Theory:

In this theory, let us study the female reproductive system. The female reproductive system is comprised of:
 
1. A pair of ovaries
 
2. A pair of oviducts or fallopian tube
  
3. A uterus, vagina and external genitalia - vulva
 
512px-Female_genital_system_-_Front_view_1.svg.png
Female reproductive system
 
Functions of the  female reproductive system:
  • To produce eggs
  • To receive the sperms
  • To provide the site where fertilization, implantation of the growing embryo and development of the foetus takes place.
  • It produces hormones that control the different stages of ovulation and maintenance of  pregnancy.
Structure of Ovary:
Ovaries are the primary sex organs present in the female. They have paired structures that are located on either side of the lower abdomen. Each of the ovaries is an almond-shaped body, about \(2\) - \(4\) \(cm\) in length. They lie near the lateral end of the fallopian tube.
 
The ovarian ligament attaches the ovary to the uterus. Each ovary is a compact structure covered by a layer of cubical epithelium known as the germinal epithelium. Beneath the epithelium is the tunica albuginea (connective tissue layer).
 
The ovarian stroma lies below the tunica albuginea. The ovarian stroma consists of a dense outer cortex and an inner medulla. The cortex contains numerous ovarian follicles in various developmental stages.
 
In early fetal development, the primitive germ cells or the primordial germ cells in the ovaries differentiate into oogonia. The oogonia divide rapidly and become primary oocytes. Each of the primary oocytes is surrounded by a layer of epithelial cells called granulosa cells to form primary follicles. The follicles undergo maturation in various stages.
 
More layers of granulosa cells surround primary follicles to form secondary follicles. The secondary follicles changes into a tertiary follicle that is characterized by the presence of a fluid-filled cavity called the follicular antrum.  
 
The tertiary follicle grows in size and is converted into a mature follicle or Graafian follicle. The Graafian follicle ruptures to release the ovum.
  
Oogenesis_Labeled.svg
Anatomy of ovaries 
 
We have seen that the primary oocyte is developed into the primary follicles. The primary oocytes are arrested in the prophase of the first meiotic division. No further development takes place until the girl becomes sexually mature. When the primordial follicle is stimulated, it becomes a primary follicle.
 
The number of primordial follicles in a newborn girl child ranges from about \(7 \) \(million\). When a girl enters puberty, approximately only \(25\)\(\%\) of follicles remain. At puberty, the number of follicles is around \(60,000\) to \(70,000\).
 
During a women's lifetime, she ovulates nearly \(300\) to \(400\) of the \(1\)- \(2 \) \(million\) eggs she was born with. On the other hand, men produce over \(500 \) \(billion\) sperms in their lifetime.
 
Below is a video that explains on the oocytes and follicles:
 
Reference:
https://commons.wikimedia.org/wiki/File:Female_genital_system_-_Front_view_1.svg
https://commons.wikimedia.org/wiki/File:Oogenesis_Labeled.svg
https://www.youtube.com/watch?v=49vhPLVpz8k