Basic review: endocrinology of the normal menstrual cycle

Area of Science:

• Reproductive endocrinology
• Gynecology
• Neuroendocrinology

Background:

• The normal menstrual cycle is orchestrated by intricate hormonal feedback loops involving the hypothalamus, pituitary gland, and ovaries.
• Hormonal regulation includes both long-loop feedback (e.g., estradiol to hypothalamus) and local ovarian control.
• Hormone concentration and timing are critical for their effects throughout the cycle.

Purpose of the Study:

• To elucidate the hormonal mechanisms governing the normal human menstrual cycle.
• To detail the roles of gonadotropins, estradiol, and progesterone in follicular development, ovulation, and luteal phase function.

Main Methods:

• Review of established physiological principles of the hypothalamic-pituitary-ovarian axis.
• Analysis of hormonal feedback mechanisms and their impact on gonadotropin secretion.
• Description of the biochemical events characterizing the follicular, ovulatory, and luteal phases.

Main Results:

• A single gonadotropin-releasing hormone (GnRH) controls both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release.
• Estradiol (E2) production during the follicular phase stimulates LH receptors and increases the gonadotropin pool, while inhibiting GnRH.
• Ovulation is triggered by an LH surge induced by positive E2 feedback, and corpus luteum development is primarily progesterone-driven and autonomous.

Conclusions:

• The menstrual cycle is a precisely regulated process involving dynamic hormonal interplay.
• Estradiol and progesterone play distinct, crucial roles in follicular development, ovulation, and luteal function.
• Understanding these hormonal dynamics is key to reproductive health and potential interventions.