When there is more than one layer of cells surrounding the primary oocyte the cells are called granulosa cells instead of follicular cells. The granulosa cells produce the female sex hormones called estrogens. Secondary follicle The granulosa cells of the primary follicle continue to divide and begin to produce a fluid. As the fluid produced by the granulosa cells builds up it comes to occupy a central region in the follicle called an antrum.
When the follicle has an antrum it is called a secondary follicle. The secondary follicle continues to grow as the fluid continues to build up until the follicle produces a noticeable bulge on the surface of the ovary. The follicle is now ready to burst and is called a mature follicle. Ovulation Human ovulation captured on film The mature follicle bursts when there is a sudden upsurge in the secretion of luteinizing hormone LH by the pituitary gland.
Just prior to bursting the primary oocyte completes the first division of meiosis. However, the division is unequal and produces a large secondary oocyte and a smaller polar body that contains primarily the nucleus. The secondary oocyte, with granulosa cells that immediately surround it called the corona radiata , is ejected into the peritoneal cavity in the process called ovulation. Corpus luteum. After the follicle ruptures the granulosa cell become transformed into cells dedicated to producing steroid hormones, in particular, progesterone.
Progesterone is the hormone that maintains the pregnancy if the secondary oocyte is fertilized by a sperm cell. Uterine Fallopian Tubes The uterine tubes form the initial part of the duct system through which the gametes travel.
The alkaline seminal fluid temporarily neutralizes the normal acidity pH 4. The composition of cervical mucus changes during menstrual cycle. Sperm can most easily penetrate the thinner E-mucus that predominates during the last few days before ovulation, as opposed to the thicker G-mucus. Two modes of transport:. Slow — the rest of the sperm swim their way up the last part of the cervical tube, are stored in cervical crypts folds of the cervix , and are slowly released into the uterus over days.
Table 2 - Karyotypes of Germ Cells and Gametes. Primordial germ cell. Primary oocyte. Secondary oocyte. Mature oocyte. Type A spermatogonium. Type B spermatogonium. Primary spermatocyte. Secondary spermatocyte. Aneuploidy is an abnormal number of chromosomes that can result from either unbalanced chromosomal translocations or nondisjunction during meiosis II.
Review articles on Oogonium. Powerpoint slides on Oogonium. Images of Oogonium. Photos of Oogonium. Videos on Oogonium. Cochrane Collaboration on Oogonium. Bandolier on Oogonium. TRIP on Oogonium. Ongoing Trials on Oogonium at Clinical Trials. Trial results on Oogonium. Clinical Trials on Oogonium at Google. FDA on Oogonium. CDC on Oogonium. Books on Oogonium. Oogonium in the news. Be alerted to news on Oogonium. Oogenesis occurs in the outermost layers of the ovaries.
As with sperm production, oogenesis starts with a germ cell, called an oogonium plural: oogonia , but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo. The cell starting meiosis is called a primary oocyte. This cell will begin the first meiotic division, but be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage.
At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell.
This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct.
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