äggbildningen

Eggbildningen, also known as oogenesis, is the process by which female gametes, or ova (eggs), are produced in the ovaries of sexually reproducing organisms. This complex biological process begins during fetal development and continues until menopause in humans.

In mammals, oogenesis starts with primordial germ cells that differentiate into oogonia. These oogonia undergo mitotic proliferation, increasing their numbers. Following this, oogonia develop into primary oocytes, which then enter meiosis I. Meiosis I is arrested in prophase I, and these primary oocytes remain in this state until puberty.

At puberty, hormonal signals trigger the completion of meiosis I for a selected group of primary oocytes each menstrual cycle. This division results in a large secondary oocyte and a small polar body. The secondary oocyte then begins meiosis II, which is arrested in metaphase II. Ovulation releases this secondary oocyte.

Fertilization by a sperm triggers the completion of meiosis II, producing a mature ovum and another polar body. If fertilization does not occur, the secondary oocyte degenerates. Throughout oogenesis, the cytoplasm of the oocyte is enriched with nutrients and essential molecules that will support the early development of an embryo. This process is tightly regulated by hormones, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which orchestrate the maturation and release of the egg.