The issues of conception, pregnancy and its development at all times rightfully top TOPs of women's topics. And, paradoxically, however, knowledge about the foundations of the "birth of a new life" is often limited to the "biology and pestle" course studied in the school years. Let's try to catch up and study the structure of one of the main characters of the process - the female egg.
At the birth of a girl in her ovary, the endocrine gland responsible for her hormonal background, there are about 7 million female gametes - eggs (gametes), each of which, theoretically, can become the basis of a new life after fertilization. But gradually with age, the number of eggs becomes smaller: in 20 years it is already 600 thousand, and after 60 they can not be found at all. Such a strong stock of female cells allows a woman to become a mother even if one or part of the other ovary is removed.
So, the egg cell (egg cell, ovum) is the largest living cell of the human body, the female reproductive cell is a rounded (slightly elongated or spherical) shape that ripens and is "stored" in the ovarian follicles. It is practically immobilized and before reaching the uterus it makes a path of about 10 cm in length along the internal villi of the oviduct within 4-7 days. The size of the egg is two times higher than the size of the sperm cell - the male germ cell and several dozen times - the size of other cells in the body. Its diameter is of the order of 100-170 μm. The female gamete is intended for transmission in the process of reproduction of a haploid set of 23 chromosomes (22 autosomal transmitting hereditary information + one sex X chromosome responsible for the sex of the unborn child).
What does the egg look like?
The scheme of the structure of a mature egg, which is formed after ovulation - the release of the egg from the follicle into the abdominal cavity, is presented below.
In general, the egg has a structure similar to other cells of the body: the nucleus, the cytoplasm, the restriction of the plasma membrane. Haploid nucleus with a set of the above chromosomes in the egg is in its center. The cytoplasm consists of a variety of ribosomes, elements of the endoplasmic reticulum and containing enzymes necessary for respiration of the mitochondrial cells. The outer sphere of the cytoplasm contains secretory (cortical) granules, which upon penetration into the egg of the sperm are released, acting on its shell, which as a result leads to a change in the structure of the oocyte and prevents the penetration of other spermatozoa. Active cortical grains will promote successful fertilization.
The shells of the egg also perform a protective function and the function of organizing its nutrition. Outside, the egg is surrounded by a shiny shell, covered with a layer of microvilli - this is the so-called follicular coat or radiant crown.
The polar body is a small cell that, together with the egg, is formed as a result of meiosis - the division of the progenitor cell during its maturation. It has been scientifically proven that the content of the polar body can be the basis for the diagnosis of genetic diseases.
Nutrition of the cell before its introduction into the uterine wall is carried out with the help of yolk granules-vesicles, filled with fats, a small amount of proteins, vitamins and microelements.
The quality of the maturing egg cell, its viability can be influenced by such factors of external influence as the cellular environment, biochemical composition and temperature of the environment of the egg. In addition, the mechanism of intracellular functioning has a significant effect in the process of its maturation. "Weak", not ripening egg often causes infertility. This can happen, for example, if the menstrual cycle lasts either less than 21 days, or more than 35 days. Under such conditions, the egg cell either does not "ripen", or becomes already incompetent. In the absence of ovulation, the ovaries do not produce follicles, in which ovules mature. Thus, without eggs, when spermatozoa enter, fertilization does not occur.