Fig. 10

Drawing diagram showing the follicular development and follicular stages in sheep ovary. Preantral phase: Formation of primordial follicles which present in nests; Primordial follicle has a single layer of flattened follicular cells. Follicular activation of the primordial follicles to form unilaminar primary follicles; unilaminar primary follicle has a single layer of cuboidal follicular cells. Then growth of unilaminar primary follicles to form multilaminar primary follicles; multilaminar primary follicles have several layers of granulosa cells and few theca cells. All the preantral follicles have a primary oocyte surrounded by follicular cells and separated from the follicular cells by increased thickness zona pellucida. Antral phase: Follicle growth continues through the phases of recruitment, selection, dominance, and preovulatory stage of follicular waves. Secondary follicle has several layers of granulosa cells with small accumulations (pools) of follicular fluid in the intracellular spaces and a small number of theca cells. Tertiary follicle has several granulosa cell layers, corona radiata, cumulous oopherous, theca folliculi, and primary oocyte and is characterized by a single large antral cavity which contains follicular fluid. Preovulatory (Mature Graafian) follicle is the last stage of follicle development; these follicles are larger, have more antral fluid and may contain a secondary oocyte and protrude from ovarian surface epithelium and separated from them by very thin layer of granulosa cells and tunica albuginea. Ovulatory follicle is preovulatory from which the ovum and its surrounding cells released to the peritoneal catvity by rupture of the thin follicular wall