Question

What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle?

Answer 1

Primary oocyte:

Oogonia or the egg mother cell begins the first meiotic division but is arrested at the prophase I. This is the primary oocyte.



Primary follicle:

Primary oocytes get surrounded by a layer of granulosa cells and form the primary follicle. A large number of these follicles degenerate during the phase from birth to puberty






Secondary follicle:

Primary follicles are surrounded by more layers of granulosa cells and change into secondary follicles.




Tertiary follicle:

Secondary follicle develops a fluid filled cavity called antrum and transforms into tertiary follicles. It has theca externa and theca interna. This occurs once the first meiotic division is completed in the primary oocyte.





Graafian follicle:

Tertiary follicle converted into Graffian follicle. Graafian follicles contain the secondary oocyte which is arrested in the metaphase of meiosis II. This is released during ovulation.