The uterine cycle is the cycle of growth and sloughing of uterine lining. It causes development of the endometrium in perfect timing with the ovarian cycle. The uterine cycle has three phases: the menstrual phase, proliferative phase, and secretory phase.
The menstural phase begins with sloughing of the endometrium and menstrual flow (menstruation). Low estrogen and progesterone levels cause menstruation. Menstrual flow continues for days 1-5. In the proliferative phase, a pre-ovulatory surge of estrogen stimulates thickening of the endometrium (days 6-13).
Follicular estrogens exert positive feedback on the follicles to give estrogen surge, leading to ovulation on day 14. In the secretory phase, progesterone stimulates development of the endometrium and secretory glands (days 15-28). Without implantation, falling levels of progesterone trigger menstruation. In menopause (climacteric), the ovarian and uterine cycles cease (about age 45-55).
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