What is Oogenesis?
Oogenesis is the process of the formation of female gametes. This process begins inside the fetus before birth. The steps in oogenesis up to the production of primary oocytes occur before birth. Primary oocytes do not divide further. They either become secondary oocytes or degenerate. It starts with a germ cell called oogonium and undergoes mitosis to increase in number.
Process of Oogenesis
The process containing in the following three stages:
- Pre-natal Stage: The primary oocyte grows while being arrested in meiosis-I. The follicular cells proliferate and form a stratified cuboidal epithelium. Such cells are known as granulosa cells. These cells secrete glycoproteins to form zona pellucida around the primary oocyte.
- Antral Stage: The fluid-filled area, present between granulosa cells, combines to form a central fluid-filled space called the antrum. These are known as secondary follicles. In every month cycle, these secondary follicles develop under the influence of follicle-stimulating hormone and luteinizing hormone.
- Pre-Ovulatory Stage: This stage is induced by LH surge, and meiosis-I completes here. Two haploid cells of unequal sizes are formed within the follicle. One of the daughter cells that receive less cytoplasm forms a polar body. This cell does not participate in ovum formation. The other daughter cell is known as the secondary oocyte. The two daughter cells undergo meiosis-II. The polar body replicates to form two polar bodies, while the secondary oocyte arrests in the metaphase stage of meiosis-II.
Spermatogenesis and oogenesis are two different forms of gametogenesis. Gametogenesis in the male is known as spermatogenesis and in the female is known as oogenesis, which results in the formation of ova in the female. Oogenesis completely differs from spermatogenesis in several ways.
Difference Between Spermatogenesis and Oogenesis
|The production of sperms from spermatogonia is known as spermatogenesis||The production of eggs from oogonia is known as oogenesis|
|Occurs in testes||It occurs inside the ovary|
|All stages are completed in testes||The major part of ovogenesis occurs inside the ovary. The last few stages occur in the oviduct.|
|It is a continuous process||It is a discontinuous process. The early stages take place in the fetus and the rest in later stages of life.|
|Produces motile gametes||Produces non-motile gametes|
|The Equal cytokinesis occurs during the spermatogenesis producing four sperms||Unequal cytokinesis occurs during oogenesis ultimately producing one ovum and four polar bodies.|