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Oocyte ‒ compendium of definitions, concepts and meanings
Definition of oocyteAn oocyte, oocyte or ocytus, is a female gametocyte or germ cell involved in reproduction. In other words, is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cells (PGC), which undergo meiosis to form an oogonio. During the oogenesis of the oogonio, it becomes a primary oocyte (in situ pronounced oh' to), which is a female germ cell that is in the process of becoming a mature egg. In general it is an egg released by the ovary in each ovulacion.1
The formation of an oocyte is called oogenesis or ovocitogenesis and is a form of gametogenesis, whose male counterpart is spermatogenesis.
The ovocitogenesis ends in the formation of both primary before birth oocytes and secondary oocytes after birth, as part of ovulation.
The maturation of the oogonium, egg precursor cell, will result in the primary oocyte. This process is carried out during embryonic development, so the number of oocytes is determined before birth (some two million approximately); It is what is called ovarian reserve.
The oocyte enters meiosis before birth, stopping at Prophase I until the entry into puberty. After the resumption of the division, the primary oocyte increases in size. Completes the first meiotic division and obtained two unequal cells: the secondary oocyte, which receives most of the cytoplasm, and the first corpuscle polar, non-functional small cell that degenerates soon.
The secondary oocyte starts the second meiotic division, which will only be completed if fertilization occurs. It would be generated then the Zygote and the second polar corpuscle. If fertilization does not occur, the second meiosis stops at metaphase.
Of the 400,000 oocytes can be in puberty, only some 400 will become secondary oocyte and they ovularán. The rest will enter into atresia.
In humans, ploidy has n = 23, with duplicated chromosomes.
Concept of oocyteThe oocytes are female germ cells that are generated in the ovaries. It is a phase of the development of the egg, when it has not yet matured. The oocyte emerges as part of the process of gametogenesis that develops in women and in the females of animals.
The procedure begins with a primordial germ cell that becomes an oogonio through meiosis. This oogonio after the oogenesis becomes an oocyte that will finally result in mature unovulo. The menstrual cycle is that these eggs shed ovaries every 28 days from puberty until menopause.
The oocyte, which also receives the name of ocytus uoocito, it is therefore a female cell that is on its way to becoming a mature egg. This kind of cell has a good level of cytoplasm that allows you to contribute to the cellular nutrition at the beginning of the development.
It is important to note that the amount of oocytes that have a woman as it is defined before its birth, as set out in fetal development. With over the years, women will be losing oocytes in a phenomenon known as atresia. Menstruation makes that the oocyte to develop and, in turn, Miss: reached 35 years of age, women will have about 10% of the ocitos that was born, a circumstance that makes more complicated to achieve fertilization and that the health risks are increased in the unborn child.
Meaning of oocyteFemale germ cell that is in the process of becoming a mature egg. To do this, it will be necessary to carry out a complex process of cell division called meiosis with the aim of halving its chromosomal complement.
Its function is the formation of a Zygote to merge your kernel with the male gamete (spermatozoon), phenomenon called fertilization.
The woman is born with an already established endowment of oocytes that are progressively disappearing due to a phenomenon called atresia, so that upon reaching the age of puberty are approximately about 300,000 oocytes in the ovaries. In each menstrual cycle, an egg will run until ovulation and about 1,000 will be lost. In this way, at the age of 35 are aproximadadamente 10% of the oocytes. Less oocytes are worse is its quality.
It is common that in cases of age maternal advanced already is exhausted the ovarian reserve able to give rise to a healthy child.
A chromosome study of oocytes requires biopsy of polar corpuscle with further analysis.
Definition of oocyteOocyte maturation
Germ cells begin to differentiate themselves from the embryonic life, a series of cells will develop from day 24 of the embryonic development reaching the outlines of genitals, ovaries, from there begin to divide by mitosis in cells called oogonia. Germ cells begin to differentiate into oogonia, cells that will continue to develop to form oocytes, these oogonia in the third month of embryonic life begin to surround himself with a flattened cells called follicular cells. These oogonia in the sixth month of embryonic development are no longer divided by mitosis meiosis beginning. Cells that divide by meiosis, meiotic first division, are forming the primary oocyte, so the oogonia become the primary oocyte. This primary oocyte starts split becoming paralyzed in the first meiotic prophase, the first meiotic division, in particular at a stage which is called diplotene.
In first prophase, meiotic there are several stages, in which occurs the intermingling of the genetic material of the chromosomes, genetic recombination. In the diplotene phase the genetic material is not very condensed, by which the cell can keep for a long time, since it allows the transcription of various genes to maintain the living cell and for a long time.
The oocyte arrested in diplotena is surrounded by flattened cells, follicular cells. Called to the set of the primary oocyte that has entered meiosis and follicular cells primary follicle. The primordial follicles are formed in the embryo age and will keep in the sketches of the ovaries and after the birth of the ovaries remain as primordial follicles that are within the structure of the ovary.
The ovary has almond-shaped (3.5 cm - 5 cm long) that has a layer of connective tissue the outermost part that is called the tunica albuginea, located inside a very vascularized tissue that form the tunica vasculosa, highly irrigated, and the primordial follicles are among this tunic stockings. The primordial follicle from birth begins to differentiate themselves, as these are the first steps in the oocyte differentiation independent of the hormonal contribution, the primordial follicles are going to become primary follicles in which follicular cells divide forming one layer of square cells that are still surrounding the primary oocyte, who remains detained at the first meiotic division, these follicular cells are transformed into other types of cells called cells granular. After a layer of cells is formed granular, these cells begin to divide and form several layers of cells granular to retrieve the oocyte. So the primary follicle is called follicle growth, since it is growing. Here is where you can reach the follicle without hormonal contribution, therefore in an ovary on which we do not have hormonal contribution cannot be primordial follicles, primary follicles, or follicles in growth. The mitosis arrested in diplotena but there are changes within your structure, they begin appear microvilli that begin to ascend to the surface of the primary oocyte. Also appears a substance formed by mucoproteinas that accumulate the microvilli and called the zona pellucida. Granular so the zona pellucida are mucopolysaccharides that are surrounding the primary oocyte and that accumulate between microvilli, the zona pellucida is located between the surface of the primary oocyte and the cells that they are surrounding the oocyte, this happens at the stadium of follicle growth. At the same time of the formation of the zona pellucida, also displayed a number of vesicles which come from the complex of Golgi, which stood below the plasma membrane at the periphery of the primary oocyte called cortical granules which will have an important role in fertilization. Oocyte further complicated its structure through the formation of a layer of cells that will surround the follicle growth, are part of that follicle, this group of cells around the cells granular and called the teak (teak is a cellular structure that resort to all granular and therefore the primary oocyte, surrounds the cells granules by the outermost cells)(, they grow by dividing by mitosis) teak has two very important functions: has specific receptors for the hormones FSH and LH that will control the maturation of the follicle and the entire process of ovulation. These hormones did not have any influence on the development of follicles since there was no structure that would have receptors for these hormones. By which growth has been independent of the hormonal contribution. From the moment that appears teak, which contains receptors in the membrane, so the maturation of the follicle will be determined by the appearance of the hormones, appearing in a cyclic way, which causes a cyclic maturation of follicles. Other function resides in the inner layer of teak, highly vascularized area, cells secrete estrogen specifically estradiol, which is going to secrete into the bloodstream, hormones that also will control and mature the follicle for to continue the development of the oocyte and can form the secondary oocyte.
Therefore until this moment we have the primary oocyte arrested in diplotena, granular cells and teak and all this forms the follicle growth, until this moment the follicle matured independently to the hormonal contribution and they mature from primordial follicle to follicle growth. From this moment on which appears the teak, only some few follicles in growth of 5 to 10 will continue ripening each menstrual cycle. In the moment in which appears in the bloodstream LH and FSH hormones, makes that ovary a few follicles in growth continue to mature, but only one reaches the follicle of Degraff, which is the next stage, is going to produce the ovulation of oocyte that goes out of the ovary into the fallopian tube.
Therefore only mature 5 follicles in growth, the next stage would be the oocyte arrested in diplotena, surrounded by the zona pellucida, granular layers of cells and in the most external part teak. When the granular layers area reaches a size of 12 layers begin to open between cells granular spaces that are quickly filled by a liquid is secreted by cells granular. Spaces are becoming increasingly large and are forming a cavity inside this structure of granulosa cells, growth is called up to cavity located in the follicle follicular antrum, fluid secretion is growing and the cavity is growing more, what makes that he creates a push of the oocyte with its zona pellucida towards a more lateral zonei.e. the oocyte is located on one side, that becomes a new structure called a follicle of Degraff. Degraff follicle is one of those follicles in growth thanks to the hormonal contribution reaches upper Stadium.
In this maturing a few follicles compete with each other, by growth factors that are going to carry out the maturation of the follicle, this is what allows a single follicle reach form the follicle of Degraff. Within this follicle is where will complete mature primary oocyte, continuing the first meiotic division, which is an asymmetric division, since the two cells that are formed are not equal, appears a second large cells that is the secondary oocyte and a small cell trapped by the zona pellucida and layers that are surrounding the oocyte and is called first polar corpuscle granular. The secondary oocyte starts immediately the second meiotic division but not finish it, remains detained at second metaphase, with all chromosomes in the metaphase plate. Only to continue this second meiotic division and will be terminated if it is fertilized.
Due to the pressure of the liquid of the follicular antrum and due to the increase of luterizante hormone, LH, blood, Degraff follicle rupture occurs and takes out ovulation, which consists of the rupture of the follicle of Degraff, appears first an outgoing, stigma, which subsequently breaks out the secondary oocyte in metaphase two, the first polar corpuscleboth structures surrounded by zone pellucid and finally cell granular are surrounding the oocyte, and that from this moment, where they exit Degraff follicle passes to dominate the structure radiated Crown.
The follicle is located very near the surface of the ovary to make in rupture of the follicle Degraff to leave the secondary oocyte and the first polar body with the zona pellucida and the Crown radiated outwards from the ovary. (Only a gamete that can be fertilized, as opposed to the formation of spermatozoa forming four gametes formed.) When that occurs the ovilacion the fallopian tube is near the ovary there is a continuity, but the oocyte has to make a jump from the ovary from which is expelled until he is attracted by the movement of the liquid that is in motion by ciliated cells of fallopian tube. This flow of liquid attracts the oocyte where it will be transported along with the liquid for a subsequent fertilization. The process of adjustment is therefore exit the oocyte from the ovary to the fallopian tube.
The rest of the structure forming the oocyte, granular cells and teak, change your activity accumulated lipid and cholesterol, becoming a granular structure that it is called the corpus luteum (teak and cells granular, structure of the follicle of Degraff which has remained within the ovary after the expulsion of the secondary oocyte and first polar corpuscle surrounded by the zona pellucida and radiated Crown). This corpus luteum is to secrete hormones estradiol, that secretaba already teak and another hormone which is progesterone during a series of days, to prepare all the female genital tract, if there is a possible fertilization, and embryo development occurs in this way. So yellow body, or corpus luteum is a gland that secret hormones. If the egg is not fertilized the corpus luteum in two weeks stops secreting progesterone degenerates and becomes the body albicanis, which has no function in the development of oocytes.