The primary female reproductive organs, or gonads, space the two ovaries. Every ovary is a solid, ovoid structure about the size and also shape of an almond, around 3.5 centimeter in length, 2 centimeter wide, and also 1 cm thick. The ovaries are located in shallow depressions, dubbed ovarian fossae, one on each side the the uterus, in the lateral wall surfaces of the pelvic cavity. Castle are held loosely in place by peritoneal ligaments.

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Structure

The ovaries space covered on the exterior by a layer of simple cuboidal epithelium referred to as germinal (ovarian) epithelium. This is in reality the visceral peritoneum that envelops the ovaries. Under this layer is a thick connective tissue capsule, the tunica albuginea. The substance of the ovaries is distinctly divided into an external cortex and an inner medulla. The cortex appears much more dense and granular as result of the visibility of numerous ovarian follicles in assorted stages that development. Every of the follicles includes an oocyte, a mrs germ cell. The medulla is a loosened connective tissue with numerous blood vessels, lymphatic vessels, and also nerve fibers.

Oogenesis

Female sex cells, or gametes, build in the ovaries through a type of meiosis dubbed oogenesis. The sequence of events in oogenesis is similar to the sequence in spermatogenesis, however the timing and also final an outcome are different. At an early stage in fetal development, primitive germ cells in the ovaries differentiate into oogonia. These divide rapidly to kind thousands that cells, still called oogonia, which have a full enhance of 46 (23 pairs) chromosomes. Oogonia then get in a growth phase, enlarge, and become primary oocytes. The diploid (46 chromosomes) primary oocytes replicate their DNA and begin the very first meiotic division, yet the process stops in prophase and also the cells stay in this exposed state till puberty. Plenty of of the main oocytes degenerate prior to birth, however even through this decline, the two ovaries together contain about 700,000 oocytes in ~ birth. This is the lifetime supply, and no much more will develop. This is quite different than the masculine in which spermatogonia and primary spermatocytes proceed to be produced throughout the reproductive lifetime. Through puberty the variety of primary oocytes has further decreased to about 400,000.

Beginning at puberty, under the affect of follicle-stimulating hormone, several primary oocytes start to thrive again every month. Among the primary oocytes seems to outgrow the others and also it resumes meiosis I. The various other cells degenerate. The big cell experience an unequal department so that practically all the cytoplasm, organelles, and fifty percent the chromosomes walk to one cell, which i do not care a second oocyte. The remaining fifty percent of the chromosomes go to a smaller cell dubbed the first polar body. The second oocyte starts the 2nd meiotic division, but the process stops in metaphase. At this suggest ovulation occurs. If fertilization occurs, meiosis II continues. Again this is an unequal department with all of the cytoplasm going to the ovum, which has 23 single-stranded chromosome. The smaller cell from this department is a 2nd polar body. The an initial polar body likewise usually divides in meiosis i to produce two also smaller polar bodies. If fertilization does not occur, the second meiotic division is never ever completed and also the an additional oocyte degenerates. Here again over there are apparent differences between the male and female. In spermatogenesis, 4 functional sperm build from each major spermatocyte. In oogenesis, just one functional fertilizable cell develops from a main oocyte. The various other three cells room polar bodies and they degenerate.

Ovarian Follicle Development

An ovarian follicle consists of a arising oocyte surrounded by one or more layers that cells called follicular cells. In ~ the exact same time the the oocyte is advancing through meiosis, corresponding alters are following in the follicular cells. Primordial follicles, i beg your pardon consist that a primary oocyte surrounding by a single layer of planarization cells, build in the fetus and also are the stage that is present in the ovaries at birth and throughout childhood.

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Beginning at puberty, follicle-stimulating hormone stimulates transforms in the primordial follicles. The follicular cells become cuboidal, the major oocyte enlarges, and it is now a main follicle. The follicles proceed to prosper under the influence of follicle-stimulating hormone, and also the follicular cell proliferate to kind several layers of granulose cells about the main oocyte. Many of these major follicles degenerate along with the major oocytes within them, however usually one proceeds to build each month. The granulosa cells start secreting estrogen and also a cavity, or antrum, creates within the follicle. Once the antrum starts come develop, the follicle becomes a an additional follicle. The granulose cells also secrete a glycoprotein problem that forms a clear membrane, the zona pellucida, approximately the oocyte. After around 10 days of expansion the follicle is a maturation vesicular (graafian) follicle, which develops a "blister" ~ above the surface of the ovary and also contains a secondary oocyte all set for ovulation.

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Ovulation

Ovulation, prompted by luteinizing hormone native the anterior pituitary, occurs as soon as the mature follicle at the surface of the ovary ruptures and releases the second oocyte right into the peritoneal cavity. The ovulated second oocyte, all set for fertilization is still surrounding by the zona pellucida and a few layers the cells called the corona radiata. If it is no fertilized, the an additional oocyte degenerates in a pair of days. If a sperm passes with the corona radiata and also zona pellucida and enters the cytoplasm the the second oocyte, the second meiotic division resumes to kind a polar body and also a mature ovum

After ovulation and also in solution to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and also is transformed right into a body luteum. The body luteum is a glandular framework that secretes progesterone and also some estrogen. The fate depends on even if it is fertilization occurs. If fertilization does no take place, the corpus luteum remains functional for about 10 days; then it begins to degenerate into a corpus albicans, i m sorry is mostly scar tissue, and its hormone calculation ceases. If fertilization occurs, the body luteum persists and also continues that hormone features until the placenta establishes sufficiently to secrete the essential hormones. Again, the corpus luteum at some point degenerates right into corpus albicans, however it remains useful for a longer period of time.