The physiological functions of the uterine endometrium (uterine lining) are preparation for implantation, maintenance of pregnancy if implantation occurs, and menstruation in the absence of pregnancy. The endometrium thus plays a pivotal role in reproduction and continuation of our species. Menstruation is a steroid-regulated event, and there are alternatives for a progesterone-primed endometrium, i.e., pregnancy or menstruation. Progesterone withdrawal is the trigger for menstruation. The menstruating endometrium is a physiological example of an injured or "wounded" surface that is required to rapidly repair each month. The physiological events of menstruation and endometrial repair provide an accessible in vivo human model of inflammation and tissue repair. Progress in our understanding of endometrial pathophysiology has been facilitated by modern cellular and molecular discovery tools, along with animal models of simulated menses. Abnormal uterine bleeding (AUB), including heavy menstrual bleeding (HMB), imposes a massive burden on society, affecting one in four women of reproductive age. Understanding structural and nonstructural causes underpinning AUB is essential to optimize and provide precision in patient management. This is facilitated by careful classification of causes of bleeding. We highlight the crucial need for understanding mechanisms underpinning menstruation and its aberrations. The endometrium is a prime target tissue for selective progesterone receptor modulators (SPRMs). This class of compounds has therapeutic potential for the clinical unmet need of HMB. SPRMs reduce menstrual bleeding by mechanisms still largely unknown. Human menstruation remains a taboo topic, and many questions concerning endometrial physiology that pertain to menstrual bleeding are yet to be answered.

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子宫内膜的生理学和月经的调节。

子宫内膜（子宫内膜）的生理功能是为着床做准备，如果发生着床则维持妊娠，以及在没有怀孕的情况下维持月经。因此，子宫内膜在我们物种的繁殖和延续中起着关键作用。月经是一种类固醇调节的事件，孕激素引发的子宫内膜有其他选择，即怀孕或月经。黄体酮戒断是月经的触发因素。月经期子宫内膜是受伤或“受伤”表面的生理例子，每个月都需要快速修复。月经和子宫内​​膜修复的生理事件提供了一种可接近的体内炎症和组织修复人体模型。现代细胞和分子发现工具以及模拟月经的动物模型促进了我们对子宫内膜病理生理学的理解。异常子宫出血 (AUB)，包括严重的月经出血 (HMB)，给社会带来了巨大的负担，影响了四分之一的育龄妇女。了解支撑 AUB 的结构性和非结构性原因对于优化和提供患者管理的精确性至关重要。仔细分类出血原因有助于做到这一点。我们强调了理解支持月经及其异常的机制的迫切需要。子宫内膜是选择性孕激素受体调节剂 (SPRM) 的主要目标组织。这类化合物对 HMB 的临床未满足需求具有治疗潜力。SPRM 减少月经出血的机制仍然很大程度上未知。人类月经仍然是一个禁忌话题，许多与月经出血有关的子宫内膜生理问题尚未得到解答。