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Steroidhormone secreted by the female reproductive system that functions mainly to regulate the condition of the endometrium (seeuterus), preparing it to accept a fertilized egg. If the egg is not fertilized, the level of progesterone drops, the uterine lining breaks down, and menstruation ensues. If the egg is fertilized (seepregnancy), the placenta produces progesterone, whose effects include preparing the mammary glands for lactation. Many forms of oral contraception use a synthetic progesterone.
This entry comes from Encyclopædia Britannica Concise. For the full entry on progesterone, visit Britannica.com.