Oocyte primary oocyte secondary oocyte egg cell
Oocytes, i.e. primordial germ cells, occur during the female embryonic period, are present in the ovaries and can undergo mitosis for quantitative expansion.
The proliferation of egg cells occurs only during the fetal period and ends at birth. That is, how many egg reserves a woman has in her lifetime is predestined before birth.
Oocytes also differentiate into primary oocytes during proliferation. Once it differentiates into a primary oocyte, it cannot multiply in number, after which it can only undergo meiosis, after which it can form 1 egg cell after two meiosis. That is, 1 primary oocyte can only evolve into 1 egg cell. One egg protocelle has the opportunity to evolve into many egg cells.
Primary oocytes are derived from the differentiation of oocytes. The egg protocells enter the 4-fold state through DNA synthesis, instead of mitosis, and when they are quiescent, they form primary oocytes. At this time, it will no longer be able to undergo mitosis, but will just wait quietly and enter a long period of dormancy. When will it wake up? Until the follicles recruit and begin to develop the follicles, the first deceleration division is carried out, forming a huge secondary oocyte and a small polar body. Half of the genetic material carried by the polar body is discarded, while the secondary oocytes carry the other half of the genetic material and a large number of organelles and cytoplasm waiting for the next transformation. We often say that the basal follicle refers to the primary oocyte, which is a basic follicular unit.
Because the mitosis of egg protocells is stopped at birth, from birth, the stock reserves of the female ovaries can only become smaller and less, and it is impossible to increase. And the rate of reduction is faster than the average person imagines.
The number of germ cells in women peaks at 20 weeks of fetal age, with about 6 to 7 million (about 1/3 of the oocytes, 2/3 of the primary oocytes). Why are there no secondary oocytes? Because secondary oocytes occur during the ovulation phase). As the oocytes continue to proliferate, a large number of primary oocytes (primordial follicles) are gradually atresia. At birth, germ cell reserves plummeted to about 2 million. The atresia continues in childhood, with about 300,000 eggs left before puberty begins. Because women can only release one egg a month, only about 400 eggs will eventually have the opportunity to develop into egg cells.
Secondary oocytes, which are derived from the first meiosis of primary oocytes, are 2ploids, which contain two monomeric genetic materials. Secondary oocytes appear 36 to 48 hours before ovulation, during the first meiosis period.
Egg cells, derived from secondary egg cells through a second meiosis, are haploids that contain only 1 monomer of genetic material. Born in the fallopian tubes, before fertilization. During the second meiosis, the secondary oocytes split in two to form a giant egg cell and a very small second polar body. Egg cells contain the cytoplasm and organelles of almost all secondary oocytes, as well as 1 monomeric piece of genetic material. The second polaroid, on the other hand, takes away only another portion of the monomeric genetic material.
Next, I need to ask you 1 question
When a woman goes to see infertility, the doctor will check her ovarian reserve, is it the ovarian reserve, or the primary oocyte reserve, or the secondary oocyte reserve?
A. Oocyte reserve
B. Primary oocyte reserve
C. Secondary oocyte reserve
D. Egg cell reserve
E. Oocyte and primary oocyte reserve
From this article, we can see that primary oocytes go through a long hibernation to wait for the moment of ovulation. How long will it take?
Suppose a woman begins ovulating at the age of 15, menopause at the age of 50, and has a fertility period of 35 years. Then the primary oocytes with the shortest dormancy wait about 15 years, and the primary oocytes that dormant for the longest time wait about 50 years. Why about it? Because we don't know when this primary oocyte was formed before birth.
From this we can extend some knowledge. In terms of egg quality, what is the age at which a woman is most likely to have children? We are not going to discuss the optimal age for childbearing here, because discussing this will definitely be scolded.
Theoretically, if a woman starts ovulating at age 15 and goes to menopause at age 50, the age at which a woman is most likely to conceive and have children is 15. Because the primary oocytes of this period have only been dormant for 15 years, they are the freshest eggs, they have not experienced so much wind and rain, and both organelles and genetic material have the best vitality. The older you get, the older the eggs get and the worse the quality of your eggs.
It is easier to understand why the incidence of fetal arrest in the first trimester of pregnancy increases with age, why the incidence of infertility increases with age, and why the success rate of IVF is more difficult to succeed the older you get.
When IVF is infancy, we are very concerned about the number of sinus follicles, and the larger the number of follicles, the more opportunities there are, the more opportunities there are. But age determines the quality of the sinus follicles, and the older the age, the worse the quality. So, sometimes, the number of sinus follicles goes up, and the success rate is still very low. The success rate of a 40-year-old woman who induces ovulation to obtain 20 eggs may not be able to match the success rate of a 30-year-old woman who induces ovulation to obtain only 10 eggs.
A 25-year-old woman, because of the malignant tumor of the ovaries, removed most of the ovaries, two years later still successfully pregnant and gave birth to a child, even if she soon had premature ovarian failure in the next 5 years, it still did not hinder her fertility efficiency, why, because of youth. And a 35-year-old woman, because of ordinary ovarian cysts, doctors carefully protect the ovarian cortex, preserve her fertility reserves, postoperative examination of ovarian reserves is indeed very good, and eventually she did not get pregnant naturally, why, because of age.
There is no standard answer to the next multiple choice question
What do you think is the best age for a woman to have children?
A.18~25岁
B. 22 to 28 years old
C. 25 to 30 years old
D. 28 to 32 years old
E.30~35岁
F. The old lady is willing, it's a matter of you!
According to the National Bureau of Statistics, the average age of Chinese women who have a third child or more is about 31:00 years old, not more than 32 years old. This data has not fluctuated significantly from 1978 to 2000, to 2015, and then to 2018, and has always remained in the range of 31 to 32 years old, not more than 32 years old. This means that for most women who have children after the age of 32, your fetus is most likely your last. We can also conclude that if you want to have more than one child in this lifetime, you should do so before the age of 32, no matter how many. Because at the age of 32, it may already be the last child for most women.
I hope that this article can make young girls, as well as parents who are raising girls, see that women should plan their fertility reasonably so as not to leave lifelong regrets.
Finally, one more question for everyone
What are the eggs that are released during ovulation?
A. Oocytes
B. Primary oocytes
C. Secondary oocytes
D. Egg cells
E. Polar body