Fertilization

Fertilization is the epic story of a single sperm facing incredible odds To unite with an egg and form a new human life it is the story of all of us During sexual intercourse about 300 million sperm enter the vagina Soon afterward millions of them will either flow out of the vagina or die in its acidic environment However many survive because of the protective elements provided in the fluid surrounding them Next the sperm must pass through the cervix and opening into the uterus Usually it remains tightly closed but here the cervix is open for a few

days while the woman ovulates The sperm swim through the Cervical Mucus which is thinned to a more watery consistency for easier passage Once inside the cervix the sperm continue swimming toward the uterus though millions will die trying to make it through the mucus 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 Inside the uterus muscular uterine contractions assist the sperm on their journey Toward the egg However resident cells from the women's immune system mistaking the sperm for foreign invaders, destroy

thousands more Next half the sperm head for the empty Fallopian Tube while the other half swim toward the Tube containing the unfertilized egg now only a few thousand remain Inside the Fallopian Tube tiny cilia pushed the egg toward the Uterus To continue the sperm must surge against this motion to reach the egg Some sperm get trapped in the cilia and die during this part of the journey chemicals in the reproductive tract cause the membranes covering the heads of the sperm to change as a result, the sperm become hyperactive swimming harder and faster toward their destination

at long last the spam reached the egg only a few dozen of the original 300 million sperm remain The egg is covered with a layer of cells called the Corona radiata The sperm must pushed through this layer to reach the outer layer of the egg the Zona Pellucida When sperm reached the Zona Pellucida they attach to specialized sperm receptors on the surface Which triggers their acrosomes to release digestive enzymes enabling the sperm to burrow into the layer Inside the Zona Pellucida is a narrow fluid filled space just outside the egg cell membrane The first sperm

to make contact will fertilize the egg After a perilous journey and against incredible odds a single sperm attaches to the egg cell membrane Within a few minutes their outer membranes fuse and the egg pulls the sperm inside This event causes changes in the egg Membrane that prevent other sperm from attaching to it Next the egg releases chemicals that push other sperm away from the egg and create an impenetrable fertilization membrane As the reaction spreads outward the Zona Pellucida hardens trapping any sperm unlucky enough to be caught inside Outside the egg, sperm are no longer able

to attach to the Zona, Pellucida Meanwhile inside the egg the tightly packed male genetic material spreads out a new Membrane forms around the genetic material creating the male pronucleus Inside the genetic material reforms into 23 chromosomes the female genetic material awakened by the fusion of the sperm with the egg finishes dividing resulting in the female pronucleus which also contains 23 chromosomes as the male and female pronuclei form spider web-like threads called Microtubules pull them toward each other the two sets of Chromosomes joined together Completing the process of fertilization at this moment a unique genetic code

arises instantly determining gender, hair color, eye color and hundreds of other characteristics this new single cell the zygote is the beginning of a new human being and now the cilia and the Fallopian Tube gently sweep the Zygote toward the uterus Where he or she will implant in the richer uterine lining Growing and maturing for the next nine months until ready for birth