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Oocyte

Oocyte

Egg (oocyte)The oocyte (eggs, ova, ovum) is arrested at an early stage of the first {{meiosis)) (first meiotic) division as a primary oocyte (primordial follicle) within the ovary. Following puberty, during each menstrual cycle, pituitary gonadotropin stimulates completion of meiosis 1 the day before ovulation. Early oocytes are also classified as immature (germinal vesicle (GV) or metaphase I (MI) stage). The breakdown of the germinal vesicle indicates a resumption of meiosis and the extrusion of the first polar body (1 PB) indicates completion of the first meiotic division in human oocytes.

The released oocyte is surrounded by a thick specialized extracellular matrix, the zona pellucida that in turn is covered in layers of cells, the granulosa layer.In an adult human female, the development of a primordial follicle containing an oocyte to a preovulatory follicle takes in excess of 120 days.