FERTILIZATION - The Process and its ways.pptx

Fertilization is the process of sperm and egg fusing to create a zygote, which then develops into a new individual. It is a key part of sexual reproduction.

How does fertilization occur?
Millions of sperm race to reach the egg, but only one breaks through the egg's outer layer.
The fertilized egg, now called a zygote, moves down the fallopian tube.
The zygote divides into two cells, then four, then more cells.
After about a week, the zygote has traveled to the uterus and is now a cluster of about 100 cells called a blastocyst.

Why is fertilization important?
It ensures that each individual has the correct amount of DNA.
It produces genetically unique offspring.
It marks the start of a new life.
Other uses of the word "fertilization":
The process of spreading a natural or chemical substance on land or plants to make them grow well.
The transfer of pollen grains from an anther to a stigma.

1. FERTILIZATION

2. GAMETO GENESIS The process of maturation of germ cells ( ovum and sperm ) is called as gametogenesis. There are two process in gametogenesis. 1. oogenesis . 2. spermatogenesis.

3. FERTILIZATION

4. FERTILIZATION DEFINATION: Fertilization is the process of fusion of the spermatozoon with the mature ovum. The fertilization process takes approximately 24 hours .

5. Oocyte Transport The secondary oocyte is expelled at ovulation from the ovarian follicle with the escaping follicular fluid. During ovulation, the fimbriated end of the uterine tube becomes closely to the ovary. The fimbriae , move back and forth over the ovary.

6. By the sucking action the ovum aspirated by the fimbriae and moves towards the infundibulum of the uterine tube. The oocyte passes into the ampulla of the tube, due to peristalsis -movements of the wall of the uterine tube, the ovum pass towards the uterus.

7. Sperm Transport Nearly 2 to 6 ml of sperm are ejaculated in single act of coitus . From 200 to 60 millions sperms are deposited around the external os of the uterus and in the fornix of the vagina during sexual intercourse. The sperms pass slowly through the cervical canal by movements of their tails.

8. The enzyme vesiculase , produced by the seminal glands, coagulates some of the semen and forms a vaginal plug that may prevent the backflow of semen into the vagina. The sperms move 2 to 3 mm/minute , but the speed varies with the pH of the environment. They move slowly in the acid environment of the vagina, but move more rapidly in the alkaline environment of the uterus .

9. Only approximately 200 sperms reach the fertilization site. Most sperms degenerate and are resorbed by the female genital tract. The viability of human oocytes are usually 12 – 24 hrs. If it is not fertilized with in 24 hours it degenerates shortly thereafter. The viability of Sperms are usually 48 – 72 hrs.

10. PHASES OF FERTILIZATION

11. 1 ST PHASE: Passage of a sperm through the corona radiata. Dispersal of the follicular cells of the corona radiata surrounding the oocyte and zona pellucida enzyme hyaluronidase released from the acrosome of the sperm, t ubal mucosal enzymes and m ovements of the tail of the sperm are important in its penetration of the corona radiata.

12. 2 ND PHASE: Penetration of the zona pellucida Passage of a sperm through the zona pellucida. The enzymes esterases , acrosin , appears to cause lysis of the zona pellucida, thereby forming a path for the sperm to follow to the oocyte.

13. Once the sperm penetrates the zona pellucida , a zona reaction -a change in the properties of the zona pellucida -occurs making it impermeable to other sperms. The zona reaction due to the action of lysosomal enzymes released by cortical granules near the plasma membrane of the oocyte . They cause changes in the plasma membrane that make it impermeable to other sperms.

14. 3 RD PHASE: Fusion the oocyte and sperm. The oocyte and sperm fuse and break down at the area of fu sion. The head of the sperm enter the cytoplasm of the oocyte, but the sperm's plasma membrane remains behind

15. 4 th PHASE: Completion of the second meiotic division of oocyte and formation of female pronucleus. Penetration of the oocyte by a sperm activates the oocyte into completing the second meiotic division and forming a mature oocyte and a second polar body. the mature female pronucleous contains the haploid number of the chromosome ( 23 x ).

16. 5 TH PHASE Formation of the male pronucleus. The nucleus of the sperm enlarges to form the male pronucleus and its containing haploid number of the chromosome ( 23 x or y ).

17. 6 TH PHASE As the pronuclei fuse into a single diploid number of chromosomes, is called as zygote . The chromosomes in the zygote become arranged on a cleavage spindle in preparation for cleavage of the zygote

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