The Hypothalamic-Pituitary-Ovarian Axis and Regulation of the Menstrual Cycle

This chapter presents a focused, comprehensive, and rational framework for cataloging, considering, and assessing normal female reproductive function, developmental changes, abnormalities, and downstream effects of normal and abnormal menstrual function. It also furnishes a trellis upon which diagnostic methods and treatments may develop and be applied. While the menstrual cycle has many “moving parts,” it is the rational outcome of a straightforward, hierarchical series of feedback loops. This chapter mainly exposes the neuroendocrine limbs of gonadotropins feedback control but cannot do so without tying them to the target organs, the ovaries. Understanding these feedback loops allows expectation of the function of the female reproductive system and forecasts the effects of breaks in the loops. Downstream targets of the ovarian steroids such as the uterus, breasts, bones, metabolic tissues, central nervous system, and immune system are most affected by breaks in the menstrual cycle. However, none of the systems in the body are indifferent to the sex steroids. Some of the most obvious effects of breaks in the neuroendocrine feedback will be cited as examples of normal/abnormal function. Although comprehensive, this introductory chapter has constraints of detail and scope; these will be addressed by the chapters that follow.