2. PRIMORDIAL GERM CELL
• Gametes are derived from PGCs.
• Formed in the epiblast during the 2nd wk of
intrauterine life and move to the wall of yolk sac.
• During 4th wk migrate from the yolk sac toward
the developing gonads, arrive at the end of 5th
wk.
• Mitotic division increase their number during
migration.
3. In preparation for fertilization, germ
cells undergo gameto-genesis, which
includes meiosis, to reduce the
number of chromosomes and cyto-
differentiation to complete their
maturation.
PRIMORDIAL GERM CELL cont.
4. GAMETOGENESIS
a. Oogenesis
stages of meiosis in the female
ovarian maturation, hormones and cycles
ovulation
b. Spermatogenesis
stages of meiosis in the male
differentiation (spermiogenesis)
OUTLINE
5. SOME TERMS
Gamete: egg or sperm
Gametogenesis: production of eggs or sperm
Oogenesis: production of eggs
Spermatogenesis: production of sperm
Spermiogenesis: differentiation of sperm morphology
Follicle: where eggs mature in the ovary
Ovulation: release of egg from follicle
Polar body: nonfunctional product of meiotic
divisions in oogenesis
Zygote: Fertilized egg
9. Gonad
Yolk sac
PGCs
PGCs
Differentiate
Mitotic div.
End of 3rd month
arranged in clusters,
surrounded by simple
flates epithelial cells
Derived from surface epithelium covering the ovary
Continue to divide till 5th
month, maximum
7million,then cell death begin
Primary oocyte
arrest in prophase I
oogonia
Many oogonea &
primary oocyte -
atretic
7th month
Primary oocyte
arrest in prophase I
Primordial follicle
Maturation of oocytes begins before birth
10. Maturation of oocytes continues at puberty
X
Metaphase
Primary oocytes remain arrested in prophase and do not finish
their first meiotic division before puberty is reached
Primary oocyte Prophase of meosis I
Diplotene stage
(resting stage)
Why ?
11. • A small peptide secreted by follicular cells
• Primary oocytes remain arrested in prophase
and do not finish their first meiotic division
before puberty is reached
• Total number of primary oocyte at birth- 6 lac
to8 lac.
• During childhood- most of atretic
• At puberty- 4 lac (out of them 500 will be
ovulated)
Oocyte maturation inhibition factor
12. At puberty….
• Each month- 15 to 20 follicle selected
from the pool of growing follicle and
begins to mature.
• Process is divided into three stages:
1) Primary- preantral
2) Secondary- antral – longest
3) Preovulaatory (grafian follicle)- 37 hours
14. • Theca folliculii: Granulosa cells rest on
a basement membrane, separating
them from surrounding stoma cells by
theca folliculii.
• As the follicle grow it differentiate into
theca interna and externa.
• Zona-pellucida: Granulosa cells and
oocyte secrete a layer of glycoprotein
on the surface of the oocyte.
Pre-antral stage cont…..
15. Stage II- Antral stage
• Fluid filled spaces appear between
granulosa cells
• Coalescence of these spaces from the
antrum
• Follicle with the antrum – secondary
follicle
• Cumulus oophorus: granulosa cell
surrounding the oocyte remain intact
• Number of follicles begin to develop, but
usually only one reaches full maturity,
rest become atretic.
16. Stage III- Pre-ovulatory stage
• Meosis I is completed
• Formation of tow daughter cells of unequal
size each with 23 pair of chromosomes.
• The daughter cells: secondary oocyte and
1st polar body.
• 1st polar body lies between zona-pallucida
and cell membrane of secondary oocyte in
peri-vitelline space.
17. Pre-ovulatory stage cont….
Meosis II
But arrest in
metaphase
3 hour before
ovulation
Secondary
oocyte
- Meiosis II is completed only if the oocyte is fertilize;
other wise, the cell degenerate approximately 24 hours
after ovulation.
- The first polar body also undergoes a second division.
18. SOME MORE TERMS
Oogonia: mitotically dividing cells in the ovary, will become
Oocytes
Primary oocyte: decision has been made to undergo
meiosis, cell has grown. Cells are arrested at this stage
until puberty.
Secondary oocyte: has completed first meiotic division
the division was unequal in terms of cytoplasm
Ovum: Ovulated egg, ready to be fertilized. If fertilized,
the second meitoic division will occur, another polar body
will be given off.
22. SPERMATOGENESIS
• Begins at puberty, includes all of the events by
which spermatogonia are transformed into
spermatozoa.
• Occur at male sex gland: testes, in the
seminiferous tubules.
• Sertoli /sustentacular cells: supporting cells,
derived from the surface epithelium of the
gland.
• Regulated by LH and FSH.
• Time duration of spermatogenesis-74 days.
• Approximately 300 million sperm cells are
produced daily.
23.
24. Spermiogenesis
• The series of changes of resulting in the
transformation of spermatid into
spermatozoa.
• These changes include:
a) Formation of acrosome
b) Condensation of the nucleus
c) Formation of neck, middle piece, and
tail
d) Shedding of most the cytoplasm
28. End results of gametogenesis
• The divisions that create gametes result in 4
spermatids in the male and 1 egg in the
female.
• There can be as many as 3 polar bodies that
also form in the female. They are small and
have sacrificed their cytoplasm and organelles
for the good of the one large egg.
