The main female reproductive organs, or gonads, room the two ovaries. Each ovary is a solid, ovoid structure about the size and also shape of one almond, around 3.5 cm in length, 2 cm wide, and 1 cm thick. The ovaries are located in shallow depressions, referred to as ovarian fossae, one on each side that the uterus, in the lateral walls of the pelvic cavity. They are held loosely in place by peritoneal ligaments.

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Structure

The ovaries space covered top top the exterior by a great of straightforward cuboidal epithelium dubbed germinal (ovarian) epithelium. This is actually the visceral peritoneum the envelops the ovaries. Underneath this class is a thick connective organization capsule, the tunica albuginea. The substance of the ovaries is distinctly separated into an external cortex and also an inner medulla. The cortex appears an ext dense and granular due to the visibility of numerous ovarian follicles in miscellaneous stages the development. Each of the follicles has an oocyte, a woman germ cell. The medulla is a loose connective organization with plentiful blood vessels, lymphatic vessels, and also nerve fibers.

Oogenesis

Female sex cells, or gametes, construct in the ovaries by a form of meiosis dubbed oogenesis. The sequence of occasions in oogenesis is comparable to the succession in spermatogenesis, however the timing and also final an outcome are different. Early in fetal development, primitive germ cell in the ovaries identify into oogonia. This divide swiftly to type thousands of cells, still referred to as oogonia, which have a full match of 46 (23 pairs) chromosomes. Oogonia then enter a expansion phase, enlarge, and become major oocytes. The diploid (46 chromosomes) main oocytes replicate their DNA and also begin the an initial meiotic division, but the procedure stops in prophase and the cells remain in this rely state till puberty. Plenty of of the major oocytes degenerate before birth, but even with this decline, the 2 ovaries with each other contain approximately 700,000 oocytes at birth. This is the lifetime supply, and no more will develop. This is quite different than the masculine in i beg your pardon spermatogonia and also primary spermatocytes proceed to be produced throughout the reproductive lifetime. Through puberty the variety of primary oocytes has further decreased to around 400,000.

Beginning at puberty, under the influence of follicle-stimulating hormone, several major oocytes start to flourish again each month. One of the major oocytes appears to outgrow the others and it resumes meiosis I. The various other cells degenerate. The big cell experience an unequal department so that virtually all the cytoplasm, organelles, and fifty percent the chromosomes walk to one cell, which becomes a an additional oocyte. The remaining half of the chromosomes go to a smaller cell referred to as the an initial polar body. The second oocyte begins the second meiotic division, however the procedure stops in metaphase. In ~ this point ovulation occurs. If fertilization occurs, meiosis II continues. Again this is an unequal department with every one of the cytoplasm going come the ovum, which has 23 single-stranded chromosome. The smaller cell native this department is a second polar body. The an initial polar body likewise usually divides in meiosis ns to create two even smaller polar bodies. If fertilization does not occur, the 2nd meiotic division is never completed and the second oocyte degenerates. Right here again there are evident differences in between the male and also female. In spermatogenesis, 4 functional sperm build from each main spermatocyte. In oogenesis, only one sensible fertilizable cell develops from a major oocyte. The other three cells are polar bodies and also they degenerate.

Ovarian Follicle Development

An ovarian follicle consists of a occurring oocyte surrounding by one or much more layers the cells dubbed follicular cells. At the exact same time that the oocyte is proceeding through meiosis, corresponding alters are following in the follicular cells. Primordial follicles, which consist of a main oocyte surrounding by a solitary layer of planarization cells, build in the fetus and also are the stage that is present in the ovaries in ~ birth and throughout childhood.

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Beginning in ~ puberty, follicle-stimulating hormone stimulates changes in the primordial follicles. The follicular cells come to be cuboidal, the primary oocyte enlarges, and also it is now a major follicle. The follicles proceed to grow under the influence of follicle-stimulating hormone, and the follicular cells proliferate to kind several class of granulose cells roughly the major oocyte. Many of these main follicles degenerate along with the major oocytes within them, however usually one proceeds to develop each month. The granulosa cells begin secreting estrogen and also a cavity, or antrum, forms within the follicle. Once the antrum starts to develop, the follicle becomes a an additional follicle. The granulose cells also secrete a glycoprotein problem that develops a clean membrane, the zona pellucida, around the oocyte. After around 10 work of development the follicle is a maturation vesicular (graafian) follicle, which creates a "blister" top top the surface of the ovary and also contains a an additional oocyte all set for ovulation.

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Ovulation

Ovulation, motivated by luteinizing hormone native the anterior pituitary, occurs when the mature follicle in ~ the surface ar of the ovary ruptures and also releases the an additional oocyte right into the peritoneal cavity. The ovulated second oocyte, all set for fertilization is still surrounded by the zona pellucida and a couple of layers of cells dubbed the corona radiata. If it is not fertilized, the secondary oocyte degenerates in a couple of days. If a sperm passes v the corona radiata and also zona pellucida and also enters the cytoplasm that the second oocyte, the 2nd meiotic division resumes to type a polar body and a maturation ovum

After ovulation and in response to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and also is transformed into a body luteum. The body luteum is a glandular structure that secretes progesterone and also some estrogen. The fate relies on whether fertilization occurs. If fertilization does no take place, the corpus luteum remains sensible for about 10 days; then it begins to degenerate into a corpus albicans, i beg your pardon is mainly scar tissue, and also its hormone calculation ceases. If fertilization occurs, the body luteum persists and continues that hormone functions until the placenta establishes sufficiently to secrete the crucial hormones. Again, the corpus luteum at some point degenerates into corpus albicans, but it remains practical for a longer period of time.