GWEN SHOCKEY / SCIENCE PHOTO LIBRARY GWEN SHOCKEY / SCIENCE PHOTO LIBRARY
Illustration of the ovarian cycle (top), showing the developing follicle and ovum, the ovum's release (ovulation), and the follicle's transformation into corpus luteum. At bottom is the uterine cycle, where the lining of the uterus gradually thickens as the body prepares for a fertilized egg.
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