Ovum and ovogenesis

Egg cells, unlike the male reproductive cells, multiply, their number increases in embryos, females, ie, in females. When the fetus is still in the womb. Thus, the so-called primordial follicles are formed, located in the deep layers of the cortical substance of the ovary. Each such primordial follicle contains a young female sex cell - an ovony, surrounded by a single layer of follicular cells. Ovonium is repeatedly divided into mitotically, turning into primary oocytes (first-order oocytes), which are stored in the ovary of the girl until her puberty. At the beginning of puberty in the ovaries, about 300,000 primary oocytes with a diameter of about 30 μm each. Together with the surrounding two layers of cells of the follicular epithelium, the primary oocyte is the primary follicle.

In girls during puberty and in sexually mature women, the majority of primary oocytes perish. During the life of a woman, only 400-500 ova mature. Every 21-28 days, according to the individual menstrual cycle, usually one follicle (or, more rarely, two) reaches maturity. The diameter of the mature (bladder) follicle reaches 1 cm. Other follicles growing at this time undergo reverse development - atresia. On the site of death of such unripe and dead follicles there are structures that have been called atretic bodies.

In the process of maturation, the primary oocyte passes through the stages of meiosis. As a result of meiotic division, a secondary oocyte is formed that already has a single (haploid) set of chromosomes (n = 23), and a small, so-called polar body with the same (n = 23) set of chromosomes. In this case, the primary follicles are transformed into secondary follicles. Inside such follicles, fluid accumulates, and around each secondary oocyte, two membranes are formed: the cytolemma and the follicular cell layer. Thus, the secondary follicle turns into a blistered (ripened) follicle filled with a follicular fluid.

During the growth and development of primary follicles, the egg increases in size. Around it formed a transparent shell of glycosaminoglycans and other substances, and around this shell is a layer of cubic follicular cells secreting the follicular fluid containing female sex hormones - estrogens. At this time, the egg is surrounded by follicular cells and, together with the latter, it moves to the wall of the follicle, where it forms the egg-mound (cumulus oophorus). Thus, the primary follicle becomes a secondary (blister) follicle. Ovocite no longer increases in size, the follicles themselves continue to coalesce. In this phase of the oocyte with its surrounding transparent membrane (zona pellucida) and a layer of follicular cells, known as a radiant crown (corona radiata), is displaced to the top of the growing follicle. As the size of the follicle increases, the connective tissue around it becomes denser and forms an outer membrane - the flow follicula. In this shell numerous blood capillaries grow.

In teki distinguish two layers: the inner and outer. Near the inner layer of the skin near the blood capillaries are numerous interstitial cells, and the outer layer (membrane) of the current consists of a dense fibrous connective tissue. Within the mature follicle, reaching a diameter of 1 cm, there is a cavity containing a follicular fluid (liquor follicularis).

As the maturation of the follicle gradually reaches the surface layer of the ovary. During the period of ovulation, the wall of such a follicle bursts, the egg along with the follicular fluid enters the peritoneal cavity, where it falls on the fringe of the tube, and then into the abdominal (peritoneal) opening of the uterine tube. On the site of the bursted follicle remains a blood-filled depression in which a yellow body (corpus luteum) forms. If the fertilization of the egg does not occur, then the yellow body has small dimensions (up to 1.0-1.5 cm), there is not long and is called a cyclic (menstrual) yellow body (corpus uteum ciclicum, s.menstruationis). Later it sprouts with a connective tissue and gets the name of a whitish body (corpus albicans), which after a while resolves. If the egg is fertilized, then pregnancy occurs, the yellow body of pregnancy (corpus uteum graviditatis) increases in size, reaches 1.5-2.0 cm in diameter and exists throughout pregnancy, performing an intrasecretory function. In the future, it is also replaced by a connective tissue and turns into a whitish body (corpus albicans). In the places of the bursted follicles, depressions and folds remain on the surface of the ovary; their number increases with age.

[1], [2], [3]