`=>` `color{blue}"Oogenesis"` : The process of development of an `color{Violet}"oocyte from oogonia"` in the female gonads.

`=>` `color{blue}"Oogonia"` : A diploid cell that arises from a `color{Violet}"primordial germ cell"` and differentiates into an oocyte in the ovary of female animals.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● The process of formation of a `color{Violet}"mature female gamete"` is called `color{Violet}"oogenesis"`.

● It is markedly `color{Violet}"different"` from spermatogenesis.

● Oogenesis is initiated during the `color{Violet}"embryonic development"` stage when a couple of `color{Violet}"million"` `color{Violet}"gamete mother cells"` (oogonia) are formed within each fetal ovary.

● `color{Violet}"No more oogonia"` are formed and added after birth.

● These cells start division and enter into `color{Violet}"prophase-I"` of the `color{Violet}"meiotic division"` and get `color{Violet}"temporarily arrested"` at that stage, called `color{Violet}"primary oocytes"`.

● Each primary oocyte then gets surrounded by a layer of `color{Violet}"granulosa cells"` and then called the `color{Violet}"primary follicle"`.

`=>` `color{blue}"Granulosa cells"` : A granulosa cell is a `color{Violet}"somatic cell"` that is closely associated with the developing female gamete (called an `color{Violet}"oocyte or egg"`) in the ovary of mammals and produce `color{Violet}"sex steroids"`.

`=>` `color{blue}"Theca cells"` : Theca cells are the `color{Violet}"endocrine cells"` associated with `color{Violet}"ovarian follicles"` that play an essential role in fertility by producing the `color{Violet}"androgen substrate"` required for ovarian estrogen biosynthesis.

`=>` `color{blue}"Ovarian Follicles"` :They are the roughly `color{Violet}"spheroid cellular aggregation"` set found in the ovaries that `color{Violet}"secretes hormones"` that influence stages of the menstrual cycle.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● Therefore, at puberty only `color{Violet}"60,000-80,000"` primary follicles are left in each ovary.

● The primary follicles get surrounded by more layers of `color{Violet}"granulosa cells"` and a `color{Violet}"new theca"` and called `color{Violet}"secondary follicles"`

● The secondary follicle soon transforms into a `color{Violet}"tertiary follicle"` which is characterised by a fluid filled cavity called `color{Violet}"antrum"`.

● The `color{Violet}"theca layer"` is organised into an inner `color{Violet}"theca interna"` and an outer `color{Violet}"theca externa"`.

● It is at this stage that the `color{Violet}"primary oocyte"` within the tertiary follicle `color{Violet}"grows in size"` and completes its first meiotic division.

●It is an `color{Violet}"unequal division"` resulting in the formation of a large haploid `color{Violet}"secondary oocyte"` and a tiny first `color{Violet}"polar body"`.

● The secondary oocyte retains bulk of the `color{Violet}"nutrient rich cytoplasm"` of the primary oocyte.

● The tertiary follicle further changes into the `color{Violet}"mature follicle"` or `color{Violet}"Graafian follicle"`.

● The secondary oocyte forms a new membrane called `color{Violet}"zona pellucida"` surrounding it.

● The Graafian follicle now ruptures to release the `color{Violet}"secondary oocyte (ovum)"` from the ovary by the process called `color{Violet}"ovulation"`.