spermatogenesis oogenesis ovulation fertilization

1. SPERMATOGENESIS, oogenesis,
ovulation, fertilisation

2. SPERMATOGENESIS
• The spermatogenesis is the process of formation of
spermatozoa from primordial germ cells (PGCs) present
in the walls of the seminiferous tubules of the testis.
▪ At puberty, the PGC undergo a series of divisions to form
spermatogonia.

4. ➢ Thus, four haploid spermatids are produced from the
meiotic division of one primary spermatocyte.
➢ Each spermatid gradually changes its morphology to
become spermatozoa or sperm.
➢ This transformation of circular spermatid into an
elongated spermatozoa is called spermiogenesis.

5. Structure of Spermatozoon
The spermatozoon (50 μ in length) consists of head,
neck, and tail. The tail is further divided into three
: middle piece, principle piece, and end piece.

7. Spermiogenesis
The spermatid is transformed into the spermatozoon as follows:
1. Nuclear material (chromatin) gets condensed and the nucleus moves
towards one pole of the cell to form the head of the spermatozoon.
2. Golgi apparatus forms the acrosomal cap.
3. Centrosome divides into two centrioles. One centriole occupy the neck
region-gives rise to the axial filament.

8. The other centriole moves away from the first centriole and
becomes ring shaped - forms an annulus/ring through which
axial filament passes.
4. The part of the axial filament between the neck and annulus
becomes surrounded by mitochondria
5. Most of the cytoplasm of spermatid is shed off but the cell
membrane remains, which covers the entire spermatozoon.

9. oogenesis
✓ The process of maturation and differentiation of primordial germ cell
to oogonia , primary oocytes , secondary oocytes and to mature ova in
female genital tract.
✓ Ova is formed from cells of germinal epithelium lining the ovary
✓ Involves production of haploid nucleus and prelimanary organisation
of cytoplasm

10.  Location : ovarian cortex
 Peculiarities:
-starts before birth(10th week)
-stops in the middle(birth to puberty)
-restarts at puberty(11-13 years)
-continues up to menopause(45-55 years)
 Process:
-mitosis
-meiosis
-growth of follicles
-differentiation of follicles

11. Oogenesis at different phases of life
❖ Before birth
-Before 3rd month:
PGC ----> oogonia(2n)
-Before 7th month:
oogonia continue to divide mitotically
 oogonia are surrounded by a layer of flat epithelial cells
 some oogonia enlarge to form primary oocytes

12. -7th month to birth: formation of primordial follicles.
Primary oocyte enters prophase 1 of meiosis 1
 meiosis is arrested by oocyte maturation inhibitor
factor
 many of these oogonia and primary oocyte degenerate
before birth

13. ❖Birth to puberty
-Both maturation and degeneration of primary follicles
-At the time of birth all primary oocytes are in prophase
of first meiotic division.
-At birth approx. two lakh primary oocytes in primary
follicles are present in each ovary.
-Instead of entering metaphase the primary oocytes enter
prolonged resting or diplotene stage.

14. ❖ After puberty
-The first meiotic division of a primary oocyte produces two
unequal daughter cells
-Each daughter cell has haploid number of chromosome(23)
-The large cell which receives most of the cytoplasm is called
secondary oocyte and smaller cell is known as the first polar body
-The secondary oocyte immediately enters the second meiotic
cell division

15. ▪ Ovulation takes place while the oocyte is in metaphase
▪ The secondary oocyte remains arrested in metaphase till
fertilisation occurs
▪ The second meiotic division is completed only if fertilisation
occurs
▪ This division results in two unequal daughter cells
▪ The larger cell is called ovum and the smaller daughter cell
is called second polar body

16. ▪ The first polar body may also divide during the second
meiotic division making a total of three polar bodies
▪ If fertilisation does not occur the secondary oocyte fails
to complete the second meiotic division and
degenerate about 24 hours after ovulation

17. Folliculogenesis
➢ Primordial follicle
The oogonia are surrounded by stromal cells. some
cells of stroma become flattened and surround a
primary oocyte

18. Primary follicles
➢ primary oocyte
surrounded by a layer of
cuboidal or low columnar
follicular cells
➢ the growing primary
follicle forms a homogenous
layer of glycoprotein in
between follicular cells and
primary oocyte known as zona
pellucida

19. Secondary / multilaminar follicle
➢ the follicular cells undergo mitotic division
and form a multi-layered stratum granulosum
➢ the primary oocyte increases in size upto 40
microns
➢ the follicular cells are now known as
granulosa cells
➢ the primary oocyte receives its nutrition from
granulosa cells upto puberty

20. Preantral follicle
➢ fluid filled spaces appear between granulosa cells
➢ the fluid is secreted by granulosa cells

21. Tertiary / antral follicle
➢ the fluid filled spaces between granulosa cells
coalesce and form bigger cavity known as follicular
antrum
➢ the fluid that is filling the antrum is called liquor
folliculi secreted by granulosa cells
➢ the size of follicle increase due to proliferation of
granulosa cells

22. Mature / Graafian follicle
➢ largest mature follicle(3-5 mm)
➢ it reaches the periphery of the cortex and starts
projecting on to the surface of the ovary
➢ the follicular antrum is filled with fluid pushing
the primary oocyte with a layer of covering cells to
one side

23.  The layer of cells immediately surrounding the
oocyte and zone of pellucida are called corona
radiata cells
 The projection of granulosa cells covering the
primary oocyte projecting into the follicular
antrum is cumulus oophorous

24.  The stromal cell surrounding the membrana granulosa
become condensed to form a covering called theca
interna (later secrete oestrogen)
 Outside the theca interna some fibrous tissue becomes
condensed to form another covering called theca
externa
 The ovarian follicle is now fully formed and gradually
increase in size and finally burst and expels the
ovum(ovulation)

26. Thank you