Ovarian follicle
Ovarian follicles or
Graafian follicles (after
Regnier de Graaf) are the roughly spherical
cell aggregations in the
ovary containing an
ovum and from which the egg is released during
ovulation.
It consists of an external fibro-vascular coat, an internal coat of nucleated cells, and a transparent,
albuminous fluid in which the ovum is suspended.
The maturation of the follicle is called
folliculogenesis.
Gametes,
sperm and egg cells, are produced by the cellular division process of
meiosis.
Oogenesis is the process of meiosis for egg cell formation. It begins in the ovaries and is regulated by
follicle stimulating hormone (FSH). This hormone initiates the growth of ovarian follicles. FSH also stimulates the secretion of
estrogen from the follicle cells, promoting the maturation of the ovum.
For each primary oocyte that undergoes meiosis, only one functional egg cell is produced. The other three cells produced are called
polar bodies. Polar bodies have no function and eventually deteriorate.
A mature ovarian follicle actually contains the secondary oocyte. Unlike the sperm, the egg is arrested in the secondary oocyte stage due to oocyte maturation inhibitor (OMI) fertilization.
Upon fertilization by sperm, the secondary oocyte undergoes second meiosis and becomes a
zygote.
*
Slide at fda.gov*
Images at okstate.edu*
Life cycle at gfmer.ch*
See images of follicles in Technostorks: Award-winning documentary on Infertility and IVF
