Journal of Fertilization: In Vitro - IVF-Worldwide, Reproductive Medicine, Genetics & Stem Cell Biol
Open Access

Atretic Follicles: Their Role in Ovarian Function and Implications for Fertility

Weixin Qirong^{* *}Correspondence: Weixin Qirong, Department of Embryology, Peking University, Beijing, China, Email:

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Description

Folliculogenesis is the process by which ovarian follicles develop and mature in preparation for ovulation. However, not all follicles reach the stage where they can be released during ovulation. Some follicles undergo a natural process of degeneration and resorption. These follicles are called atretic follicles. In this article, we will explain what atretic follicles are, how they form, and their significance in ovarian function and fertility. Atretic follicles are ovarian follicles that have stopped developing and are undergoing degeneration. This process is a part of normal ovarian function. During each menstrual cycle, several follicles begin to mature under the influence of hormones, but typically only one will reach full maturity and be released during ovulation. The remaining follicles that do not reach this stage undergo atresia, or follicular degeneration, and eventually disappear.

Atretic follicles can be found at various stages of development, from primordial to mature follicles, but they all share the common characteristic of undergoing a process of cell death (apoptosis) and degeneration. Follicular atresia is a natural, regulated process by which ovarian follicles regress and are resorbed by the ovary. Atresia can occur at any stage of follicular development, but it is more common during the early stages of folliculogenesis. Primordial follicles are the earliest stage of follicle development, consisting of an oocyte surrounded by a single layer of granulosa cells. These follicles remain dormant until they are activated to begin maturation. However, many of these follicles will undergo atresia without ever reaching the later stages of development. As follicles progress from primordial to primary and secondary stages, some will begin to regress due to a lack of hormonal support or other regulatory factors. These follicles undergo atresia and are absorbed back into the ovarian tissue. Antral follicles are larger and have a fluid-filled cavity called an antrum. These follicles are typically more advanced in their development, and their degeneration can have significant consequences for fertility. Antral follicles may undergo atresia due to factors like hormonal imbalance, insufficient Follicle-Stimulating Hormone (FSH) levels, or abnormal growth signals. This stage of atresia is particularly important because it occurs just before ovulation. In some cases, a mature, pre-ovulatory follicle may undergo atresia instead of ovulating. This can occur when hormonal levels are disrupted or if the follicle fails to respond appropriately to the Luteinizing Hormone (LH) surge that triggers ovulation.

Follicular atresia is primarily driven by apoptosis, a form of programmed cell death. The exact mechanisms that trigger atresia are complex and involve several factors, including hormonal regulation, genetic signals, and cellular interactions. Follicular development is tightly controlled by hormones such as FSH and LH. If a follicle does not receive adequate hormonal signals or if it fails to respond properly to these hormones, it may undergo atresia. For example, low levels of FSH may prevent a follicle from progressing to the next stage of development, leading to its degeneration. Apoptosis plays a central role in the atresia process. It involves the activation of specific genes and proteins that trigger cell death in the granulosa cells, oocyte, and theca cells within the follicle. These cells are then phagocytized and cleared away by neighboring cells. The health and quality of the oocyte are also factors that influence follicular atresia. Follicles with oocytes that are genetically compromised or have defects may undergo atresia to prevent the release of a defective egg. This is a protective mechanism to ensure that only high-quality eggs are released for fertilization. The development of follicles requires a supply of nutrients and oxygen. Follicles that fail to develop appropriately may not receive sufficient resources, leading to their degeneration. This is particularly common in larger follicles that outgrow their blood supply, resulting in hypoxia and triggering atresia.

Conclusion

Atretic follicles are an integral part of ovarian function and the natural reproductive process. Their development and degeneration are normal, with atresia helping regulate the number of follicles and eggs available for ovulation. While atretic follicles typically do not contribute directly to fertility, their presence and dynamics can offer valuable insights into ovarian health and function. Understanding the role of atretic follicles can help in diagnosing and managing fertility issues, and may guide treatment decisions for women experiencing challenges with conception.