Oogenesis - layers of encircling cells, now called...

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Oogenesis Oogenesis  consists of the meiotic cell divisions that lead to the production of ova (eggs) in females.  The process begins during fetal development with the fetal ovary. Diploid cells called oogonia divide  by mitosis and differentiate to produce primary oocytes (still diploid with 46 chromosomes). Each  primary oocyte is encircled by one or more layers of cells. The oocyte and encircling cells together  are called an ovarian follicle. The primary oocytes (within their follicles) begin meiosis, but division  progresses only to prophase I. They remain at this stage until puberty.  The following stages in the development of an ovarian follicle are observed:  1. The primordial follicle, the initial fetal state of the follicle, encircles the oocyte with a  single layer of cells, called follicular cells. 2. The primary follicle, the next stage of follicular development, possesses two or more 
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Unformatted text preview: layers of encircling cells, now called granulosa cells. 3. The secondary follicle is distinguished by the presence of the antrum, a fluid-filled, central cavity. 4. In a mature (vesicular, or Graafian) follicle, the primary oocyte has completed meiosis I. It is the stage of follicular development that precedes ejection of the oocyte from the ovary (ovulation). The following features are observed: 1. The zona pellucida, a clear layer of glycoprotein, surrounds the oocyte. 2. The corona radiata, a ring of granulosa cells, encircles the zona pellucida. 3. Several layers of cells (theca cells) surround the granulosa cells. 5. The corpus luteum is the remains of the follicle following ovulation. It remains functional, producing estrogen, progesterone, and inhibin, until it finally degenerates....
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