O oocyte (also called the oocyte), at the time of ovulation, is associated with important layers that are unknown to most people. One of these layers is called radiated corona, which plays a fundamental role in human fertilization.
→ Oocyte and corona radiate formation
To understand what corona radiata is, it is essential to understand how oocytes form until their release in the ovulation process. These reproductive cells are formed in the ovaries and their development (oogenesis or ovulogenesis) starts still in the fetal stage.
Initially, primordial germ cells migrate to the gonads in the female. These primordial cells begin to divide, forming the oogonia. These cells begin, approximately in the third month of uterine development, to undergo divisions and enter the meiosis I prophysis. This step is interrupted in the diplotene phase, and the oogonia are called primary oocytes.
The primary oocytes are surrounded by a layer of cells, called follicular cells, that originate in the ovarian epithelium. The set formed by the oocyte and follicular cells is called ovarian follicles.
Initially, these follicles, even during fetal life, have only a layer of flattened follicular cells. At puberty, follicular growth begins. and modifications occur throughout the set, with the increase of oocytes and the multiplication of follicular cells.
The follicular cells divide and form a cuboidal-shaped layer of cells. At this point, the follicle is called unilaminar primer. The division continues and the follicular cells form a stratified epithelium called the granular layer. At this stage, the follicle is called multilaminar or preantral. The oocyte, then, with the granulosa cells, begins to secrete a layer of glycoproteins, forming the so-called zona pellucida.
With the development of the follicles, the accumulation of follicular fluid between the follicular cells begins. Because of this accumulation, the granulosa cells reorganize and form a cavity called the follicular antrum. At this stage, the follicles are called antral.
In the formation of the antrum, the granulosa cells organize themselves in the follicle wall, forming a thickening that supports the oocyte. A small group of these cells surround the oocyte and give rise tocorona radiata.
In each ovarian cycle, normally, the follicle reaches maturity and is released in the ovulation process. When the increase in luteinizing hormone occurs, meiosis I is completed and the secondary oocyte is formed, as well as the first polar body. Meiosis II is then initiated in the secondary oocyte. However, it is interrupted at the metaphysis and is only completed if there is fertilization.
→ Functions of the radiate corona
The corona radiata surrounds the oocyte and is released with this cell at the time of ovulation. This important layer produces chemical signals that attract sperm, that is, it contributes to a process known as chemotaxis.
In the process of fertilization, the corona radiata will be the first layer that the sperm will have to go through to get in contact with the oocyte. After penetrating this layer, the sperm will have to penetrate the zona pellucida and eventually fuse with the membrane of the female reproductive cell.
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/biologia/o-que-e-corona-radiata.htm