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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