Oogenesis and follicular development Part 1 I Endocrine Physiology I The slides will talk about 1. Introduction 2. Stages of follicular development 3. Primordial follicle 4. Preantral follicle (primary and secondary follicle) 5. Antral follicle You can also watch the same topic on HM Learnings Youtube channel. You can also follow HM Learnings on facebook, instagram and twitter for daily updates

2. Oogenesis
• Process of development of female gamete (ovum).
• Begins in the fetal period
• During the 4th week of gestation, primordial germ cells migrate from the
yolk sac to the gonadal ridge and forms oogonia mitotically.
• This will continue up to the 20 weeks, resulting in formation of about 7
million oogonia.
• At this point, oogonia enter meiosis I and form primary oocyte
(arrested at diplotene stage of prophase I)

3. Stages of follicular development
• Ovarian follicle is a functional unit of ovary
• Life history of follicles:
1. Primordial follicle
2.Primary and secondary follicle (preantral follicle)
3.Tertiary follicle (antral follicle)
4.Graafian follicle (preovulatory, dominant)
5.Dominant follicle within the periovulatory period
6.Corpus luteum
7.Atretic follicles

4. Primordial follicle
• Structure- earliest and simplest follicles
• Primary oocytes get surrounded by single layer of flat pregranulosa cells to
form a primordial follicle during midgestation.
• Primordial follicles are the ovarian reserve, determines the reproductive age
in life span of women.
• Many of these undergo follicular atresia and only some enters into the growth
phase
• Since there number is fixed, the rate at which these die or grow will
determine the reproductive life span of women.
• The rate at which primordial follicles enter the growth process is independent
of pituitary gonadotropins. And is depend primarily on intraovarian paracrine
factors produced by both the follicle cells and oocytes.

6. • Gamete – primary oocyte (arrested at diplotene stage of Prophase I of
meiosis I )
• This arrest occurs due to maturational incompetence or lack of the cell
cycle proteins needed to support the completion of meiosis like cyclin
B, CDK1.

7. Preantral follicle- Primary &
Secondary
• Structure- first stage of follicular growth
• Cuboidal granulosa cells surround the primary oocyte and form primary follicle
• As granulosa cells proliferate, they form a multilayered (i.e., stratified) epithelium
around the oocyte. At this stage the follicle is referred to as a secondary follicle
• After secondary follicle acquires 3 to 6 layers of granulosa cells, it secretes paracrine
factors that induce nearby stromal cells to differentiate into epithelioid thecal cells.
• Once a thecal layer forms, the follicle is referred to as a mature preantral follicle
• Mature follicle then moves from outer cortex to inner cortex , near to the medullary
vasculature. It release angiogenic factors and induce the formation of arterioles to
form a vascular wreath around the follicle

9. • Gamete- primary oocyte secretes glycoprotein such as ZP1, ZP2 and
ZP3 to form zona pellucida
• It provides species specific sperm binding sites
• Endocrine function- Granulosa cells express FSH receptor, but these
are responding only to oocyte secreted factors
• No production of ovarian hormone at this stage.
• Theca cells express LH receptor
• Minimal production of androstenedione at this stage

10. Antral follicle
• Structure- Preantral follicles increase in size. Fluid filling spaces appears
between the granulosa cells and coalesce into the antrum
• 100-fold increase in the granulosa cells and swelling of antral cavity
divides the granulosa cells into two discrete populations: mural
granulosa cells (stratum granulosum) and cumulus cells (cumulus
oophorus and corona radiata)
• Early antral follicles are dependent on pituitary FSH for normal growth.

12. • Gamete- During the antral stage the oocyte synthesizes sufficient
amounts of cell cycle components so it becomes competent to complete
meiosis I at ovulation.
• In early primary and secondary follicles, the oocyte is arrested dur to
lack of meiosis associated proteins
• But at antral stage, it reaches the meiotic competence but still is arrested
until the midcycle LH surge

13. Mechanism of meiotic arrest

14. Endocrine function

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