The Physiology of the Menstrual Cycle: From Ovarian Follicles toEndometrial Shedding

Background: The menstrual cycle is a fundamental physiological rhythm in women that reflects the finely coordinated interplay between the hypothalamic–pituitary–ovarian (HPO) axis and the endometrium. It ensures reproductive capacity while serving as an indicator of systemic health. Disturbances in this cycle are often linked to conditions such as polycystic ovarian syndrome (PCOS), endometriosis, and luteal phase defects. Objective: This review aims to consolidate current knowledge on the physiology of the menstrual cycle, focusing on ovarian follicular dynamics, hormonal regulation, endometrial changes, and their clinical significance. Discussion: The cycle is broadly divided into ovarian (follicular, ovulatory, luteal) and uterine (proliferative, secretory, menstrual) phases, each governed by hormonal rhythms and feedback loops. The hypothalamus releases gonadotropin-releasing hormone (GnRH), stimulating pituitary secretion of FSH and LH, which regulate folliculogenesis and ovulation. Post-ovulation, corpus luteum–derived progesterone transforms the endometrium into a receptive state. In the absence of fertilization, luteolysis leads to withdrawal of hormonal support, causing endometrial ischemia and menstrual shedding. Disturbances in these processes can lead to infertility, irregular bleeding, and systemic endocrine disorders. Beyond reproduction, cyclical fluctuations in estrogen and progesterone influence immunity, cardiovascular function, metabolism, and neuropsychological health. Conclusion: Understanding menstrual physiology, from ovarian follicle development to endometrial shedding, is essential for advancing reproductive medicine and women’s health. It has implications for diagnosing menstrual disorders, developing contraceptives, improving assisted reproductive technologies, and addressing broader systemic effects of hormonal fluctuations.