Oogenesis is the process of forming female gametes called ova, beginning before birth and involving stages of multiplication, growth, and maturation. It is hormonally controlled by the hypothalamic-pituitary system, with FSH and LH stimulating follicle maturation and ovulation, culminating in the release of a secondary oocyte. The significance of oogenesis lies in its essential role in fertilization and reproduction.

1. OOGENESIS
GUIDED BY PRESENTED BY
BIHUNG BASUMATARY PARAG PATGIRI
ASST. PROFESSOR MSC 2ND SEMESTER
DEPT. OF ZOOLOGY ROLL NO- 01
BODOLAND UNIVERSITY DEPT. OF ZOOLOGY
KOKRAJHAR-783370 BODOLAND UNIVERSITY
KOKRAJHAR-783370

2. CONTENT
o INTRODUCTION
o PROCESS OF OOGENESIS
o OVULATION
o HORMONAL CONTROL IN OOGENESIS
o SIGNIFICANCE OF OOGENESIS
o REFERENCES

3. INTRODUCTION
 Oogenesis is the process of formation of female gametes.
 It is the type of gametogenesis through which female gametes are formed.
 Also known as OVA.
 This process begins inside the fetus
before birth.
 The steps in oogenesis up to the
production of primary oocytes occur
before birth.
 The significance of the egg varies
based on the type of organisms.

4.  Primary oocytes do not divide further.
 They either become secondary oocytes or degenerate.
 Oogenesis occurs in the outermost layers of the ovaries.
 Oogenesis starts with a germ cell called oogonium and undergoes mitosis to increase in number.

5. Process of Oogenesis
The process of oogenesis is completed in the following three stages:
1. Multiplication Phase
2. Growth Phage
3. Maturation Phase

6. Multiplication Phase
 Certain cells in the germ epithelium of the ovary of the fetus are larger than others in fetal growth.
 These cells are separated by mitosis.
 Creating a few million egg mother cells or oogonia in each ovary of the fetus.
 The oogonia multiplied by mitotic divisions and form the primary oocytes which pass through the
growth phase.

7. Growth Phase
 The growth phase of the oogenesis is comparatively longer than the growth phase of the
spermatogenesis.
 The size of the primary oocyte increases enormously.
 In the primary oocyte, large amount of fats and proteins becomes accumulated in the form of yolk and
due to its heavy weight.
 It is usually concentrated towards the lower portion of the egg forming the vegetative pole.
 The portion of the cytoplasm containing the egg pro-nucleus remains often separated from the yolk
and occurs towards the upper side of the egg forming the animal pole.
 The cytoplasm of the oocyte becomes rich in RNA, DNA, ATP and enzymes.
 The mitochondria, Golgi apparatus, ribosomes concentrated in the cytoplasm of the oocyte.

8. Maturation Phase
 The maturation phase is accompanied by the maturation or meiotic division.
 First Maturation Division:
 The homologous chromosomes of the primary oocyte nucleus pass through the pairing or synapsis,
duplication, chiasma formation and crossing over.
 The nuclear membrane breaks and the bivalent chromosomes move towards the opposite poles due to
contraction of chromonemal fibers.
 A new nuclear envelope is developed around the daughter chromosomes.
 The unequal cytokinesis occurs and a small haploid polar body or polocyte and a large haploid secondary
oocyte are formed.

9.  Second Meiotic Division:
 The haploid secondary oocyte and first polocyte pass through the second meiotic division.
 The secondary oocyte forms amature egg and a second polocyte.
 By the second meiotic division, the first polocyte also divides into two secondary polocytes.
 These polocytes ooze out from the egg and degenerate while the haploid egg cell becomes ready for the
fertilization.

10. Ovulation
 Development of oocyte takes place in ovaries.
 Every oocyte is neighbored by follicle cells to form a follicle.
 As the menstrual cycle starts, primary oocytes initiate to grow bigger, and follicle cells rise in
number, causing the follicle to grow larger too.
 When a follicle attains maturity, the primary oocyte finishes its primary meiotic division and becomes
secondary oocyte.
 The follicle breaks and secondary oocyte is liberated in the fallopian tube even when the second
meiotic division has not happened.
 Meiosis-II is completed on fertilization.
 This gives off a third polar body.
 If the fertilization does not occur, the oocyte degenerates 24 hours after ovulation while remaining
arrested in meiosis-II cell division.

11. Hormonal Control in Oogenesis

12.  Cyclic changes in the hormonal cycle, governed by the hypothalamic-pituitary system.
 It is responsible for the periodicity of the ovulation.
 The Pituitary releases two hypophysial gonadotropins FSH and LH.
 The pulsating liberation of GnRH by the hypothalamus is the fundamental precondition for a normal
control of the cyclic ovarian function.
 FSH and LH stimulates the maturation of the follicles in the ovary and trigger ovulation.
 Estrogen is produced by the theca interna and follicular cells, progesterone by the corpus luteum.
 The ovarian cycle lasts 28 days.

13. The ovarian cycle is subdivided into two phases:
 Follicle phase:
 Recruitment of a follicle cohort.
 Selection of the mature follicle.
 This phase ends with ovulation.
 Estradiol is the steering hormone.
 Normally, it lasts 14 days, but this can vary considerably.
 Luteal phase:
 Progesterone produced by the corpus luteum.
 It lasts 14 days (relatively constant).

14. Significance of Oogenesis
Oogenesis is the process of formation of female gametes and
WITHOUT OOGENESIS THERE IS NO FERTILIZATION, REPRODUCTION, LIFE !!

15. References
1. Scott F. Gilbert, 2009, “Developmental Biology”, 8Th Edition, Sinauer Associates, Inc. Publishers,
USA.
2. Berry Mitchell, Tam Sharma, 2005, “Embryology an Illustrated color text”, 2nd Edition, Churchill
Livingstone Publishers, Pg: 1-10.
3. https://byjus.com/biology/oogenesis/
4. https://www.embryology.ch/anglais/cgametogen/oogenese04.html

16. THANK YOU