行经是由于子宫内膜组织在月经周期的一定阶段中脱落而引起的。正常育龄妇女子宫内膜的周期性变化是一个缓慢的渐变过程,在一个月经周期中,子宫内膜的变化大致可分为两个时期。从行经终止到排卵发生,叫增生期。这一时期,在雌激素的影响下,腺体、血管和表面上皮基质增生。第二个时期叫黄体期,它从排卵发生到下一次月经来潮为止。黄体期中子宫内膜在雌激素与孕酮的作用下不断成熟,到下次行经前一周左右,雌、孕激素的分泌量开始下降,至行经发生时达最低点。由于雌、孕激素的这一“撤退”, Migration is due to endometrial tissue in a certain stage of menstrual cycle shedding caused. Periodic changes in the endometrium of normal women of childbearing age is a slow gradual process, in a menstrual cycle, changes in the endometrium can be divided into two periods. From termination to ovulation occurs, called the proliferative phase. During this period, glands, blood vessels and surface epithelial stroma proliferate under the influence of estrogen. The second period is called the luteal phase, which occurs from the ovulation until the next menstrual cramps. Luteal phase in the endometrium in the role of estrogen and progesterone continue to mature, to the next week before the menstrual cycle, the secretion of estrogen and progesterone began to decline, until the passing of the lowest point. Due to this “withdrawal” of estrogen and progestin,