Yesterday, we posted a “mysterious” photo on our Facebook page. Did you answer correctly?
This is a high magnification of a small part of a mammalian ovary showing a primordial follicle on the left and a primary follicle on the right. The large egg cell (oocyte) can be seen in each follicle surrounded by a single thin layer of follicular cells in the primordial follicle and several layers of larger follicular cells in the primary follicle.
One can easily see the voluminous cytoplasm, large nucleus, and dark round nucleolus in each egg. When a human baby girl is born she will already have a fixed number of about 400,000 primordial follicles which do not begin to mature until she reaches sexual maturity. Then every 28 days about 40 primordial follicles begin to mature and enlarge to become the first primary follicles.
Typically only one forms the large Graafian follicle which ovulates releasing an egg into the oviduct where it may be fertilized. The other follicles in the cohort break down by a process called atresia. About 500 eggs (ova) are ovulated during the reproductive life of a typical woman.
For more details on this marvelous process of the development of the eggs, fertilization, implantation, and development of the placenta, see Dr. David Menton’s bestselling DVD, Fearfully and Wonderfully Made.