In this presentation oogenesis , folliculogenesis and ovulation is discussed briefly . You can find useful content for your college and school projects.

1. OOGENESIS,FOLLICULOGENESIS
& OVULATON
PRESENTED BY : TANVIR SINGH

2. INTRODUCTION
Development of ovum (oogenesis)
Maturation of follicle
Folliculogenesis
Ovulation
Fate of ovum and follicle

3. Oogenesis/Ovogenesis
What is Oogenesis - “Oogenesis is the process
of formation of female gametes.”
Oogenesis, ovogenesis, is the differentiation of
the ovum (egg cell) into a cell competent to
further develop when fertilized. It is developed
from the primary oocyte by maturation.
Oogenesis is initiated in the embryonic stage.

4. CONT..
After differentiation these oogonia multiply by
mitosis and enter the prophase of first meiotic
division and they are called primary oocyte.
These cells migrate from yolk sacs across the
dorsal mesentry to the genital ridges.
Early in the first week of embryonic
development the primitive germ cells can be
identified in the yolk sac.

5. CONT..
• At the end of oogenesis, the oocytes meiotic prophase
laptotene zygotene stage pachytene stage.
• At this stage the ova are covered by a primary follicular
epithelium and called as primordial follicles.
• The meiotic prophase is arrested and the nucleus of oocyte
become dormant and until stimulated by the gonadotropins
after puberty.
• The nuclear arrest condition is called as dictyate stage .

6. CONT..
• During the late Dictyate stage as ovulation approaches , there is
formation of gel like membrane called zona pellucida.
• Growth of oocyte occurs and Primary follicle become secondary
follicle and continuous stimulation results in formation of antrum .
• Estrogen reaches threshold levels leading to LH surge , which causes
restart of meiosis and extrusion of first polar body and formation of
secondary oocyte.
• With the division the chromosome number in the oocyte is changed
from 2n to 1n haploid .

7. CONT..
• The secondary oocyte retains all the cytoplasm and half the nuclear
material of the primary oocyte and the other half extruded out as polar
body.
• The first meiotic division is completed before (cow, sow, ewe) and after
ovulation (mare and bitches).
• The second meiotic division occurs immediately after the first one. The
second meiotic arrest is released during fertilization process.
• Meiotic division started again results in formation of zygote and
extrusion of second polar body.

9. DEVELOPMENT
OF OVUM
• Upon appropriate stimulation
from circulating FSH/LH .
• Final maturation of the oocyte
within the mature preovulatory
follicles.

11. MATURITION
OF
FOLLICLE

12. Graafian Follicle Structure

14. Two Cell
Steroidogenesis
• Part of the steroid pathway in
 Granulosa
 Theca interna
• Regulated by
 Hypothalamo-pituitary axis
 Paracrine factors

15. theca granulosa
LH
LH-R
cAMP
ATP
CHOL
PREG
PROG
C
StAR
C
C
C
FSH
FSH-R
cAMP
ATP
PKA
Estradiol-17
P450arom
PKA
Estrone
Testosterone
P450arom
Androstenedione
17HSD
blood
17HSD
nucleus
mitochondrion
Andro
cholesterol pool

16. Inhibins and Activins
•At the ovary, inhibins antagonize the actions of activins
•Many gonadal cells produce  subunits
•In ovary - only granulosa produce  subunits

b
Inhibin A
Inhibin B
Activin A
a
Activin AB
Activin B

17. FOLLICULOGENESIS
Folliculogenesis is the maturation of the ovarian
follicle, a densely packed shell of somatic cells that
contains an immature oocyte.
Folliculogenesis describes the progression of a
number of small primordial follicles into large
preovulatory follicles that occurs in part during the
menstrual cycle.
When any follicle is released it continues to grow
until the ovulation or degeneration.
The process of follicular growth and degeneration
known as follicular dynamics occurs continuously
throughout the estrous .

18. Dynamics of antral follicles consist of
1) Recruitment
2) Selection
3) Dominance
4) Atresia

20. As the selected follicle proceeds towards dominance.
Follice continue to produce increasing amount of estrogen and
inhibins.
There are several selected follicles but only one will develop into
dominant follicle due to inhibin levels and reduced blood supply to
other follicles .
Suppresed FSH concentration along with reduced blood supply results
in atresia.

22. Number of follicles that develop
Number of follicles that
develop per estrous cycle
depends on
hereditary/environmental
factors.
In cattle/horses, Each estrous
only 1 egg is released .
In swine, 10-25 follicles ripen
at each estrous.
In sheep, 1-3 reach to maturity
depends on the breed ,age and
stage of season.

23. OVULATION
•Ovulation is the release of oocyte from mature grafian
follicle.
•Ovulation in mammalian occurs at any point on ovarian
surface and in mares its restricted to ovarian fossa.
•There are 2 types of ovulators –
Spontaneous- (eg. Cow, mare, sheep, goat , dog)
Induced ovulators/reflex ovulators-( eg. Cat , mink ,
ferret)

24. STRUCTURE
OF OVUM
• Secondary oocyte
• Vitellus
• Nucleus- phase of 2nd meiotic division
• Vitelline membrane
• Previtelline space
• 1st polor body
• Zona pellucida
• Corona radiata

25. • Preovulatory follicles undergo three major changes during the
ovulatory process -
a) Cytoplasmic and nuclear maturation of the oocyte
b) Disruption of cumulus cell cohesiveness among the cells of
the granulosa layer
c) Thinning and rupture of the external follicular wall

26. • A surge of LH occurs at the beginning of estrous prior to ovulation .
• There is increased blood flow near ovulation occurs , but the destined
follicle receives the largest volume of blood .
• The vascularity of the follicular surface increases except at its
center.
• The LH surge also cause an increase of PGF2α and PGE2 levels.
• PGE2 stimulates production of plasminogen which causes increase in
follicular wall elasticity.

27. • PGF2α causes rupture of the epithelial cell lysosomes at the
follicular epithelium.
• Their hydrolase’s destroy the underlying albuginea cells and
theca cells.
• After lysosomes rupture, epithelial cells are scale off.
• The wall of the follicular apex becomes thin in a
circumscribed area called stigma.

28. PGF2α causes
contraction of the
smooth muscle cells of
ovarian stroma and
theca externa.
These ovarian
contraction causes
follicular rupture and
causes expulsion of
oocyte.
After follicular rupture
viscous mass spread at
the ovarian surface to
facilitate the pickup of
oocyte by the fimbriae.

29. Species Ovulation Type Duration of Estrous Ovulation time
Cow Spontaneous 14-18 hrs 12-18 hrs after end of
estrous
Mare Spontaneous 4-7 days Last 2 days of estrous
Sows Spontaneous 2-3 days Last day of estrous
Ewe Spontaneous 1-2 days Last day of estrous
Bitch Spontaneous 7-9 days First 3 days of estrous
Cat / Mink / ferret Induced 4 days if copulation occurs
9 -10 days without
compilation
1 day after meeting no
ovulation if copulation does
not take place.