a-short-review-of-histology

Secondary Ovarian Follicles:

Follicles which have two or more layers of cuboidal/columnar follicular cells are secondary follicles
The oocyte in a secondary follicle will be larger than is found in a primary follicle
Secondary follicles which have developed to the stage of having only 2 or 3 layers of follicular cells are known as early secondary follicles
Follicles which mature to this stage of development do so in the absence of stimulation from pituitary hormones
This stage of development may be reached by follicles in a prepubertal child although they can develop no further and will become atretic
Development beyond the early secondary stage is dependent on stimulation by the pituitary hormone follicle stimulating hormone (FSH)
This hormone is secreted only during the reproductive stage of a women's life, and in a cyclical manner
In each cycle it will stimulate about 12-15 early secondary follicles in each ovary to develop further
In late secondary follicles, the oocyte continues to increase in size and more layers of follicular cells are laid down
A gelatinous band, the zona pellucida is laid down between the oocyte and the innermost layer of follicular cells
Patches of fluid (follicular fluid) appear between follicular cells
The amount of this fluid increases and eventually pools into one mass of fluid known as the antrum
At this stage of development the follicle becomes known as a Graafian follicle

Micrograph of Secondary Ovarian Follicles:

On the right side of the micrograph a late secondary follicle (part) is shown
Some small pools of follicular fluid (4) are present between follicular cells
At the bottom of the micrograph, two primordial follicles can be seen (arrows)
Note the difference in size between primordial and secondary follicles (and of the primary oocytes contained within each type of follicle)

Micrograph of Ovarian Follicles: