The Life Cycle of the Ovary

The ovary is the primary female reproductive endocrine organ, providing gametes for human reproduction and secreting several hormones that support and maintain multiple system functions. The life cycle of the ovary begins with genesis and progresses through growth and maturity, prosperity, decline, and exhaustion, reflected in the reproductive capacity and hormone-level changes. Physiological changes are closely related to the quantity and quality of follicles in the ovary. Starting at the embryonic stage, primordial germ cells (PGCs) migrate to the genital ridge to form the primordial follicle pool, peaking at 6–7 million primordial follicles in the ovary. However, the number of primordial follicles decreases due to spontaneous activation and atresia, and only 1–4 million remain at birth. After birth, primordial follicles continue to be recruited, and some of these continue developing during the first 4 weeks of life. However, the ovaries have almost no physiological function at this stage. After the first 4 weeks, ovarian development continues, albeit slowly. Between 4 weeks of age and early puberty, most follicles (50–70%) degenerate and go through atresia at various stages, but the ovaries gradually mature. At puberty, with the aid of the hypothalamic and pituitary hormones, the ovaries begin to produce mature eggs and secrete hormones and cytokines that support the physiological functions of the mature ovaries and maintain fertility and normal organ functions in the female. However, ovarian function declines with the continuous decrease in the number and quality of follicles, thereby initiating the perimenopausal period, characterized by a rapid decline in the follicle pool. Eventually, the follicle pool is exhausted, followed by loss of function, resulting in menopausal syndrome and systemic multiple organ function damage, thus seriously endangering a woman's health.