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An oocyte (UK: /ˈoʊəsaɪt/, US: /ˈoʊoʊ-/), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis, forming oogonia. During oogenesis, the oogonia become primary oocytes. An oocyte is a form of genetic material that can be collected for cryoconservation.

The formation of an oocyte is called oocytogenesis, which is a part of oogenesis.[1] Oogenesis results in the formation of both primary oocytes during fetal period, and of secondary oocytes after it as part of ovulation.

Oocytes are rich in cytoplasm, which contains yolk granules to nourish the cell early in development.

During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle.[2]

The only normal human type of secondary oocyte has the 23rd (sex) chromosome as 23,X (female-determining), whereas sperm can have 23,X (female-determining) or 23,Y (male-determining).

The space within an ovum or immature ovum is located is the cell-nest.[3]

The cumulus-oocyte complex contains layers of tightly packed cumulus cells surrounding the oocyte in the Graafian follicle. The oocyte is arrested in Meiosis II at the stage of metaphase II and is considered a secondary oocyte. Before ovulation, the cumulus complex goes through a structural change known as cumulus expansion. The granulosa cells transform from tightly compacted to an expanded mucoid matrix. Many studies show that cumulus expansion is critical for the maturation of the oocyte because the cumulus complex is the oocyte's direct communication with the developing follicle environment. It also plays a significant role in fertilization, though the mechanisms are not entirely known and are species specific.[4][5][6]

Because the fate of an oocyte is to become fertilized and ultimately grow into a fully functioning organism, it must be ready to regulate multiple cellular and developmental processes. The oocyte, a large and complex cell, must be supplied with numerous molecules that will direct the growth of the embryo and control cellular activities. As the oocyte is a product of female gametogenesis, the maternal contribution to the oocyte and consequently the newly fertilized egg, is enormous. There are many types of molecules that are maternally supplied to the oocyte, which will direct various activities within the growing zygote.

The DNA of a cell is vulnerable to the damaging effect of oxidative free radicals produced as byproducts of cellular metabolism. DNA damage occurring in oocytes, if not repaired, can be lethal and result in reduced fecundity and loss of potential progeny. Oocytes are substantially larger than the average somatic cell, and thus considerable metabolic activity is necessary for their provisioning. If this metabolic activity were carried out by the oocyte's metabolic machinery, the oocyte genome would be exposed to the reactive oxidative by-products generated. Thus it appears that a process evolved to avoid this vulnerability of germline DNA. It was proposed that, in order to avoid damage to the DNA genome of the oocytes, the metabolism contributing to the synthesis of much of the oocyte's constituents was shifted to other maternal cells that then transferred these constituents to oocytes.[7][8] Thus, oocytes of many organisms are protected from oxidative DNA damage while storing up a large mass of substances to nurture the zygote in its initial embryonic growth.

During the growth of the oocyte, a variety of maternally transcribed messenger RNAs, or mRNAs, are supplied by maternal cells. These mRNAs can be stored in mRNP (message ribonucleoprotein) complexes and be translated at specific time points, they can be localized within a specific region of the cytoplasm, or they can be homogeneously dispersed within the cytoplasm of the entire oocyte.[9] Maternally loaded proteins can also be localized or ubiquitous throughout the cytoplasm. The translated products of the mRNAs and the loaded proteins have multiple functions; from regulation of cellular "house-keeping" such as cell cycle progression and cellular metabolism, to regulation of developmental processes such as fertilization, activation of zygotic transcription, and formation of body axes.[9] Below are some examples of maternally inherited mRNAs and proteins found in the oocytes of the African clawed frog.

The oocyte receives mitochondria from maternal cells, which will go on to control embryonic metabolism and apoptotic events.[9] The partitioning of mitochondria is carried out by a system of microtubules that will localize mitochondria throughout the oocyte. In certain organisms, such as mammals, paternal mitochondria brought to the oocyte by the spermatozoon are degraded through the attachment of ubiquitinated proteins. The destruction of paternal mitochondria ensures the strictly maternal inheritance of mitochondria and mitochondrial DNA (mtDNA).[9]

In mammals, the nucleolus of the oocyte is derived solely from maternal cells.[22] The nucleolus, a structure found within the nucleus, is the location where rRNA is transcribed and assembled into ribosomes. While the nucleolus is dense and inactive in a mature oocyte, it is required for proper development of the embryo.[22]

Maternal cells also synthesize and contribute a store of ribosomes that are required for the translation of proteins before the zygotic genome is activated. In mammalian oocytes, maternally derived ribosomes and some mRNAs are stored in a structure called cytoplasmic lattices. These cytoplasmic lattices, a network of fibrils, protein, and RNAs, have been observed to increase in density as the number of ribosomes decrease within a growing oocyte.[23]

Female mammals and birds are born possessing all the oocytes needed for future ovulations, and these oocytes are arrested at the prophase I stage of meiosis.[24] In humans, as an example, oocytes are formed between three and four months of gestation within the fetus and are therefore present at birth. During this prophase I arrested stage (dictyate), which may last for many years, four copies of the genome are present in the oocytes. The arrest of ooctyes at the four genome copy stage appears to provide the informational redundancy needed to repair damage in the DNA of the germline.[24] The repair process used likely involves homologous recombinational repair.[24][25][26] Prophase arrested oocytes have a high capability for efficient repair of DNA damages.[25] DNA repair capability appears to be a key quality control mechanism in the female germ line and a critical determinant of fertility.[25]

The spermatozoon that fertilizes an oocyte will contribute its pronucleus, the other half of the zygotic genome. In some species, the spermatozoon will also contribute a centriole, which will help make up the zygotic centrosome required for the first division. However, in some species, such as in the mouse, the entire centrosome is acquired maternally.[27] Currently under investigation is the possibility of other cytoplasmic contributions made to the embryo by the spermatozoon.

During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centrosome, which is responsible for maintaining the microtubule system. See anatomy of sperm

GFR, estimated glomerular filtration rate, eGFR, calculated glomerular filtration rate, cGFR

This is a blood test that looks for changes in how your kidneys function. Your kidneys have tiny filters called glomeruli. The filters help remove waste from your blood. Your glomerular filtration rate is the rate at which your blood is filtered each minute. A glomerular filtration rate can be estimated with great accuracy, based on the result of other blood tests that measure serum creatinine and serum cystatin C. Other factors are used, such as your weight and age. This is called the estimated glomerular filtration rate, or eGFR.

GFR may be a urine test, but this is done only in special situations.

You may need this test to see if your kidneys are working the way they should, especially if you have diabetes or high blood pressure. GFR can detect kidney disease in its earliest stages, when it is most treatable. GFR can also help figure out if you have a condition that causes decreased blood flow to the kidneys, such as heart failure, shock, or severe fluid loss (dehydration).

Your healthcare provider is likely to order other tests that measure kidney function and waste products, such as:

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

The normal range for GFR depends on your age, weight, and muscle mass. In most healthy people, the normal GFR is 90 or higher.

Here are typical ranges:

If your test results indicate you have early kidney disease, your healthcare provider may want to take steps to treat it aggressively.

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Having a blood test with a needle has some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

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Adding a device known as a TV tuner to your computer is easy, and will cost less money than investing in a personal video recorder A computer TV tuner plugs

The bars represent frequencies of distinctive values of a variable or commonly the distinct values themselves The number of values on the x-axis of a bar graph or the y-axis of a column graph is called the scale

Tottenham defender Emerson Royal has revealed that Barcelona's financial situation was the reason for his swift exit from the Spanish giants. Linking up with Barca last summer after the club exercised their option to buy the player outright having been co-owned by them and Real Betis previously, the Brazil international made three appearances for Blaugrana in La Liga before heading to Tottenham prior to the summer transfer window slamming shut.

While it was always Emerson's intention to succeed at the Camp Nou and become a regular in the team at right-back, the player has confirmed that Barca's perilous financial situation was made clear to him upon his arrival following his switch from Betis. However, he has stated that a transfer to Tottenham was the "best option" for him.

"The club was going through a very difficult economic time and there were also good options out there for me, like Tottenham. I helped Barca and Barca helped me go to the best league in the world," the Brazilian said in an interview with Cadena SER. "I had the desire to succeed at Barca and I was going for it, but when I arrived I saw the situation at the club, they explained everything to me and in the end I understood that although it was difficult it was the best option for me."

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Emerson may have only joined Tottenham at the end of the summer transfer window but he has been linked with an exit from N17 already. Now playing second fiddle to Matt Doherty at right-back, the youngster has been linked with a return to Spain with Atletico Madrid.

"Yes, it has come to me that Atletico has been interested in me," he admitted. "But now I'm in a good moment at Tottenham, I don't know what will happen in the future. I like that the teams are watching my football."

Like a number of foreign players coming to the Premier League, Emerson has found it tough at times as he looks to get used to the pace and intensity of the top flight. Even in training the Brazil international has noticed a huge difference between how Tottenham, Barcelona and Real Betis prepare for games.

"It's very different, the Premier League is much more physical. I think the Premier is improving a lot. Very good players are arriving and you can improve your level a lot. The Premier League allows you to evolve a lot and this attracts footballers a lot," said Emerson.

"The training sessions are also different because the games require you to be at 100%. You train much more at Tottenham than at a team like Barça or Betis. In Barcelona we did more training on positions, more technique and with the ball. But in the Premier you need to work much more physically and at the moment I'm adapting very well."