the original 300 million sperm remain 2:37 The egg is covered with a layer of cells called the Corona radiata 2:42 The sperm must pushed through this layer to reach the outer layer of the egg the Zona Pellucida 2:49 When sperm reached the Zona Pellucida they attach to specialized sperm receptors on the surface 2:56 Which triggers their acrosomes to release digestive enzymes 3:01 enabling the sperm to burrow into the layer 3:06 Inside the Zona Pellucida is a narrow fluid filled space just outside the egg cell membrane 3:14 The first sperm to make contact will fertilize the egg 3:19 After a perilous journey and against incredible odds a single sperm attaches to the egg cell membrane 3:27 Within a few minutes their outer membranes fuse and the egg pulls the sperm inside 3:34 This event causes changes in the egg Membrane that prevent other sperm from attaching to it 3:41 Next the egg releases chemicals that push other sperm away from the egg