For fertilization germ cell is required which is from epiblast during intrauterine life.
A germ cell is bipotential till the 6th week of intrauterine life. The differentiation in male ( Spermatogonia ) and female germ cells (Oogonia).
Spermatogonia have X and Y chromosome. Oogonia have both X chromosome.
Spermatogonia undergoes Spermatogenesis and form sperm.
Oogonia also form Ovum by Oogenesis.
📝 Germ cells divide into 2 types.
1) Mitosis:
In this process cell, divides into 2 daughter cells but the chromosome number remains the same.
2) Meiosis:
Meiosis -1
Cell divide into 2 daughter cell but chromosome number in each cell become half the Parent cell.
Meiosis -2
Cell decided into 2 daughter cell but chromosome number remains same.
SPERMATOGENESIS
Spermatogenesis occurs by Mitosis and Meiosis.
Steps :
Spermatogonia > (Mitosis) > Primary Spermatogonia > (Meosis 1) > Secondary Spermatocyte > (Meosis 2) > Spermatids > (Spermiogenesis) > Spem
From 1 Spermatogonia 64 sperm will be formed.
OOGENESIS :
Oogenesis begins in intrauterine life.
Steps :
Oogonia > (Mitosis) > Primary Oocyst > (enters in Meosis 1 but gets arrested in Diplotene stage of prophase -1 )
Till puberty no further changes
Mitosis takes place after birth.
Now Primary Oocyst is surrounded by follicular cells of the ovary called the primordial follicle.
At puberty, the HPO axis will activate and release GnRH hormone which promotes the release of LH and FSH from the ant pituitary.
LH Hormone starts Meiosis 1 again and forms the Primary polar cell.
Now Primary polar cells take place into Meiosis 2 and get arrested till fertilization.
After fertilization Meiosis 2 starts again and forms a female pronucleus and a secondary polar body.
FERTILIZATION:
Number of events that occurs before fertilization
First of all, we have to see the structure of oocytes.
Pic:
Now...When the male partner ejaculates near the cervix, millions of sperm enter into the cervix.
✓First Capacitation takes place in the female reproductive tract.
Capacitation means the ability of sperm to fertilize ova.
Which begins at the cervix and the majority of Capacitation occurs at the fallopian tube.
It takes 2-6 hours.
After that sperm motility increases and now sperm become hypermotile.
Thousands of sperm try to reach the fallopian tube but only 300-500 sperm will reach There. It takes 30 minutes.
✓Only 1 sperm out of this reach at zona pellucida. 300-500 sperm which attach first at corona radiata will release hyaluronidase enzyme by acrosomal reaction 👉 Which helps 1 sperm to enter in zona pellucida.
Now sperm enters in perivitelline space.
✓ Now after that Primary oocyte goes under 2nd meiotic and form the female pronucleus and 2nd polar body.
✓ Now sperm touches ooplasm and cortical granules of it release an enzyme ( Cortical Reaction ) which prevents other sperm to enters into zona pellucida. ( Zona Reaction )
Now we can tell this zona pellucida prevents polyspermy.
Now head of sperm with nuclear material fuses with female pronucleus and FERTILIZATION will take place.
📝 FACTS ABOUT FERTILIZATION
1) Time is taken to spermatogenesis; 72-74 days
2) average sperm produced/day: 100 million sperms/day
3) site of spermatogenesis: seminiferous tubules
4 ) sperm remain motile in the female genital tract for 12 hours.
5) Time is taken for sperm to reach the ampulla of the fallopian tube - 30 mins.
6) the First stimulus for testis to produce testosterone - HCG
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