What occurs if a secondary oocyte is not fertilized?

When a secondary oocyte is not fertilized, it undergoes a process known as atresia. Atresia refers to the degeneration and resorption of the oocyte, which is a normal part of the ovarian cycle. If fertilization does not occur, the secondary oocyte is unable to complete meiosis II and instead disintegrates or is absorbed by the surrounding ovarian tissue. This process ensures that resources are not wasted on non-viable oocytes and allows the body to manage its reproductive capacity effectively.

In the absence of fertilization, the oocyte does not mature into a blastocyst, as that process is contingent on fertilization and subsequent cleavage. Additionally, without fertilization, there is no completion of meiosis II, since that process is triggered by sperm entry into the oocyte. Finally, the secondary oocyte will not implant into the endometrium; implantation is a step that occurs after the oocyte has been fertilized, leading to the development of an embryo that can then attach to the uterine lining. Overall, atresia is the definitive outcome for an unfertilized secondary oocyte.