Oozyten

Oozyten, or oocytes, are the female gametes of animals and the cells that develop in the ovaries through the process of oogenesis. In most mammals, the development of oocytes begins before birth. Primordial germ cells migrate to the developing gonads and differentiate into oogonia, which proliferate and enter meiosis to become primary oocytes. These primary oocytes arrest in prophase I and form a finite pool that is established during fetal life. At puberty, hormonal cycles recruit a cohort of primary oocytes each menstrual cycle. Typically one primary oocyte progresses to complete meiosis I, producing a second oocyte and a first polar body. The second oocyte is released at ovulation and begins meiosis II, remaining arrested at metaphase II until fertilization. If sperm fertilizes the oocyte, meiosis II completes, yielding a mature ovum and a second polar body. If fertilization does not occur, the secondary oocyte degenerates.

Oocytes are large, cytoplasm-rich cells surrounded by supporting cells within the ovarian follicle and, after ovulation, by the zona pellucida. Their quality and quantity can influence fertility and developmental potential. In many species, maternal age is associated with increased chromosomal abnormalities and reduced embryo viability, partly due to accumulated cellular and mitochondrial changes in oocytes.

The term “Oozyten” is the German plural form of the English term “oocytes.” In English-language biology, the singular is oocyte and the plural is oocytes. The concept of oocytes is central to reproduction, development, and assisted reproductive technologies.