Definition - What does Primary Follicle mean?
A primary follicle is an immature follicle in the ovary consisting of an egg (oocyte) surrounded by a single layer of square-shaped supporting cells that protect the egg and receive signals for further development. The primary follicle is the second stage of follicle development in the ovary and occurs when a primordial follicle is recruited for development and maturation in preparation for eventual ovulation.
FertilitySmarts explains Primary Follicle
Formation of the primary follicle occurs when a primordial follicle, which is the most immature form of a follicle, is recruited for further development. The single layer of flat cells that surround a primordial follicle receive signal and initiate a change into a square shape. As these cells are activated they also establishe surface receptors for follicle-stimulating hormone (FSH) in preparation to receive further signals for follicular maturation.
In addition to the changes in the outer cell layer, the egg cell itself begins to undergo an early maturation process. Genes are activated in the nucleus of the egg that trigger the formation of a protein coat that will become the zona pellucida which will encapsulate the egg. This coat will become important as the activated sperm will need to go through the zona pellucida to fertilize the fully matured egg.