Hormones control the two closely linked reproductive cycles in
human females—the uterine (or menstrual) cycle and the ovarian
cycle. During one uterine cycle, which is approximately 28 days
long, the lining of the uterus undergoes hormonally-regulated
changes, if no pregnancy has occurred. At the same time, the
hormones also cause a series of changes to take place in an ovary,
known as the ovarian cycle. The flowchart below describes the
events of the ovarian cycle.