The internal female reproductive organs consist of the ovaries, uterine or fallopian tubes, uterus, and vagina.
The ovaries are almond-shaped structures that produce steroid hormones like estrogen and progesterone, as well as the female gametes or oocytes.
Each ovary is typically about 3 centimeters long, 1.5 centimeters wide, and 1 centimeter thick, with a thin outer capsule.
The capsule is made up of a thin layer of simple cuboidal epithelium that’s only one cell thick, and an underlying dense layer of connective tissue called the tunica albuginea.
The majority of the ovary consists of the cortex, which is the outer region where oocytes and ovarian follicles develop.
Ovarian follicles are the fluid-filled structures that each contain an oocyte.
This cortex of the ovary has highly cellular connective tissue in comparison to the inner region of ovaries called the medulla, which consists mostly of loose fibroelastic connective tissue with many large, tortuous blood vessels, lymphatic vessels, and nerve fibers.
Alright, let’s take a closer look at the cortex.
The primordial follicles are the follicles found in the outer cortex that develop during fetal life.
At this stage, they actually stop developing, which is called arrested development, and they stay this way until they’re needed for ovulation.
The primary oocyte is the large round cell that makes up the majority of each primordial follicle.
The primary oocytes have a prominent nucleus and a diameter that’s about 25 to 30 um.
The outermost layer of the primordial follicles is a single layer of flattened follicular cells, which are pregranulosa cells.
The zona pellucida is a very thin, pink or eosinophilic layer of glycoproteins that sits between the primary oocyte and the outer follicular cells.
When a primordial follicle continues developing, the next stage of follicular development is called the primary follicle.