Oogenesis

Abstract

Oogenesis is the process of formation of the mature follicle that can ovulate from the primordial follicle and takes place in the ovarian cortex. It is also called folliculogenesis, as it describes the development of an ovarian follicle that contains an immature oocyte. Folliculogenesis begins before birth, becomes active at puberty, and ends with menopause. The follicle passes through stages called primordial, primary, secondary, and Graafian, until mature follicles are formed in the ovaries. Primordial follicles consist of the primary oocyte along with a single layer of flat follicle cells surrounding it and are separated from the ovarian stroma by a basement membrane. Primary follicles are formed when the follicle cells surrounding the primary oocyte are transformed into a cubical form. Depending on the number of layers of follicular cells, there are two types of primary follicles, unilaminar and multilaminar. When the antral space begins to appear between the granulosa cells of the secondary follicle, the follicle is called a secondary oocyte. Graafian follicles, also known as mature follicles, form at the end of follicular development; these are the follicles that enter ovulation.