Menstrual Cycle
The lining of the uterus (endometrium) goes through changes during what is known as the menstrual cycle. The most familiar event of the menstrual cycle for all women is menstruation – the shedding of the endometrium. The menstrual cycle and the ovarian cycle occur simultaneously.
The 1st day of menstrual bleeding is commonly recognized as the 1st day of a new cycle.
During menstruation, the endometrium sheds to its base cell layer. Following menstruation the endometrium begins to grow again, rapidly creating a dense surface. This is knows as proliferation. Estrogen stimulates the growth of the endometrium.
After ovulation the increasing level of progesterone stimulates changes in the endometrium. It becomes secretory. The cells of the endometrium begin to move apart from each other and develop sugar and fat glands, capillaries, and cellular fluids. These changes make the endometrium suitable for implantation of a fertilized ovum. If pregnancy does not occur, the progesterone level falls. Without hormonal support, the endometrium once again sheds off as menstrual flow.
If fertilization does occur, the corpus luteum will continue to produce progesterone and support the endometrium until the placenta is developed enough to produce its own progesterone. This occurs at about 12 weeks gestation.
If there is insufficient hormonal support for the development and maintenance of the endometrium the woman may experience, premenstrual spotting, difficulty achieving pregnancy or spontaneous abortions (miscarriages).
