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  • 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 sperm 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

Fertilization is the epic story of a single sperm facing incredible odds


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受精 (Fertilization)

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    hkraywai に公開 2021 年 01 月 14 日