This PPT wil give a overview to Process of gametogenesis and fertilization...

1. Mrs. Smeeta D Mahindrakar
Lecturer
KLEU Institute of Nursing Sciences
Belgaum
Karnataka

2. Gametogenisis

3. Introduction
• Gametogenesis is the general process of gamete
formation in both males and females.
• Oogenesis is the process of meiosis in female
organisms from an oogonium to a primary
oocyte, to a secondary oocyte, and then to an
ovum.

4. • Spermatogenesis is a similar process of forming
sperm by meiosis in males.

5. Process of Oogenesis
• Oogenesis begins soon after fertilization, as
primordial germ cells travel from the yolk
sac to the gonads, where they begin to
proliferate mitotically.
• The germ cells multiply from only a few
thousand to almost 7 million.

6. • They become oocytes once they enter the
stages of meiosis several months after birth.
• Now called primordial follicles, they are
made up of oogenic cells from the
primordial germ cells surrounded by follicle
cells from the somatic line.
• The oocyte is then arrested in the first
meiotic prophase until puberty.

7. • At puberty, between 4 to 10 follicles begin to
develop, although only 1-2 are actually
released. Surrounding each oocyte is a zona
pellucida, membrana granulosa, and theca cell
layer.
• Each oocyte finishes its first meiotic division,
creating a secondary oocyte and polar body,
which serves no further function.
• It begins the next meiosis cycle and is arrested
in its second metaphase, at which point it is
released from the ovary in ovulation.

8. • It will not finish the meiosis cycle until it
encounters the stimuli of a sperm.

10. Spermatogenesis
• Spermtozoa are formed in the wall of
semineferous tubules of the testes.
The various cell-stage in spermatogenesis are
as follows:
• The spermatogonia (type A) or germ cells
(44 +X+Y) divide mitotically, to give rise
to more spermatogonia of type A, and also
to spermatogonia of type A, and also to
spermatogonia of type B.

11. • The spermatogonia (typeB) (44+X+Y)
enlarge, or undergo mitotis, to form primary
spermatocytes.
• The primary spermatocytes (44+X+Y) now
divide so that each of them forms two
secondary spermatocytes. This is the first
meiotic division : it reduces the number of
chromosomes to half.
• Each secondary spermatocyte has 22+X or
22+Y chromosomes. It divides to form
spermatids.

12. • This is the second meiotic division and this
time there is no reduction in chromosome
number.
• Each spermatid 22+X or 22+Y gradually
changes its shape to become a
spermatozoon . This process of
transformation of a circular spermatid to a
spermatozoon is called spermiogenesis.

14. Fertilization
Definition:
• Fertilization means the fusion of two mature
cells an ovum and a spermatozoan to form a
single cell the zygote.
• Fertilization is the process of fusion of
spermatozoan with the mature ovum.

15. Stages
1. Approximation of the gametes.
2. Contact and fusion of the gametes.
3. Effects of fertilization.

16. 1. Approximation of gametes.
It involves the transport of the sperms and
ova in the female genital tract to reach the
uterine tube.
The ovum is picked up after ovulation by
tubal fimbrae and is by muscular or kind of
suction or ciliary action or chemotaxis by tubal
secretions. Then transported to ampullary part.

17. 2. Contact and fusion of the gametes
• A direct contact between the spermatozoa and
the zona pellucida of the secondary oocyte is
necessary before actual fusion of the gametes.
• The cells of corona radiata provide obstacle to
the penetration of the sperms.
• 200 to 300 million sperms emitted at single
ejaculation about 300 to 500 sperms reach the
ovum, only 1 unites with oocyte & rest
engaged in disintegration of corona radiata by
secreting enzyme hyalerinidase

18. • Prior to penetration spermatozoa undergo process
of ;
Capacitation.
Acrosome reaction.

19. Acrosomal reaction

20. 3.Effects of fertilization
 Completion of second
meiotic division of female
gamete:
-It contains haploid number
of chromosomes (22+ X).
The bigger one is female
pronucleus & smaller
polar body pushed to
perivitteline space.
-Head and tail of sperm
enter the cytoplasm. Head
and neck of spermtaozoan
nos of chromosome ie
22+X or 22+Y.

21. •Restoration of diploid nos of chromosomes
in the zygote
• Both male & female
pronuclie meet near
centre of ovum,
nuclear membrane
disappear. This results
in nuclear fusion with
restoration of diploid
nos of chromosome
44+2X or 44+xy

22. • Determination of the chromosomal sex
Out of the total population in that half of them
contain x bearing chromosome and remaining
half contain y bearing .
If x bearing spermatozoon fertilizes an ovum
the zygote contain 2x chromosome +44autosome
& female child is formed & Zygote containing 2y
chromosome +44autosome male child is formed.

23. Initiation of cleavage division of
zygote
• Two cell formed
undergo a series of
division. One cell
divides to form three
cell stage of embryo
followed by 4cell,
8cell, 16cell. This
process of division of
ovum into smaller
cells called
CLEAVAGE

25. • Cleavage reaches 16 cell
stage a cluster/ mass of
cell like mulberry called
‘MORULA’ surrounded
by zonapelucida. Consists
of inner cell mass i.e.
completely surrounded by
outer layer of cell which
gives rise to structure
called ‘TROPHOBLAST’.
Inner cell mass cell gives
rise to embryo called
‘EMBROYOBLAST’.

26. • Some fluid passes into the morula from uterine
cavity and partially separate the cells of inner
cell mass from those of trophoblast & fluid
increases morula acquires shape of cyst.
Trophoblast becomes flattened & inner cell mass
gets attached to inner of trophoblast on one side
and morula becomes BLASTOCYST.

27. Summary