How Are Primary & Vesicular Follicles Different?

A follicle is defined as any small spherical group of cells containing a cavity that allows another structure to grow within it. The general difference between a primary follicle and a vesicular follicle is that the primary follicle contains an oocyte that is not fully formed or at the point of maturation for the ovulatory phase of a woman's cycle, whereas the vesicular follicle contains an almost fully realized ovum.

Function

• Ovarian follicles are essential to the developing gamete (the reproductive cell that contains one set of chromosomes), as well as its corresponding follicular cells. Both primary and vesicular follicles are a part of the process leading up to the maturation of an ovum. In the progression of follicle formations, the primary follicle goes through mitosis to create other follicular cells and forms several layers surrounding the oocyte. The number of cells will augment, causing estrogen to be released. Throughout this cycle, certain primary follicles will go on to transform into vesicular follicles, which are paramount to the pre-ovulatory phase.

Process

• There are several phases in the eventual formation of both primary and vesicular follicles. These follicles are generated by the secretion of gonadotropic hormones and luteinizing hormones. Once this happens, the primordial follicle is born, possessing an oocyte that emits yolk granules, causing the follicular cells to alter in appearance from being flattened to the cube-like or columnar shape that characterizes the primary follicle. The primary follicle turns into the secondary follicle, where the membrana granulosa are present and start to secrete follicular fluid that will eventually lead to the next step in the follicular development process, the vesicular follicle.

Features

• A primary follicle includes a single oocyte that possesses a layer of cube-like and columnar cells. A vesicular follicle has a membrana granulosa, which is a membrane that exists within larger ovarian follicles that consist of an external fibrovascular coat and an internal coat that has layers of nucleated cells, or the membrana granulosa. Pockets of follicular fluid in the membrana granulosa indicate one of the traits of a vesicular follicle. As the vesicular follicle's development continues, the individual pockets join together to forge a large, fluid-filled pocket, known as the follicular antrum.

Misconceptions

• Although the vesicular follicle has an oocyte, which is considered a mature egg, the follicle does not release an actual ovary. The ovary itself is what releases the oocyte at the end of a menstrual cycle.

Significance

• Without the important operations carried out by the primary and vesicular follicles, a woman's pre-ovulatory phase would be in complete disarray. Each of these follicles are absolutely paramount to the eventual ejection, through menstruation, of the ovum from the ovary.