性器官-女性性器官
The Sex Organs - The Female Sex Organs

月经周期：月经周期的功能

月经周期的基本功能容易总结：

子宫为可能的受精卵植入准备好内膜层。 如果植入没有发生，子宫内膜破溃并排到阴道。这种破溃和排放称为经血或简称为月经。

当经血已经停止时，子宫内膜开始增生并借此又启动另一个月经周期。在理论上，描述月经周期能够从它的任何一个时相开始。例如，为了医学计算的需要，月经周期被设定为从月经的第一天开始，终止于另一个周期之前的最末一天。但是，从月经周期生理变化的相互关系来看，以卵子生长和子宫内膜逐渐增厚来开始计算它的周期似乎最为适当。

The Menstrual Cycle: The function of the menstrual cycle

The basic function of the menstrual cycle is easily summarized:

It prepares the lining of the uterus for the possible implantation of a fertilized egg. If no implantation occurs, the lining breaks down and is discharged through the vagina. This discharge is known as menstrual bleeding or simply menstruation.

When the bleeding has stopped, the preparation of the uterine lining and thus the entire cycle starts again. Theoretically, a description of the menstrual cycle could begin with any of its phases. For the purposes of medical calculation, for example, the menstrual cycle is assumed to start with the first day of menstruation and to end with the last day before the next menstruation. However, in the present context it seems most useful to begin with the growth of the egg (ovum) and the gradual thickening of the uterine lining (endometrium).